U.S. patent number RE47,591 [Application Number 15/626,636] was granted by the patent office on 2019-09-03 for led lamp, led illumination device, and led module.
This patent grant is currently assigned to PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.. The grantee listed for this patent is PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD.. Invention is credited to Yoshio Manabe, Yoko Matsubayashi, Kazuhiro Matsuo, Toshio Mori, Atsushi Motoya, Masanori Shimizu, Hiroshi Yagi.
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United States Patent |
RE47,591 |
Matsubayashi , et
al. |
September 3, 2019 |
LED lamp, LED illumination device, and LED module
Abstract
An LED lamp provides a strong red color with a natural
appearance. The LED lamp is provided with an LED module and a
filter. The LED module includes a blue LED with a main emission
peak in the 440 nm to 460 nm wavelength band, a green/yellow
phosphor that is excited by light emitted by the blue LED, and a
red phosphor that is excited by light emitted by at least one of
the blue LED and the green/yellow phosphor. The filter reduces the
spectral radiation intensity of at least a portion of the 570 nm to
590 nm wavelength band among light emitted by the LED module.
Inventors: |
Matsubayashi; Yoko (Osaka,
JP), Yagi; Hiroshi (Osaka, JP), Shimizu;
Masanori (Kyoto, JP), Manabe; Yoshio (Osaka,
JP), Motoya; Atsushi (Shiga, JP), Matsuo;
Kazuhiro (Osaka, JP), Mori; Toshio (Kyoto,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO., LTD. |
Osaka |
N/A |
JP |
|
|
Assignee: |
PANASONIC INTELLECTUAL PROPERTY
MANAGEMENT CO., LTD. (Osaka, JP)
|
Family
ID: |
44541739 |
Appl.
No.: |
15/626,636 |
Filed: |
June 19, 2017 |
PCT
Filed: |
February 16, 2011 |
PCT No.: |
PCT/JP2011/000856 |
371(c)(1),(2),(4) Date: |
July 26, 2012 |
PCT
Pub. No.: |
WO2011/108203 |
PCT
Pub. Date: |
September 09, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
13575430 |
Feb 16, 2011 |
9062851 |
Jun 23, 2015 |
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Foreign Application Priority Data
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Mar 1, 2010 [JP] |
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2010-044516 |
Dec 22, 2010 [WO] |
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PCT/JP2010/007431 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C
3/00 (20130101); C09K 11/7774 (20130101); F21K
9/232 (20160801); H01L 33/502 (20130101); H01L
33/504 (20130101); C03C 3/00 (20130101); F21V
3/12 (20180201); F21V 3/12 (20180201); F21K
9/232 (20160801); C09K 11/7774 (20130101); F21Y
2103/10 (20160801); F21K 9/64 (20160801); F21Y
2115/10 (20160801); F21Y 2103/10 (20160801); F21K
9/27 (20160801); F21Y 2115/10 (20160801); F21K
9/64 (20160801); F21K 9/27 (20160801); H01L
33/504 (20130101) |
Current International
Class: |
C09K
11/77 (20060101); F21K 99/00 (20160101); F21V
3/04 (20180101); C03C 3/00 (20060101); H01L
33/50 (20100101); F21V 3/12 (20180101); F21K
9/232 (20160101); F21K 9/64 (20160101); F21K
9/27 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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100352069 |
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Nov 2007 |
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CN |
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201262382 |
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Jun 2009 |
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CN |
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201373280 |
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Dec 2009 |
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CN |
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201408780 |
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Feb 2010 |
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CN |
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1930393 |
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Jun 2008 |
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EP |
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2000-11954 |
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Jan 2000 |
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JP |
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2003-331795 |
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Nov 2003 |
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JP |
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2004-193581 |
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Jul 2004 |
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JP |
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2007-116133 |
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May 2007 |
|
JP |
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2010-40558 |
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Feb 2010 |
|
JP |
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2008/087404 |
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Jul 2008 |
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WO |
|
Other References
Search report from E.P.O. dated Jul. 17, 2014 issued in European
Application No. 11750317.7. cited by applicant .
E.P.O. Office Action dated Mar. 23, 2015 issued in European
Application No. 11750317.7. cited by applicant .
Chinese Office Action dated Mar. 5, 2014 issued in Chinese Patent
Application No. 201180011579.6, with English language translation.
cited by applicant .
International Search Report dated Apr. 5, 2011 issued in
International Patent Application No. PCT/JP2011/000856, with
English language translation. cited by applicant .
Machine translation of JP 2010-040558, Feb. 18, 2010. cited by
examiner .
Machine translation of JP 2007-116133, May 10, 2007. cited by
examiner .
Machine translation of JP 2003-331795, Nov. 21, 2003. cited by
examiner .
"Method of Specifying Colour Rendering Properties of Light
Sources", Japanese Industrial Standard (JIS) Z 8726, 1990. (and
English Translation). cited by applicant .
"Classification of Fluorescent Lamps by Chromaticity and Color
Rendering Property", Japanese Industrial Standard (JIS) Z 9112,
2004. (and English Translation). cited by applicant.
|
Primary Examiner: Menefee; James A
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
.[.1. An LED lamp comprising: an LED light source including a blue
LED with a main emission peak in a wavelength band of 440 nm to 460
nm, a green/yellow phosphor that is excited by light emitted by the
blue LED, and a red phosphor that is excited by light emitted by at
least one of the blue LED and the green/yellow phosphor; and a
filter that reduces spectral radiation intensity of at least a
portion of a wavelength range from 570 nm to 590 nm among light
emitted by the LED light source, wherein a color of light
transmitted through the filter is light bulb color as specified by
Japanese Industrial Standard Z9112, and wherein a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 580 nm to 630 nm, and a full width at half maximum for
the maximum peak wavelength is in a range of 120 nm to 175
nm..].
.[.2. An LED lamp comprising: an LED light source including a blue
LED with a main emission peak in a wavelength band of 440 nm to 460
nm, a green/yellow phosphor that is excited by light emitted by the
blue LED, and a red phosphor that is excited by light emitted by at
least one of the blue LED and the green/yellow phosphor; and a
filter that reduces spectral radiation intensity of at least a
portion of a wavelength range from 570 nm to 590 nm among light
emitted by the LED light source, wherein a color of light
transmitted through the filter is warm white as specified by
Japanese Industrial Standard Z9112, and wherein a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 580 nm to 620 nm, and a full width at half maximum for
the maximum peak wavelength is in a range of 120 nm to 175
nm..].
.[.3. An LED lamp comprising: an LED light source including a blue
LED with a main emission peak in a wavelength band of 440 nm to 460
nm, a green/yellow phosphor that is excited by light emitted by the
blue LED, and a red phosphor that is excited by light emitted by at
least one of the blue LED and the green/yellow phosphor; and a
filter that reduces spectral radiation intensity of at least a
portion of a wavelength range from 570 nm to 590 nm among light
emitted by the LED light source, wherein a color of light
transmitted through the filter is white as specified by Japanese
Industrial Standard Z9112, and wherein a maximum peak wavelength of
mixed light before transmission through the filter, the mixed light
being a mix of light emitted by the green/yellow phosphor and light
emitted by the red phosphor, is in a wavelength range from 575 nm
to 610 nm, and a full width at half maximum for the maximum peak
wavelength is in a range of 120 nm to 180 nm..].
.[.4. An LED lamp comprising: an LED light source including a blue
LED with a main emission peak in a wavelength band of 440 nm to 460
nm, a green/yellow phosphor that is excited by light emitted by the
blue LED, and a red phosphor that is excited by light emitted by at
least one of the blue LED and the green/yellow phosphor; and a
filter that reduces spectral radiation intensity of at least a
portion of a wavelength range from 570 nm to 590 nm among light
emitted by the LED light source, wherein a color of light
transmitted through the filter is natural light as specified by
Japanese Industrial Standard Z9112, and wherein a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 525 nm to 610 nm, and a full width at half maximum for
the maximum peak wavelength is in a range of 125 nm to 180
nm..].
5. An LED lamp comprising: an LED light source including a blue LED
with a main emission peak in a wavelength band of 440 nm to 460 nm,
a green/yellow phosphor that is excited by light emitted by the
blue LED, and a red phosphor that is excited by light emitted by at
least one of the blue LED and the green/yellow phosphor; and a
filter that reduces spectral radiation intensity of at least a
portion of a wavelength range from 570 nm to 590 nm among light
emitted by the LED light source, wherein a color of light
transmitted through the filter is daylight as specified by Japanese
Industrial Standard Z9112, and wherein when a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 520 nm to 530 nm, a full width at half maximum for the
maximum peak wavelength is in a range of 135 nm to 170 nm, and when
the maximum peak wavelength of light before transmission through
the filter is in a wavelength range from 530 nm to 580 nm, the full
width at half maximum for the maximum peak wavelength is in a range
of 130 nm to 145 nm.
.[.6. The LED lamp according to claim 1, wherein the filter
includes a neodymium compound..].
.[.7. The LED lamp of claim 6, wherein the filter also serves as a
globe covering the LED light source..].
.[.8. The LED lamp of claim 6, further comprising: a globe covering
the LED light source, wherein the filter covers one of an inner
surface and an outer surface of the globe..].
.[.9. The LED lamp of claim 6, wherein the filter is shaped as a
plate and is provided with a space between the LED light source and
the filter..].
.[.10. The LED lamp of claim 6, wherein the filter is shaped as a
plate, and a translucent material is included between the LED light
source and the filter, and a refractive index of the translucent
material is lower than a refractive index of the filter and is
equal to or higher than a refractive index of a phosphor layer
including the green/yellow phosphor and the red phosphor in the LED
light source..].
.[.11. The LED lamp according to claim 6, wherein the filter is
made from a glass material..].
.[.12. The LED lamp according to claim 6, wherein the filter is
made from a resin material..].
.[.13. The LED lamp of claim 11, wherein the filter that includes
the neodymium compound has been manufactured by adding neodymium
oxide to soda glass that includes silica, an alkali metal oxide,
and an alkaline earth oxide..].
.[.14. The LED lamp of claim 11, wherein the filter that includes
the neodymium compound has been manufactured by adding neodymium
oxide powder to a silicon alkoxide that includes tetraethyl
orthosilicate..].
.[.15. The LED lamp of claim 6, further including: translucent
material having dispersed therein at least one of the green/yellow
phosphor and the red phosphor, wherein the filter is implemented by
dispersing a neodymium compound in the translucent material..].
.[.16. The LED lamp of claim 15, wherein a sol-gel method has been
used to manufacture the translucent material, so that the
translucent material has mixed therein the green/yellow phosphor,
the red phosphor, and the neodymium compound..].
.[.17. The LED lamp of claim 1, wherein a main emission peak of the
green/yellow phosphor is in a wavelength band of 500 nm to 595 nm,
and a main emission peak of the red phosphor is in a wavelength
band of 600 nm to 690 nm..].
.[.18. The LED lamp of claim 17, wherein a main emission peak of
the red phosphor is at least 626 nm..].
.[.19. An LED illumination device provided with the LED lamp of
claim 1..].
.[.20. An LED module comprising: a blue LED having a main emission
peak in a wavelength band of 440 nm to 460 nm; a green/yellow
phosphor that is excited by light emitted by the blue LED; a red
phosphor that is excited by light emitted by at least one of the
blue LED and the green/yellow phosphor; and a filter that reduces
spectral radiation intensity of at least a portion of a wavelength
range from 570 nm to 590 nm among light emitted by the blue LED,
the green/yellow phosphor, and the red phosphor, wherein a color of
light transmitted through the filter is light bulb color as
specified by Japanese Industrial Standard Z9112, and a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 580 nm to 630 nm, and a full width at half maximum for
the maximum peak wavelength is in a range of 120 nm to 175
nm..].
.[.21. An LED module comprising: a blue LED having a main emission
peak in a wavelength band of 440 nm to 460 nm; a green/yellow
phosphor that is excited by light emitted by the blue LED; a red
phosphor that is excited by light emitted by at least one of the
blue LED and the green/yellow phosphor; and a filter that reduces
spectral radiation intensity of at least a portion of a wavelength
range from 570 nm to 590 nm among light emitted by the blue LED,
the green/yellow phosphor, and the red phosphor, wherein a color of
light transmitted through the filter is warm white as specified by
Japanese Industrial Standard Z9112, and a maximum peak wavelength
of mixed light before transmission through the filter, the mixed
light being a mix of light emitted by the green/yellow phosphor and
light emitted by the red phosphor, is in a wavelength range from
580 nm to 620 nm, and a full width at half maximum for the maximum
peak wavelength is in a range of 120 nm to 175 nm..].
.[.22. An LED module comprising: a blue LED having a main emission
peak in a wavelength band of 440 nm to 460 nm; a green/yellow
phosphor that is excited by light emitted by the blue LED; a red
phosphor that is excited by light emitted by at least one of the
blue LED and the green/yellow phosphor; and a filter that reduces
spectral radiation intensity of at least a portion of a wavelength
range from 570 nm to 590 nm among light emitted by the blue LED,
the green/yellow phosphor, and the red phosphor, wherein a color of
light transmitted through the filter is white as specified by
Japanese Industrial Standard Z9112, and a maximum peak wavelength
of mixed light before transmission through the filter, the mixed
light being a mix of light emitted by the green/yellow phosphor and
light emitted by the red phosphor, is in a wavelength range from
575 nm to 610 nm, and a full width at half maximum for the maximum
peak wavelength is in a range of 120 nm to 180 nm..].
.[.23. An LED module comprising: a blue LED having a main emission
peak in a wavelength band of 440 nm to 460 nm; a green/yellow
phosphor that is excited by light emitted by the blue LED; a red
phosphor that is excited by light emitted by at least one of the
blue LED and the green/yellow phosphor; and a filter that reduces
spectral radiation intensity of at least a portion of a wavelength
range from 570 nm to 590 nm among light emitted by the blue LED,
the green/yellow phosphor, and the red phosphor, wherein a color of
light transmitted through the filter is natural light as specified
by Japanese Industrial Standard Z9112, and a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 525 nm to 610 nm, and a full width at half maximum for
the maximum peak wavelength is in a range of 125 nm to 180
nm..].
24. An LED module comprising: a blue LED having a main emission
peak in a wavelength band of 440 nm to 460 nm; a green/yellow
phosphor that is excited by light emitted by the blue LED; a red
phosphor that is excited by light emitted by at least one of the
blue LED and the green/yellow phosphor; and a filter that reduces
spectral radiation intensity of at least a portion of a wavelength
range from 570 nm to 590 nm among light emitted by the blue LED,
the green/yellow phosphor, and the red phosphor, wherein a color of
light transmitted through the filter is daylight as specified by
Japanese Industrial Standard Z9112, and when a maximum peak
wavelength of mixed light before transmission through the filter,
the mixed light being a mix of light emitted by the green/yellow
phosphor and light emitted by the red phosphor, is in a wavelength
range from 520 nm to 530 nm, a full width at half maximum for the
maximum peak wavelength is in a range of 135 nm to 170 nm, and when
the maximum peak wavelength of light before transmission through
the filter is in a wavelength range from 530 nm to 580 nm, the full
width at half maximum for the maximum peak wavelength is in a range
of 130 nm to 145 nm.
.Iadd.25. An LED lamp comprising: an LED light source including a
blue LED with a main emission peak in a wavelength band of 440 nm
to 460 nm, a green/yellow phosphor that is excited by light emitted
by the blue LED, and a red phosphor that is excited by light
emitted by at least one of the blue LED and the green/yellow
phosphor; and a filter that reduces spectral radiation intensity of
at least a portion of a wavelength range from 570 nm to 590 nm
among light emitted by the LED light source, wherein when a maximum
peak wavelength of mixed light before transmission through the
filter, the mixed light being a mix of light emitted by the
green/yellow phosphor and light emitted by the red phosphor, is in
a wavelength range from 520 nm to 530 nm, a full width at half
maximum for the maximum peak wavelength is in a range of 135 nm to
170 nm, and when the maximum peak wavelength of light before
transmission through the filter is in a wavelength range from 530
nm to 580 nm, the full width at half maximum for the maximum peak
wavelength is in a range of 130 nm to 145 nm..Iaddend.
.Iadd.26. The LED lamp according to claim 25, wherein a color
transmitted through the filter has a color temperature between 5700
to 7100 degrees Kelvin..Iaddend.
.Iadd.27. The LED lamp according to claim 25, wherein a special
color rendering index R9 of the LED lamp is 64 or
greater..Iaddend.
.Iadd.28. The LED lamp according to claim 25, wherein the filter is
configured as a globe covering the LED light source..Iaddend.
Description
TECHNICAL FIELD
The present invention relates to an LED lamp, an LED illumination
device, and an LED module, and in particular to technology for
improving the color rendering thereof.
BACKGROUND ART
In recent years, LED lamps have been widely used as a highly
energy-efficient replacement for incandescent light bulbs. One type
of white LED light source is a combination of gallium nitride (GaN)
blue LEDs and YAG yellow phosphor. Such an LED light source
produces blue light from the blue LED, which excites the yellow
phosphor particles, in turn producing yellow light. The combination
of the blue light and the yellow light yields white light.
Typically, objects viewed under a light source should preferably
appear to have natural coloring. In other words, a high color
rendering index is preferable. Various conventional forms of
technology have been proposed for enhancing the color rendering
index of an LED light source. For example, Patent Literature 1
proposes including neodymium oxide particles in a filter element
attached to the LED light source as a means of improving the
general color rendering index Ra. Neodymium oxide is known as a
material for filters that selectively absorbs light in a wavelength
band around 580 nm (for example, see Patent Literature 2). Japanese
Industrial Standard (JIS) Z8726 defines methods for evaluating the
color rendering index under a light source by using color rendering
indices that quantitatively assess the fidelity of color
reproduction under a lamp in comparison to a reference light
source.
CITATION LIST
Patent Literature
Patent Literature 1: Japanese Patent Application Publication No.
2004-193581 Patent Literature 2: Japanese Patent Application
Publication No. 2000-11954
SUMMARY OF INVENTION
Technical Problem
The general color rendering index Ra assesses how natural
mid-saturation test colors (R1 through R8; hereinafter referred to
as "middle colors") appear. While it is of course important for a
typical illumination source to show middle colors naturally, it may
also be important for other colors to appear natural. For example,
in places such as restaurants or stores that sell merchandise, not
only mere brightness but also the appearance of illuminated objects
is of great importance. In such contexts, there is a demand
therefore for not only middle colors but also strong colors, in
particular strong red, to appear natural.
Conventionally, technology for increasing the Ra through use of a
light filter or for making illuminated objects appear natural has
been disclosed in the literature. However, a way of simultaneously
improving the color rendering of both middle colors and of strong
red in order to achieve a natural appearance has not been
available.
In recent years, the use of LED light sources in industry as an
energy-efficient light source has increased dramatically. While
typically available LED light sources suffice for merely
guaranteeing brightness, the color rendering and the appearance of
illuminated objects achieved by such LED light sources is, in some
cases, insufficient. If an LED light source that simultaneously
improves the color rendering of both middle colors and of strong
red can be achieved, it can be expected that this energy-efficient
light source will be used even more widely in stores, restaurants,
and other contexts where not only brightness but also the
appearance of illuminated objects is of great importance.
Therefore, it is an object of the present invention to provide an
LED lamp that endows not only middle colors but also strong red
with a natural appearance.
Solution to Problem
An LED lamp according to the present invention comprises: an LED
light source including a blue LED with a main emission peak in a
wavelength band of 440 nm to 460 nm, a green/yellow phosphor that
is excited by light emitted by the blue LED, and a red phosphor
that is excited by light emitted by at least one of the blue LED
and the green/yellow phosphor; and a filter that reduces spectral
radiation intensity of at least a portion of a wavelength band of
570 nm to 590 nm among light emitted by the LED light source.
Advantageous Effects of Invention
The LED lamp with the above structure adopts a filter that reduces
the spectral radiation intensity of a specific wavelength band and
includes a red phosphor in the LED light source, thereby endowing
not only middle colors but also strong red with a natural
appearance.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates the structure of an LED lamp according to an
embodiment of the present invention.
FIGS. 2A and 2B show the results of optical spectra measurements
performed on an LED lamp, with FIG. 2A showing the optical spectra
for a Comparative Example, and FIG. 2B showing the optical spectra
for a Working Example.
FIGS. 3A and 3B list indices for assessing optical characteristics
of the LED lamp, with FIG. 3A listing indices for the Comparative
Example, and FIG. 3B listing indices for the Working Example.
FIG. 4 is a graph plotting simulation results for the color
classification of light bulb color (L).
FIG. 5 shows the simulation results for the color classification of
light bulb color (L).
FIG. 6 shows the simulation results for the color classification of
light bulb color (L).
FIG. 7 is a graph plotting simulation results for the color
classification of warm white (WW).
FIG. 8 shows the simulation results for the color classification of
warm white (WW).
FIG. 9 shows the simulation results for the color classification of
warm white (WW).
FIG. 10 is a graph plotting simulation results for the color
classification of white (W).
FIG. 11 shows the simulation results for the color classification
of white (W).
FIG. 12 shows the simulation results for the color classification
of white (W).
FIG. 13 is a graph plotting simulation results for the color
classification of natural light (N).
FIG. 14 shows the simulation results for the color classification
of natural light (N).
FIG. 15 shows the simulation results for the color classification
of natural light (N).
FIG. 16 is a graph plotting simulation results for the color
classification of daylight (D).
FIG. 17 shows the simulation results for the color classification
of daylight (D).
FIG. 18 shows the simulation results for the color classification
of daylight (D).
FIG. 19 shows the results of optical spectra measurements performed
on an LED lamp.
FIG. 20 lists indices for assessing optical characteristics of the
LED lamp in FIG. 19.
FIGS. 21A to 21C show differences in optical characteristics due to
differences in LED module structure, with FIG. 21A showing the
boundary surface for each layer when an air layer is present, FIG.
21B showing the boundary surface for each layer when a silicone
layer is present, and FIG. 21C showing filter transmittance in the
case of the air layer and of the silicone layer.
FIGS. 22A and 22B show the results of transmission spectra
measurements for each form of inclusion of neodymium as well as the
results of optical spectra measurements performed on an LED
lamp.
FIG. 23 lists indices for assessing optical characteristics of the
LED lamp for each form of inclusion of neodymium.
FIGS. 24A through 24D show modifications to the structure of the
LED module.
FIGS. 25A and 25B show modifications to the placement of the
filter.
FIG. 26 shows a modification to the structure of the LED lamp.
FIG. 27 shows the structure of an LED illumination device.
FIG. 28 shows the structure of an endoscope system.
FIGS. 29A and 29B are xy chromaticity diagrams indicating a
chromaticity range of colors reproducible by a display unit and
chromaticity ranges of various body tissues, with FIG. 29A showing
the entirety of the ranges, and FIG. 29B showing a magnified view
of portion A.
DESCRIPTION OF EMBODIMENTS
The following describes an embodiment of the present invention in
detail with reference to the drawings.
Structure
FIG. 1 illustrates the structure of an LED lamp according to an
embodiment of the present invention, with a portion of the LED lamp
cut away.
An LED lamp 1 is a bulb-shaped lamp that replaces an incandescent
light bulb. An E screw base 3 is attached to the proximal end of a
body 2. To the distal end 4, an LED module 5 that emits white light
and a globe 6 covering the LED module 5 are attached.
Within the LED module 5, blue LEDs 12 are mounted on a circuit
board 11. The blue LEDs 12 are sealed by a translucent material 13
formed from silicone resin or the like. A green/yellow phosphor 14
and a red phosphor 15 are dispersed in the translucent material 13.
The LED light source is formed by the combination of the blue LEDs
12, the green/yellow phosphor 14, and the red phosphor 15.
The blue LEDs 12 have a main emission peak in the 440 nm to 460 nm
wavelength band. The LEDs may be, for example, gallium nitride
LEDs. Note that the "main emission peak" refers to the emission
peak with the largest peak value in the emission spectrum.
The green/yellow phosphor 14 is excited by light emitted by the
blue LEDs 12, thereby emitting green/yellow light. Green phosphor
has a main peak in the 500 nm to 540 nm wavelength band, whereas
yellow phosphor has a main emission peak in the 545 nm to 595 nm
wavelength band. Phosphor particles generally exhibit great
variation. As a consequence, phosphor particles classified as
yellow in terms of composition may be classified as green in terms
of emission peak, and vice-versa. Considering how these two types
of phosphor particles cannot always be distinguished, the term
"green/yellow phosphor" is employed in the present description.
The red phosphor 15 is excited by either the light emitted by the
blue LEDs 12 or by the green/yellow phosphor 14, or is excited by
both, thereby emitting red light. The red phosphor 15 has a main
emission peak in the 600 nm to 690 nm wavelength band.
A filter 16 that reduces the spectral radiation intensity of at
least a portion of the 570 nm to 590 nm wavelength band of light
emitted by the LED light source is disposed on the circuit board
11. This filter may, for example, be made from glass or resin
including a neodymium compound (a representative example being
neodymium oxide).
Generally, the full width at half maximum of an LED emission peak
is narrow, whereas the full width at half maximum of a phosphor
emission peak is wide. As a result, longer wavelengths of the
emission peak of the green/yellow phosphor overlap with shorter
wavelengths of the emission peak of the red phosphor. As a result,
the spectral radiation intensity at this overlapping wavelength
band is intensified, leading to an unnatural appearance for
illuminated objects, which appear excessively yellow. To address
this problem, a filter that reduces the spectral radiation
intensity in the overlapping wavelength band is provided in the
present embodiment, thereby preventing the spectral radiation
intensity in the overlapping wavelength band from becoming too
strong. This provides illuminated objects with a natural-looking
color.
Note that in order to avoid overlap of the emission peaks, it would
appear plausible to use a combination of blue LEDs, green LEDs, and
red LEDs in the LED light source, instead of using a red phosphor.
Using LEDs for all three primary colors, however, is simply not
realistic with present technology. For example, since the luminous
efficiency of currently available green LEDs is low, it would be
necessary to use a large number of green LEDs in the LED light
source in order to maintain the green spectral radiation intensity
at a certain level. Furthermore, the spectral radiation intensity
of currently available red LEDs varies according to temperature. It
would thus be necessary to provide a temperature sensor and perform
feedback control in order to maintain the red spectral radiation
intensity at a certain level. Given these problems, using LEDs for
all three primary colors would be disadvantageous in terms of both
size and cost. By contrast, the present embodiment is realistic
given the state of current technology and offers advantages in
terms of both size and cost.
The following are examples of green phosphors.
Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+; Tb.sub.3Al.sub.5O.sub.12:
Ce.sup.3+; BaY.sub.2SiAl.sub.4O.sub.12: Ce.sup.3+;
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12: Ce.sup.3+; (Ba,
Sr).sub.2SiO.sub.4: Eu.sup.2+; CaSc.sub.2O.sub.4: Ce.sup.3+;
Ba.sub.3Si.sub.6O.sub.12N.sub.2: Eu.sup.2+; .beta.-SiAlON:
Eu.sup.2+; SrGa.sub.2S.sub.4: Eu.sup.2+.
The following are examples of yellow phosphors.
(Y,Gd).sub.3Al.sub.5O.sub.12: Ce.sup.3+; Y.sub.3Al.sub.5O.sub.12:
Ce.sup.3+, Pr.sup.3+; (Tb, Gd).sub.3Al.sub.5O.sub.12: Ce.sup.3+;
(Sr, Ba).sub.2SiO.sub.4: Eu.sup.2+; (Sr, Ca).sub.2SiO.sub.4:
Eu.sup.2+; CaSi.sub.2O.sub.2N.sub.2: Eu.sup.2+; Ca-.alpha.-SiAlON:
Eu.sup.2+; Y.sub.2Si.sub.4N.sub.6C: Ce.sup.3+; CaGa.sub.2S.sub.4:
Eu.sup.2+.
The following are examples of red phosphors. Ca-.alpha.-SiAlON:
Eu.sup.2+; CaAlSiN.sub.3: Eu.sup.2+; (Sr, Ca)AlSiN.sub.3:
Eu.sup.2+; Sr.sub.2Si.sub.5N.sub.8: Eu.sup.2+; Sr.sub.2(Si,
Al).sub.5(N, O).sub.8: Eu.sup.2+; CaS: Eu.sup.2+; La.sub.2O.sub.2S:
Eu.sup.3+.
Comparison Between Working Example and Comparative Example
The following describes a specific Working Example of the present
invention in comparison with a Comparative Example.
FIGS. 2A and 2B show the results of optical spectra measurements
performed on an LED lamp, with FIG. 2A showing the optical spectra
for the Comparative Example, and FIG. 2B showing the optical
spectra for the Working Example.
As the Comparative Example, an LED light source was prepared with a
combination of blue LEDs and YAG phosphor, and as the Working
Example, an LED light source was prepared with a combination of
blue LEDs, YAG phosphor, and red phosphor. As the filter, a thin
plate of soda glass including approximately 8% neodymium oxide was
prepared. The optical spectrum was measured while changing the
thickness of the filter between 0 mm, 0.27 mm, 0.43 mm, 0.5 mm, 0.6
mm, 0.7 mm, and 1 mm. Note that a thickness of 0 mm for the filter
means that no filter was provided. The optical spectrum for 0 mm
thus corresponds to the optical spectrum of the LED light
source.
As shown in FIGS. 2A and 2B, upon transmission of light from the
LED light source through the filter, the spectral radiation
intensity in the 570 nm to 590 nm wavelength band decreased.
Furthermore, increasing the thickness of the filter amplified the
decrease in spectral radiation intensity.
A comparison of FIG. 2A with FIG. 2B shows that, as compared to the
Comparative Example, the emission peak of light before transmission
through the filter shifted towards longer wavelengths and the full
width at half maximum grew larger in the Working Example. This is
because red phosphor is included in the LED light source of the
Working Example yet not in the LED light source of the Comparative
Example.
FIGS. 3A and 3B list indices for assessing optical characteristics
of the LED lamp, with FIG. 3A listing indices for the Comparative
Example, and FIG. 3B listing indices for the Working Example. The
indices listed for the LED lamp are the correlated color
temperature Tc, the deviation duv, the general color rendering
index Ra, the color gamut surface ratio Ga, the conspicuity index
M, the special color rendering indices R9 and R15, the color gamut
surface ratio Ga4, and the flux ratio. First, the characteristics
of each index is described before assessing the optical
characteristics of the LED lamp based on the indices.
The color gamut surface ratio Ga is listed in the reference column
of JIS Z8726 as an alternative method for evaluating color
rendering, without using color rendering indices. Specifically, the
value of the color gamut surface ratio Ga is obtained as follows.
First, chromaticity coordinates are obtained for eight test colors,
numbered 1 through 8, under a reference light source and under a
test light source. The coordinates are plotted in the U*V* plane,
and the surface area of each resulting octagon is calculated. The
surface area of the octagon for the test light source is then
divided by the surface area of the octagon for the reference light
source, and the resulting surface area ratio is multiplied by
100.
A color gamut surface ratio Ga of under 100 is indicative of
decreased saturation, and thus of a tendency toward dull colors. In
contrast, a color gamut surface ratio Ga of over 100 is indicative
of increased saturation, and thus of a tendency toward vivid
colors. Typically, as the color saturation of an object increases,
the appearance of the object improves. The color gamut surface
ratio Ga is therefore a suitable index for assessing whether a
color is eye-pleasing.
The conspicuity index M is an index indicating the perceived
conspicuity of a color. The degree of conspicuity of a color
subject that is illuminated by the test light source is expressed
by the color gamut surface area of a four-color test subject. The
color system used is the brightness (B) and colorfulness (Mr-g and
My-b) of a non-linear color-appearance model proposed by Nayatani
et al. (for example, in Color Research and Application, 20(3),
1995). The conspicuity index M is calculated as follows, using the
color gamut surface area of the four-color test subject.
M=[G(S,1000 1x)/G(D65,1000 1x)].sup.1.6.times.100
where G(S, 1000 1x) represents the color gamut surface area of the
four-color test subject when illuminated by the test light source
at 1000 1x, and G (D65, 1000 1x) represents the color gamut surface
area of the four-color test subject illuminated by the reference
light source D65 at 1000 1x. As the conspicuity index M increases,
colors of subjects, such as the green of flowers or foliage, appear
more conspicuous.
The special color rendering index R9 is calculated based on test
color No. 9 (strong red) defined by JIS Z8726. Similarly, the
special color rendering index R15 is calculated based on test color
No. 15 (Japanese skin color) defined by JIS Z8726.
The color gamut surface ratio Ga4 is calculated using R9 through
R12, which are special color rendering indices calculated based on
high-saturation test colors 9 through 12. Specifically, the color
gamut surface ratio Ga4 is obtained by the same method as for
calculating Ga for test colors R1 through R8, using test colors R9
through R12 instead. R1 through R8 are selected from among
mid-saturation test colors in order to assess slight differences in
the color appearance of natural objects. On the other hand, R9
through R12 are selected from among high-saturation test colors in
order to assess the appearance of strongly colored objects.
Therefore, Ga4 allows for accurate assessment of whether an object
intended to appear vivid does in fact appear so.
The flux ratio is a ratio of the flux after addition of the filter
to the flux before addition of the filter. The flux ratio thus
indicates the decrease in spectral radiation intensity due to the
filter.
As shown in FIGS. 3A and 3B, the correlated color temperature of
the Comparative Example and the Working Example is near 3500 K,
which corresponds to the light color classification of "warm white"
as specified by JIS Z9112. The inclusion of "air" in the filter
thickness entries indicates that measurements were performed with a
gap between the LED light source and the filter.
In the Comparative Example, Ra, Ga, M, R9, R15, and Ga4 increased
as the thickness of the glass plate including neodymium oxide,
which served as the filter, increased. For example, R9, which
assesses the appearance of strong red, was -37 without a filter, 59
at a thickness of 0.7, and 91 at a thickness of 1 mm. On the other
hand, as the thickness of the filter increased, the flux ratio
decreased. This is because as the thickness of the filter
increases, the light transmitted through the filter decreased.
Currently, as no standards for the color rendering of a LED lamp
exist, the desirable range of R9 for an LED lamp has not been
established. Therefore, in the present description, the desirable
range of R9 for an LED lamp is assumed to be 64 or greater in view
of JIS Z9112, which specifies the color rendering of a broadband
fluorescent lamp. This is based on how the minimum value for high
color rendering (color rendering AA) R9 in JIS Z9112 is 64.
Strictly speaking, the minimum value of R9 is specified for each
light color classification. In this case, the smallest value among
the minimum values was selected.
Furthermore, the desirable range of the flux ratio in the present
description is "70% or greater". This is based on how the flux
ratio of a high color rendering fluorescent lamp (color rendering
AA) to an existing, typical fluorescent lamp is approximately
70%.
Based on these values, the present description applies the
condition "R9 of 64 or greater and flux ratio of 70%" as the
assessment standard for an LED lamp.
JIS Z9112 also specifies the minimum value of R9 for the most
superior type of high color rendering (color rendering AAA). In
this case as well, the minimum value is specified for each light
color classification, with the largest value being 88. Therefore,
if the value of R9 for the LED light source is 88 or greater, the
LED light source already achieves color rendering AAA and thus does
not require a separate filter. Accordingly, the present description
focuses on LED lamps using an LED light source with an R9 value of
less than 88.
As shown in FIG. 3A, the Comparative Example does not satisfy the
above assessment standard. When the flux ratio is 70% or greater,
the value of R9 is greatest when the thickness of the filter is 0.7
mm. Even so, however, the value of R9 does not reach a value of 64
or greater. This demonstrates that, for an LED light source
including blue LEDs and YAG phosphor, it is difficult to show a
strong red color naturally while maintaining a certain degree of
efficiency when the correlated color temperature is approximately
3500 K, i.e. for the light color classification of warm white, even
if a filter is attached to the LED light source.
In the Working Example, Ga, M, and Ga4 increased as the thickness
of the filter increased, whereas the flux ratio decreased. This is
the same tendency as in the Comparative Example. On the other hand,
the value of Ra was maintained at 80 or greater regardless of the
thickness of the filter. Furthermore, R9 and R15 increased as the
filter grew thicker, reaching maximum values at a filter thickness
of 0.43 mm and decreasing for greater thicknesses. One possible
reason explaining this behavior of R9 and R15 is as follows. As the
filter grows thicker, the chromaticity coordinates of the test
light source approach the chromaticity coordinates of the reference
light source in the U*V* plane, thus reducing color distortion.
When the filter grows even thicker, however, the chromaticity
coordinates of the test light source surpass and move away from the
chromaticity coordinates of the reference light source, thus
causing color distortion to increase. Since Ga4 simply increases,
this interpretation seems natural. Note that when R9 decreases
after reaching a maximum value, strong colors appear even stronger.
In such cases, then, a relatively favorable appearance is still
often achieved. Excessive strength, however, does appear unnatural
and tends to be considered problematic during actual use.
Therefore, taking color distorted to be too strong into
consideration as well, the desirable range is set as "R9 of 64 or
greater".
As shown in FIG. 3B, in the Working Example, many cases satisfied
the assessment standard of "R9 of 64 or greater and flux ratio of
70% or greater". Adding a filter to an LED light source that
includes blue LEDs, YAG phosphor, and red phosphor therefore
achieves a natural appearance for strong red while maintaining a
certain degree of efficiency.
On the other hand, with the same filter thickness, flux decreases
by approximately 5% in the Working Example, which included blue
LEDs, YAG phosphor, and red phosphor, as compared to the
Comparative Example, which included blue LEDs and YAG phosphor. In
other words, when taking the flux for "no filter" in the
Comparative Example as a standard, the values listed for the flux
ratio of the Working Example in FIG. 3B each decrease by
approximately 5%. Even taking this decrease into consideration,
however, the flux ratio in the Working Example is still 70% or
greater for a filter thickness of 0.6 mm. The Working Example thus
achieved a flux ratio of 70% or greater with respect to "no filter"
in the Comparative Example and also obtained a value of 64 or
greater for R9.
With this structure, both an LED lamp that prioritizes efficiency
and an LED lamp that prioritizes color rendering can be created to
have the same phosphor composition, being distinguished instead by
the presence or absence of a filter. Since the price of phosphor
varies depending on the amount ordered, the above structure leads
to a lower cost for phosphor, thus allowing for the manufacture of
inexpensive LED lamps.
Simulations
The inventors performed simulations in order to test which spectrum
would yield light chromaticity coordinates within the light color
classification specified by JIS Z9112 before transmission through
the filter and would satisfy the assessment standard of "R9 value
of 64 or greater and flux ratio of 70%" for light after
transmission through the filter. Note that the simulations were
performed for each color classification specified by JIS Z9112.
Furthermore, the simulations were performed with a lower limit of
-2 for the duv value of the color classification, since duv lowers
upon application of a filter.
Light Bulb Color
FIG. 4 is a graph plotting simulation results for the color
classification of light bulb color (L). FIGS. 5 and 6 show the
simulation results for the color classification of light bulb color
(L). In FIGS. 5 and 6, the "color classification point" represents
the limit chromaticity coordinates for each color specified by JIS
Z9112. A color classification point that could not be achieved is
left blank.
As shown in FIGS. 5 and 6, the green/yellow phosphors prepared for
the simulations were YAG phosphors having respective main peaks at
535 nm, 540 nm, 550 nm, 555 nm, and 560 nm, and silicate phosphors
(listed as "green") having a main emission peak at 525 nm. The red
phosphors (listed as "red") that were prepared had respective main
emission peaks at 645 nm and 620 nm. The blue LEDs were assumed to
have a main emission peak between 440 nm and 460 nm.
First, the intensities of the blue light, green/yellow light, and
red light were adjusted to achieve light bulb color light, and the
light spectrum at that point was calculated. The maximum peak
wavelength and the full width at half maximum were then calculated
as indices characterizing the light spectrum, and the indices Ra,
Ga, M, R9, R15, and Ga4 for the light spectrum were also
calculated.
FIG. 4 is a plot of the test light sources in FIGS. 5 and 6. The
value of R9 before transmission through the filter is indicated by
each point. As FIG. 4 shows, the value of R9 generally tended to
increase as the peak wavelength and the full width at half maximum
increased. Circles in FIG. 4 indicate a test light source in which
the green/yellow phosphor was YAG with a peak wavelength between
535 nm and 560 nm, and in which the peak wavelength of the red
phosphor was 645 nm. Squares indicate a test light source in which
the green/yellow phosphor was YAG with a peak wavelength between
535 nm and 560 nm, and in which the peak wavelength of the red
phosphor was 620 nm Triangles indicate a test light source in which
the green/yellow phosphor was silicate with a peak wavelength of
525 nm, and in which the peak wavelength of the red phosphor was
between 645 nm and 620 nm. Furthermore, shapes with white centers
indicate either data for which the R9 value did not reach 64 or
greater when the flux ratio was maintained at 70% or greater
despite addition of a filter, or data for which addition of a
filter was not necessary. Data for which addition of a filter was
not necessary refers to when the R9 value was high to begin with,
reaching 88 or greater (color rendering AAA), or to when the value
of R9 was less than 88, yet the reason for the decrease could be
assumed to be due to the chromaticity coordinates for the test
light sources having exceeded the chromaticity coordinates of the
reference light source. Filled-in shapes indicate data for which
the R9 value was 88 without a filter, yet which satisfied the
assessment standard of "R9 of 64 or greater and flux ratio of 70%
or greater" when a filter was added.
Based on these data, for the color classification of light bulb
color (L), it is possible to provide an LED lamp that achieves a
natural appearance for strong red while maintaining a certain
degree of efficiency by adding a filter when the maximum peak
wavelength in the light spectrum before transmission through the
filter is in a range of 580 nm to 630 nm and the full width at half
maximum for the maximum peak wavelength is in a range of 120 nm to
175 nm (i.e. within the dashed rectangle in FIG. 4). Note that the
"maximum peak wavelength" refers to the maximum among peak
wavelengths of light emitted by phosphors.
The same simulation as for the light bulb color was performed for
the colors warm white, white, natural light, and daylight as well,
and assessment was made with the same assessment standard. The
following lists the simulation results.
Warm White
FIG. 7 is a graph plotting simulation results for the color
classification of warm white (WW). FIGS. 8 and 9 show the
simulation results for the color classification of warm white
(WW).
For the color classification of warm white (WW), it is possible to
provide an LED lamp that achieves a natural appearance for strong
red while maintaining a certain degree of efficiency by providing a
filter when the maximum peak wavelength in the light spectrum
before transmission through the filter is in a range of 580 nm to
620 nm and the full width at half maximum for the maximum peak
wavelength is in a range of 120 nm to 175 nm (i.e. within the
dashed rectangle in FIG. 7).
White
FIG. 10 is a graph plotting simulation results for the color
classification of white (W). FIGS. 11 and 12 show the simulation
results for the color classification of white (W).
For the color classification of white (W), it is possible to
provide an LED lamp that achieves a natural appearance for strong
red while maintaining a certain degree of efficiency by providing a
filter when the maximum peak wavelength in the light spectrum
before transmission through the filter is in a range of 575 nm to
610 nm and the full width at half maximum for the maximum peak
wavelength is in a range of 120 nm to 180 nm (i.e. within the
dashed rectangle in FIG. 10).
Natural Light
FIG. 13 is a graph plotting simulation results for the color
classification of natural light (N). FIGS. 14 and 15 show the
simulation results for the color classification of natural light
(N).
For the color classification of natural light (N), it is possible
to provide an LED lamp that achieves a natural appearance for
strong red while maintaining a certain degree of efficiency by
providing a filter when the maximum peak wavelength in the light
spectrum before transmission through the filter is in a range of
525 nm to 610 nm and the full width at half maximum for the maximum
peak wavelength is in a range of 125 nm to 180 nm (i.e. within the
dashed rectangle in FIG. 13).
Daylight
FIG. 16 is a graph plotting simulation results for the color
classification of daylight (D). FIGS. 17 and 18 show the simulation
results for the color classification of daylight (D).
For the color classification of daylight (D), it is possible to
provide an LED lamp that achieves a natural appearance for strong
red while maintaining a certain degree of efficiency by providing a
filter when the maximum peak wavelength in the light spectrum
before transmission through the filter is in a range of 520 nm to
530 nm and the full width at half maximum for the maximum peak
wavelength is in a range of 135 nm to 170 nm, or when the peak
wavelength is in a range of 530 nm to 580 nm and the full width at
half maximum for the maximum peak wavelength is in a range of 130
nm to 145 nm (i.e. within the dashed rectangles in FIG. 16).
Differences in Filter Effect
Next, the differences in the effects of using a filter based on
differences in LED module structure are described.
FIG. 19 shows the results of optical spectra measurements performed
on an LED lamp. FIG. 20 lists indices for assessing optical
characteristics of the LED lamp in FIG. 19. As shown in FIG. 20,
the correlated color temperature is near 2800 K, which corresponds
to the light color classification of "light bulb color".
Here, the presence of a gap between the LED light source and the
filter (listed as "air") is compared with a silicone packing
between the LED light source and the filter (listed as "silicone").
As shown in FIG. 20, when the thickness of the filter is the same,
the flux ratio decreased in the case of the silicone layer as
compared to the air layer, whereas the indices Ra, R9, R15, Ga, and
M all increased. Inclusion of the silicone layer is thus
preferable.
The reason for this tendency can be explained as follows. FIGS. 21A
to 21C show differences in optical characteristics due to
differences in LED module structure. FIG. 21A shows the boundary
surface and critical angle for each layer when the air layer is
present. FIG. 21B shows the boundary surface and critical angle for
each layer when the silicone layer is present. FIG. 21C shows the
transmittance of the filter in the case of the air layer and the
case of the silicone layer.
The critical angle is defined by the refractive indices of the
media along the boundary surface and refers to the smallest angle
of incidence for which all light is reflected when light enters the
medium with the smaller refractive index from the medium with the
larger refractive index. The transmittance of the filter is
calculated based not on the parallel light used at the time of
material measurement, but rather based on actual measured values
before and after addition of the filter.
When the silicone layer is present, the value of .theta.m2
increases as compared to the case of the air layer, and the amount
of light fully reflected at the boundary surface (2) with the
phosphor layer decreases. Therefore, a larger amount of light first
enters the soda glass. After propagating within the glass, a
portion of the light traces the following path: the light returns
to the phosphor layer and is diffused, the angle of incidence
changes, and the light again traverses the filter to reach the
boundary surface (3). As a result, the number of propagations
within the glass increases, thus enhancing the filter effect. As
shown in FIG. 21C, the spectral radiation intensity of the filter
decreased in the case of the silicone layer as compared to the air
layer. Note that the same advantageous effect is achieved as long
as the refractive index of the translucent material between the
phosphor layer and the filter is similar to or higher than the
refractive index of the phosphor layer, and lower than the
refractive index of the filter.
Next, differences in the filter effect due to differences in the
form of inclusion of neodymium are described.
To illustrate these differences, glass that includes neodymium
oxide (hereinafter referred to as a "glass plate"), silicone resin
having dispersed therein powder of glass that includes neodymium
oxide (hereinafter referred to as "glass powder"), and silicone
resin having dispersed therein neodymium oxide powder (hereinafter
referred to as "Nd powder") were prepared.
FIGS. 22A and 22B show the results of transmission spectra
measurements for each form of inclusion of neodymium as well as the
results of optical spectra measurements performed on an LED lamp.
FIG. 23 lists indices for assessing optical characteristics of the
LED lamp for each form of inclusion of neodymium.
As shown in FIGS. 22A and 22B, the transmittance of the glass plate
is higher than the glass powder and the Nd powder in wavelength
bands other than the 570 nm to 590 nm wavelength band. In
comparison with the glass powder and the Nd powder, it is therefore
possible to suppress the reduction in flux ratio of the glass plate
(see FIG. 23). On the other hand, it is easier to process glass
powder and Nd powder as compared to a glass plate. Therefore, the
use of glass powder and Nd power is advantageous when processing
the filter to have a complex shape.
Note that when manufacturing glass that includes neodymium, the
ratios by weight of silica (SiO.sub.2), an alkali metal compound
(Na.sub.2O+Li.sub.2O+K.sub.2O), an alkaline earth metal oxide
(CaO+SrO+BaO+MgO), and neodymium oxide (Nd.sub.2O.sub.3) were
respectively 63.9%, 13.7%, 13.7%, and 8.7%. The glass was fused at
1200.degree. C. and subsequently formed into a plate shape. Within
the alkali metal oxide, Na.sub.2O, Li.sub.2O, and K.sub.2O had the
same weight. Similarly, within the alkaline earth metal oxide, CaO,
SrO, BaO, and MgO had the same weight. The resulting plate glass
was then annealed for two hours at 1000.degree. C. under a flow of
nitrogen gas of 100 cc/minute. The filter characteristics in the
wavelength range from 570 nm to 590 nm were sharp after this
treatment.
A different method for manufacturing glass containing neodymium is
the sol-gel method described below. 30 g of a neodymium oxide
powder having a diameter of 7 .mu.M is mixed into a solution
containing 20 cc, 80 cc, and 80 cc respectively of tetraethyl
orthosilicate Si(OC.sub.2H.sub.5).sub.4, water, and ethanol, thus
yielding a mixed liquid. Several cubic centimeters of 0.01
mol/dm.sup.3 hydrochloric acid (or alternatively, nitric acid or
acetic acid) is then added to the mixed liquid. This mixed liquid
containing neodymium oxide powder is then turned into a gel. The
resulting gel is injected into a plate mold and dried for two hours
at 100.degree. C. After drying, the product is baked for one hour
at 800.degree. C. to manufacture plate glass containing neodymium.
A silicon alkoxide other than tetraethyl orthosilicate may also be
used.
Furthermore, as shown in FIG. 22, the absorption wavelength band
for the glass plate and the glass powder are roughly equal, whereas
the absorption wavelength band for the Nd powder is shifted in the
direction of longer wavelengths. Furthermore, the transmittance is
approximately the same for the glass plate in the directions of
both shorter and longer wavelengths of the absorption wavelength
band, whereas the transmittance differs between the directions of
shorter and longer wavelengths for the glass powder. Selectively
exploiting these different characteristics allows for adjustment of
the light emission characteristics of an LED lamp.
Modifications
(1) While the embodiment discloses the structure of an LED module,
the present invention is not limited to the above embodiment. For
example, the following modifications are possible.
FIGS. 24A through 24D show modifications to the structure of the
LED module.
In an LED module 5a, a translucent material 17 made of silicone
resin or the like is sandwiched between a translucent material 13
and a plate-shaped filter 16. The refractive index of the
translucent material 17 is equivalent to or higher than the
refractive index of the translucent material 13 and lower than the
refractive index of the filter 16. This structure enhances the
filter effect described with reference to FIGS. 19, 20, and 21A
through 21C.
An LED module 5b is an example in which an annular reflector
element 18 having with a reflective inner face is disposed on a
circuit board 11. A plate-shaped filter 16 is disposed on top of a
reflector element 18. With this structure, light emitted from the
LED light source towards the sides is reflected by the reflective
face toward the front. Consequently, the intensity of light at the
front of the LED lamp is increased.
An LED module 5c is an example of providing a translucent material
19 in a gap between an LED light source and a reflector element 18.
This structure increases the flux ratio, while also increasing the
intensity of light at the front of the LED lamp.
In an LED module 5d, a gap surrounded by a circuit board 11, a
filter 16, and a reflector element 18 is packed with translucent
material to form a translucent material 13.
Note that the filter may be formed by dispersing neodymium within
the translucent material 13, which is formed from silicone resin or
the like. In this case, the filter 16 is unnecessary.
When using the above sol-gel method to manufacture the translucent
material 13 with phosphor dispersed therein, a desired effect can
also be achieved by including neodymium. In this case, 30 g of a
neodymium oxide powder having a diameter of 7.mu.m is mixed into a
solution containing 20 cc, 80 cc, and 80 cc respectively of
tetraethyl orthosilicate Si(OC.sub.2H.sub.5).sub.4, water, and
ethanol, thus yielding a mixed liquid. A desired amount of phosphor
is further mixed therein. Several cubic centimeters of 0.01
mol/dm.sup.3 hydrochloric acid (or alternatively, nitric acid or
acetic acid) is then added to the mixed liquid. This mixed liquid
containing neodymium oxide and phosphor is then turned into a gel.
The resulting gel is injected into a plate mold and dried for two
hours at 100.degree. C. After drying, the product is baked for
three hours at 200.degree. C. to manufacture plate glass containing
neodymium oxide and phosphor. In this case as well, the filter 16
is not necessary. Note that a silicon alkoxide other than
tetraethyl orthosilicate may also be used.
(2) In the embodiment, the filter is a small piece of a plate, but
the present invention is not limited in this way. For example, the
following modifications are possible.
FIGS. 25A and 25B show modifications to the placement of the
filter. In an LED lamp 1a, the globe 6a itself contains neodymium
oxide, thus also functioning as a filter. An LED lamp 1b has a
filter layer 7, which includes neodymium oxide, covering the inner
surface of the globe 6. Alternatively, the filter layer 7 may cover
the outer surface of the globe 6.
(3) In the embodiment, the LED lamp is light-bulb shaped, but the
present invention is not limited in this way. For example, the
following modifications are possible.
FIG. 26 shows a modification to the structure of the LED lamp. An
LED lamp 1c is a substitute for a straight tube fluorescent lamp.
LED modules 5 are provided in a line inside a straight glass tube
8. At each end of the glass tube 8, a base 9 is provided to receive
power supplied to the LED modules 5.
(4) In the embodiment, only an LED lamp is disclosed, but the LED
lamp may be combined with a fixture and used as an LED illumination
device.
FIG. 27 shows the structure of an LED illumination device. An LED
illumination device 20 includes an LED lamp 1 and a fixture 21. The
fixture 21 includes a bowl-shaped reflector 22 and a socket 23.
Abase 3 of the LED lamp 1 is screwed into the socket 23.
(5) The embodiment describes an LED lamp used for general
illumination in places such as restaurants and stores that sell
merchandise. The present invention is not, however, limited in this
way. The appearance of illuminated objects may be of great
importance for medical equipment as well. As an example of such
medical equipment, the following describes an endoscope system.
FIG. 28 shows the structure of an endoscope system. An endoscope
system 30 includes a scope unit 31, a processor unit 32 connected
to the scope unit 31, and a display unit 33 connected to the
processor unit 32.
The scope unit 31 is provided with a lens 34, a CCD (Charge Couple
Device) image sensor 35 (hereinafter referred to as a CCD sensor),
an AFE (Analog Front End) 36, a CCD driver 37, a lens 38, and a
light guide 39. The AFE 36 includes a CDS (Correlated Double
Sampling) circuit, an AGC (Auto Gain Control) circuit, and an ADC
(Analog Digital Converter) circuit.
The processor unit 32 is provided with a signal processing unit 40,
a video signal generation unit 41, a control unit 42, an LED module
43, and an LED driver 44. The LED module 43 emits light through the
light guide 39 and the lens 38 in order to illuminate the area to
be photographed by the CCD sensor 35.
The display unit 33 is provided with an LCD (Liquid Crystal
Display) panel 45, and LCD driver 46, a backlight 47, and an LED
driver 49. The backlight 47 includes LED modules 48. The display
unit 33 displays the image photographed by the CCD sensor 35.
The doctor looks at the image displayed on the display unit 33 in
order to diagnose the inside of the patient's body. Therefore, it
is crucial for the colors in the image displayed on the display
unit 33 to have a natural appearance. In particular, body tissue
often appears red, making it crucial for not only middle colors but
also strong red to have a natural appearance.
FIGS. 29A and 29B are xy chromaticity diagrams indicating a
chromaticity range of colors reproducible by the display unit and
chromaticity ranges of various body tissues. FIG. 29A shows the
entirety of the ranges, whereas FIG. 29B is a magnified view of
portion A.
The range a1 is the chromaticity range bounded by the spectral
locus and the purple boundary.
The range a2 is an example of a chromaticity range of reproducible
colors when conventional LED modules are used in the backlight of
the display unit. A conventional LED module is a combination of a
blue LED and a yellow phosphor (YAG).
The range a3 is an example of a chromaticity range of reproducible
colors when the LED modules of the present invention are used in
the backlight of the display unit. The LED module of the present
invention includes a blue LED with a main emission peak in the
wavelength range from 440 nm to 460 nm, a green/yellow phosphor
with a main emission peak in the wavelength range from 500 nm to
595 nm, a red phosphor with a main emission peak in the wavelength
range from 600 nm to 690 nm, and a filter that reduces the spectral
radiation intensity of at least a portion of the wavelength range
from 570 nm to 590 nm.
The ranges b1-b7 are the chromaticity ranges of various body
tissues: b1 is for tendons, b2 for fascia, b3 for adipose tissue,
b4 for muscle tissue, b5 for nerves, b6 for arterial blood, and b7
for venous blood.
The red chromaticity is indicated by c when using a conventional
light source in the backlight of the display unit, by d1 when using
LED modules with a combination of a blue LED and a yellow phosphor
as the conventional light source, and by d2 when using a
cold-cathode fluorescent lamp as the conventional light source.
The red chromaticity is indicated by c2 and by c3 when using the
LED modules of the present invention in the backlight of the
display unit, with c2 representing a main emission peak of 626 nm
for the red phosphor, and c3 representing a main emission peak of
645 nm for the red phosphor.
As is clear, the chromaticity range of colors reproducible by the
display unit with conventional LED modules includes the
chromaticity ranges of tendons, fascia, adipose tissue, muscle
tissue, and nerves, but not for arterial blood and venous blood.
With such a display unit, arterial and venous blood appear
colorless (grey) within the image, making these types of blood
indistinguishable in terms of color. By contrast, the chromaticity
range of colors reproducible by the display unit with LED modules
of the present invention includes the chromaticity ranges of
tendons, fascia, adipose tissue, muscle tissue, nerves, and
arterial blood. Furthermore, depending on the emission peak of the
red phosphor, either a portion (626 nm) or the entirety (645 nm) of
the chromaticity range for venous blood is included. With this
display unit, the color of arterial blood differs from that of
venous blood in the image, thus making it possible to distinguish
between arterial blood and venous blood based on color.
Note that in order to represent the color of body tissue naturally
within the image, it is necessary not only to expand the
chromaticity range of colors reproducible by the display unit, but
also to increase the color rendering of the LED module that
illuminates the body tissue. If body tissue is illuminated with an
unnatural color, the color of the body tissue in the image will of
course appear unnatural, even if the chromaticity range of colors
reproducible by the display unit is expanded. Conversely, if the
LED module illuminating the body tissue is equivalent to the LED
module in a display unit with a wide chromaticity range of
reproducible colors, the colors of body tissue in the image will
have a natural appearance. Accordingly, adopting the LED module of
the present invention as the LED module illuminating the body
tissue achieves an endoscope system that can represent body tissue
naturally. In this case, specifically setting the main emission
peak of the red phosphor to be 626 nm or greater achieves an
endoscope system that allows for a distinction between arterial
blood and venous blood in images.
INDUSTRIAL APPLICABILITY
The present invention is useful for example in general
illumination.
REFERENCE SIGNS LIST
1, 1a, 1b, 1c LED lamp
2 body
3 base
4 distal end of body
5, 5a, 5b, 5c, 5d LED module
6, 6a globe
7 filter layer
8 glass tube
9 base
11 circuit board
12 blue. LED
13 translucent material
14 green/yellow phosphor
15 red phosphor
16 filter
17 translucent material
18 reflector element
19 translucent material
20 LED illumination device
21 fixture
22 reflector
23 socket
* * * * *