U.S. patent application number 14/735572 was filed with the patent office on 2015-10-01 for lighting apparatuses and led modules for both illumination and optical communication.
The applicant listed for this patent is EPISTAR CORPORATION. Invention is credited to Steve M. HONG, Min-Hsun HSIEH.
Application Number | 20150280824 14/735572 |
Document ID | / |
Family ID | 47021430 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150280824 |
Kind Code |
A1 |
HONG; Steve M. ; et
al. |
October 1, 2015 |
LIGHTING APPARATUSES AND LED MODULES FOR BOTH ILLUMINATION AND
OPTICAL COMMUNICATION
Abstract
Lighting apparatuses and LED modules capable of both
illumination and data transmission are disclosed. An exemplifying
lighting apparatus has a LED module and a modulator. The LED module
comprises a plurality of LED cells connected as a LED chain having
two conductive pads. The light emitted from the LED module is
visible. The modulator provides driving current to the LED module
to transmit data.
Inventors: |
HONG; Steve M.; (Hsinchu,
TW) ; HSIEH; Min-Hsun; (Hsinchu, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EPISTAR CORPORATION |
Hsinchu |
|
TW |
|
|
Family ID: |
47021430 |
Appl. No.: |
14/735572 |
Filed: |
June 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13089946 |
Apr 19, 2011 |
|
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14735572 |
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Current U.S.
Class: |
398/118 |
Current CPC
Class: |
H05B 45/37 20200101;
F21Y 2105/12 20160801; F21Y 2115/10 20160801; H01L 25/167 20130101;
F21V 33/00 20130101; F21Y 2105/10 20160801; H01L 2924/00 20130101;
H04B 10/516 20130101; H01L 2924/0002 20130101; H01L 33/62 20130101;
H04B 10/572 20130101; F21Y 2113/13 20160801; H01L 2924/0002
20130101; H04B 10/116 20130101 |
International
Class: |
H04B 10/116 20060101
H04B010/116; H04B 10/572 20060101 H04B010/572; H04B 10/516 20060101
H04B010/516; H01L 25/16 20060101 H01L025/16; H01L 33/62 20060101
H01L033/62 |
Claims
1. An LED module, comprising: a modulator; a first LED chain,
connected to the modulator, comprising a first group of LED cells
and configured to emit a first light, wherein the first light
comprises a digital data over a signal carrier; a driver
independent from the modulator in controlling an emission of light;
a second LED chain, connected to the driver, comprising a second
group of LED cells, and configured to emit a second light which is
independent from an emission of the first light; and a wavelength
conversion layer associated with the first LED chain and
disassociated with the second LED chain.
2. The LED module of claim 1, further comprising first conductive
pads connected to the first LED chain and second conductive pads
connected to the second LED chain, wherein the first conductive
pads and the second conductive pads share a common conductive
pad.
3. The LED module of claim 2, wherein the first LED chain comprises
a first-type contact layer, the second LED chain comprises a
second-type contact layer, the first-type and the second-type
contact layers are electrically coupled to the common conductive
pad.
4. The LED module of claim 2, wherein the first LED chain comprises
a p-type contact layer, the second LED chain comprises an n-type
contact layer, the p-type contact layer and the n-type contact
layer are electrically coupled to the common conductive pad under
which an insulating layer is formed.
5. The LED module of claim 1, wherein the second LED chain
comprises an LED cell having an area of not greater than 121
mil.sup.2.
6. The LED module of claim 1, wherein the first LED chain is
capable of emitting a color light which is different from that
emitted from the second LED chain.
7. The LED module of claim 1, wherein the first LED chain comprises
at least one LED cell capable of emitting a color light different
from that emitted from another LED cell in the second LED
chain.
8. The LED module of claim 1, wherein the second LED chain has less
LED cells than the first LED chain.
9. The LED module of claim 1, further comprising a substrate having
an area between 1.21*10.sup.2 and 1*10.sup.5 mil.sup.2.
10. The LED module of claim 1, wherein the signal carrier has a
frequency imperceptible to human eyes.
11. The LED module of claim 1, wherein the LED module is capable of
receiving data in a way of power line communication.
12. The LED module of claim 1, wherein the first LED chain
comprises a first LED, the second LED chain comprises a second LED,
wherein the second LED has an area greater than that of the first
LED.
13. The LED module of claim 1, wherein the first light has a
wavelength spectrum having a peak which is not affected by the
second light.
14. An LED module, comprising: a modulator; an LED module
configured to emit a light comprising a digital data over a signal
carrier by the modulator; and a wavelength conversion layer bonded
to the LED module.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of co-pending Application
Ser. No. 13/089,946, filed on Apr. 19, 2011, for which priority is
claimed under 35 U.S.C. .sctn.120, the entire contents of all of
which are hereby incorporated by reference.
BACKGROUND
[0002] The present disclosure relates generally to optical
communication and array-type light-emitting devices.
[0003] Light emitting diodes (LEDs) are an important class of
solid-state devices that convert electric energy to light. They
generally comprise an active layer of semiconductor material
sandwiched between two oppositely-doped cladding layers. When a
bias is applied across the cladding layers, electrons and holes are
injected into the active layer where electrons and holes recombine
to generate photons, or light. Recent advances in LEDs have
resulted in highly efficient light sources that surpass the
efficiency of filament-based light sources, providing light with
equal or greater brightness in relation to input power.
[0004] Disadvantage of conventional LEDs used for lighting
applications is that they cannot generate white light directly from
their active layers. Recently, two different ways have been
introduced to produce white light from conventional LEDs. One way
to produce white light from conventional LEDs is to combine
different wavelength of light from different LEDs. For example,
white light can be produced by combining the light from red, green
and blue LEDs or combining the light from blue and yellow LEDs. The
other way to produce white light is using yellow phosphor, polymer
or dye to downconvert portion of the light from a blue LED into
yellow light. A white LED is seemly produced because it
simultaneously emits both blue and yellow light, which combine to
provide white light.
[0005] Since white LEDs are developed, LEDs have widely used
because of their high durability, longevity, portability, low power
consumption, absence of harmful substances such as mercury, and so
forth. Often-seen applications of LEDs include white light
illumination, indicator lights, vehicle signal and illuminating
light, LCD backlight modules, projector light sources, outdoor
displays, and so forth. Nevertheless, other applications might use
LEDs to replace their light sources.
SUMMARY
[0006] Embodiments of the present invention disclose a lighting
apparatus capable of simultaneously providing illumination and data
transmission to a receiver. The lighting apparatus comprises an LED
module and a modulator. The LED module comprises a plurality of LED
cells connected as an LED chain having two conductive pads. The
light emitted from the LED module is visible. The modulator
provides driving current to the LED module to transmit data.
[0007] Embodiments of the present invention disclose an LED module,
comprising LEDs and conductive pads. A first group of the LED cells
is connected as a first LED chain, driven for illumination. A
second group of the LED cells is connected as a second LED chain
for data transmission. The conductive pads include a first pair of
conductive pads connected to the first LED chain and a second pair
of conductive pads connected to the second LED chain.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention can be more fully understood by the subsequent
detailed description and examples with references made to the
accompanying drawings, wherein:
[0009] FIG. 1 illustrates a broadcast system;
[0010] FIG. 2 exemplifies light apparatus 12a;
[0011] FIG. 3 shows the waveform of driving current I.sub.IN that a
modem provides to the LED module of FIG. 2;
[0012] FIG. 4 demonstrates a cross section view of LED cells 8a(1,
1) and 8a(1, 2), cutting along the dotted line AA' in FIG. 2;
[0013] FIG. 5 exemplifies another light apparatus;
[0014] FIG. 6 shows the waveform of driving current I.sub.IN and
I.sub.LIN that the modulator and the illumination driver of FIG. 5
provide respectively;
[0015] FIG. 7 exemplifies another light apparatus;
[0016] FIG. 8 demonstrates a cross section view of LED cells 8c(3,
1) and 8c(3, 2) in FIG. 7, cutting along the dotted line BB';
and
[0017] FIGS. 9-12 exemplify four light apparatuses.
DETAILED DESCRIPTION
[0018] The following embodiments are described in sufficient detail
to enable those skilled in the art to make and use the invention.
It is to be understood that other embodiments would be evident
based on the present disclosure, and that proves or mechanical
changes may be made without departing from the scope of the present
invention.
[0019] In the following description, numerous specific details are
given to provide a thorough understanding of the invention.
However, it will be apparent that the invention may be practiced
without these specific details. In order to avoid obscuring the
present invention, some well-known configurations and process steps
are not disclosed in detail.
[0020] One embodiment of the invention employs LED cells as a light
source to transmit digital information over a free space optical
data pathway at the same time when LED cells functions for
illumination. Transmission is accomplished by modulating or varying
the current flowing through LED cells.
[0021] FIG. 1 illustrates broadcast system 10 with light
apparatuses 12a and 12b according to one embodiment of the
invention. Light apparatuses 12a and 12b are powered by AC grid
power lines and optionally receive digital data over AC grid power
lines by way of power line communication. Each of light apparatuses
12a and 12b has an LED module with at least one LED chip. By
modulating the light emitted from the LED chips, each of light
apparatuses 12a and 12b transmits the digital data over the air to
receiver 14a or 14b. The modulation should be over a signal carrier
with an adequately-high frequency and be imperceptible by a human
eye.
[0022] Subject to other factors, the data transmission rate from
the AC power lines to receiver 14a or 14b is limited by the signal
bandwidth that the LED chips in light apparatuses 12a and 12b can
support. Input capacitance of each LED chip in light apparatuses
12a and 12b could strongly affect the bandwidth supported.
Hereinafter, input capacitance of an LED chain refers to the
capacitance measured from two conductive pads respectively
connected to n-type and p-type contact layers of the LED chain, by
means of small-signal response. The less input capacitance of an
LED chip, the broader bandwidth the LED chip can support.
[0023] FIG. 2 exemplifies light apparatus 12a. As shown in FIG. 2,
light apparatus 12a has modem 16 and LED module 19a including LED
chips 8a. Modem 16, powered by AC grid power lines, is the
combination of a demodulator which retrieves data carried from AC
grid power lines, and a modulator 17 which provides and modulates
driving current I.sub.IN to LED module 19a to transmit data over
the emitted light. Modulator 17 might include a converter
converting an AC source current to driving current I.sub.IN. The
light emitted from the LED chips 8a is a visible light, for example
a blue light having a wavelength spectrum around 440.about.480 nm,
a green light having a wavelength spectrum around 500.about.560 nm,
a green light having a wavelength spectrum around 500.about.560 nm,
a red light having a wavelength spectrum around 600.about.650 nm,
or white light. In the embodiment of FIG. 2, LED module 19a has two
LED chips 8a connected in series. For another embodiment, an LED
module might have only one LED chip.
[0024] As an example, LED chip 8a has LED cells 8a(1,
1).about.8a(3, 3), arranged as an LED array with 3 columns and 3
rows. Label WW(N, M) refers to the LED cell located at N.sup.th
column and M.sup.th row of LED chip WW. LED cells 8a(1,
1).about.8a(3, 3) are connected in series as an LED chain having
two conductive pads IN+ and IN-, which are located at two diagonal
corners of LED cells 8a(1, 1) and 8a(3, 3), respectively. The
physical orientation for each LED cell in 1.sup.st and 3.sup.rd
column is opposite to that of each LED cell in 2.sup.nd column. If
one LED cell in an LED chain is forward biased, all LED cells in
the LED chain are forward biased, and vice versa. In one
embodiment, LED cells 8a(1, 1).about.8a(3, 3) are epitaxial grown
on a monolithic substrate through MOCVD process and other
semiconductor process, such as sputtering, lithography, and etching
process, such that the active layers therein are formed at the same
time and made of substantially the same material. As the operation
voltage of LED chip 8a is the summation of the operation voltages
of individual LED cells, LED chip 8a is sometimes referred as a
high-voltage (HV) LED chip. The number of the LED cells of the LED
chip is around 3.about.80, or preferred 8-40, depending on the
operation voltage to be applied.
[0025] In order to provide the function of illumination, an LED
chip should have enough number of LED cells emitting at the same
time. LED cells connected in parallel could emit light at the same
time, but the input capacitance for the LED cells as a whole
increases as the number of the LED cells increases. Supposed that
there are K1 identical LED cells connected in parallel and each
individual LED cell has input capacitance of F farad, the
capacitance of the LED cells as a whole will be K1*F farad. As
mentioned before, increased input capacitance might reduce the
bandwidth and the data transmission rate, such that LED cells
connected in parallel are not suitable for data communication.
Nevertheless, LED cells connected in series as an LED chain emit at
the same time, and the input capacitance for the LED cells as a
whole decreases as the number of the LED cells connected in series
increases. The input capacitance for K1 identical LED cells as a
whole will be F/K1 farad if they are connected in series wherein
each individual one has input capacitance of F farad. Thus, an LED
chain is suitable for both illumination and data transmission. In
the embodiment of FIG. 2, a driven LED chain has a plurality of LED
cells connected in series, the number of the LED cells is around
3.about.80, or preferred 8-40.
[0026] There is another advantage that series connection surpasses
parallel connection. Each and every LED in an LED chain of an LED
chip will be driven with the same driving current even if there are
slight differences between the characteristics of the LED cells in
the LED chain. In other words, the LED cells in an LED chain of an
LED chip emit power evenly. LED cells connected in parallel acts
differently, however. Most of the driving current for the LED cells
connected in parallel crowds to the LED cell with the least
resistance, such that the LED cell with the least resistance emits
higher power in comparison with others, therefore downgrading the
reliability of the LED chip.
[0027] FIG. 3 shows the waveform of driving current I.sub.IN that
modem 16 could provide to LED module 19a of FIG. 2. Driving current
I.sub.IN substantially switches between a high current level and a
low current level back and forth. The low current level (of logic
0) is no less than 0 A and could be as low as 0 A, forcing LED
module 19a to stop emitting. The high current level (of logic 1)
drives LED module 19a to emit visible light. Within a clock cycle
time, a rising edge means data "1" while a falling edge means data
"0". This kind of encoding scheme is called Manchester coding, a
special case of binary phase shift keying. The data transmission
rate should exceed the frequency range perceivable by a human eye,
such that LED module 19a is seen by human eyes to illuminate
without flickering and provide constant intensity of light as being
driven by average current I.sub.BRT, which is the average of the
high and low current levels.
[0028] As an example, FIG. 4 demonstrates a cross section view of
LED cells 8a(1, 1) and 8a(1, 2), cutting along the dotted line AA'
in FIG. 2. A similar drawing has been published in FIG. 2 of US
Patent Application Publication 2010/0213474, whose entirety is
incorporated by reference. As shown in FIG. 4, LED cells 8a(1, 1)
and 8a(1, 2) are grown on a monolithic substrate 60, each having,
from bottom to top, n-type contact layer 62, n-type cladding layer
64, active layer 66, p-type cladding layer 68, and p-type contact
layer 70. A wavelength conversion layer 72 is optionally formed on
contact layer 70 to convert the light emitting from the active
layer. Two electrodes 76 and 74 are optionally formed (may be
omitted) on n-type contact layer 62 and p-type contact layer 70,
respectively. LED cells 8a(1, 1) and 8a(1, 2) are physically
separated on monolithic substrate by a trench between LED cells
8a(1, 1) and 8a(1, 2). An electric circuit layer 78 provides
electric connection between the n-type contact layer 62 of 8a(1,1)
and the p-type contact layer 70 of the adjacent LED cell, such as
8a(1, 2) to forma series connection. An insulator layer 80 is
formed under portion of electric circuit layer 78 to prevent
unwanted short circuits. In one embodiment, each of LED cells 8a(1,
1) to 8a(3, 3) occupies a cell area on the monolithic substrate 60
no more than 121 mil.sup.2. The monolithic substrate 60 has a
surface area, for example between 1.21*10.sup.2 to 1*10.sup.5
mil.sup.2.
[0029] Two conductive pads IN-, IN+ are provided for electric
connection between the LED chip 8a and an electric circuit outside
the chip through external wires. The two conductive pads IN-, IN+
are respectively formed on the monolithic substrate 60 outside the
array area for LED cells 8a(1, 1).about.8a(1, 3), and preferably at
different corners or borders of the LED chip 8a. The conductive
pads IN-, IN+ are electrically coupled to the LED cells
8a(1,1).about.8a(1,3) via the electric circuit layer 78 as in FIG.
4.
[0030] As LED cells 8a(1,1).about.8a(3,3) are epitaxial grown on
monolithic substrate 60 using MOCVD process and other semiconductor
process, such as sputtering, lithography, and etching process, the
compositions of the active layers 66 therein are substantially the
same to emit lights with the same or similar wavelength spectrum.
Nevertheless, wavelength conversion layers 72 may be different or
absent for some LED cells. For example, in one embodiment, all LED
cells 8a(1, 1).about.8a(3, 3) are white LED cells each having an
active layer emitting blue light and a wavelength conversion layer
downconverting the blue light into yellow light. In another
embodiment, some of LED cells 8a(1,1).about.8a(3,3) are white LED
cells each having a wavelength conversion layer downconverting the
blue light into yellow light, and others are blue LED cells having
a wavelength conversion layer downconverting the blue light into
red light. In another embodiment, some of LED cells
8a(1,1).about.8a(3,3) are white LED cells each having a wavelength
conversion layer and others are blue LED cells having no wavelength
conversion layer. In one embodiment, the wavelength conversion
layer is formed a layered structure bonded to the contact layer
through a glue bonding layer under chip process for the foregoing
embodiments. In another embodiment, the wavelength conversion layer
is formed by encapsulating the LED chip by an encapsulating
material containing a wavelength conversion material under
packaging process.
[0031] FIG. 5 exemplifies light apparatus 12b. LED module 19b is
controlled by controller 11 to provide both illumination and data
transmission. Similar with LED chip 8a of FIG. 2, LED chip 8b in
LED module 19b has LED cells 8b(1,1).about.8b(3,3), arranged as an
LED array on a monolithic substrate. LED chip 8b is slightly
different with LED chip 8a. While LED chip 8a of FIG. 2 has only
one LED chain with one pair of conductive pads IN+ and IN- as
inputs, LED chip 8b of FIG. 5 has two LED chains 22 and 24. The
number of LED cells in one LED chain is not restricted and one LED
chain might include only one LED cell as exemplified by LED chain
24, or more than one LED cell. LED chain 22 has a pair of
conductive pads LIN+ and IN+/LIN- while LED chain 24 has a pair of
conductive pads IN+/LIN- and IN-. It can be found conductive pad
IN+/LIN- is a common conductive pad connected to both the anode (or
the n-type contact layer) of LED chains 24 and the cathode (or the
p-type contact layer) of LED chain 22. Conductive pads LIN+, IN-,
and IN+/LIN- are provided for electric connection between the LED
chip 8a and an electric circuit outside the chip through external
wires. The conductive pads LIN+, IN-, and IN+/LIN- are respectively
formed on the monolithic substrate 60 outside the area of the LED
cells of LED chip 8b, and preferred at different corners or borders
of the LED chip 8b as shown in FIG. 5. The conductive pads LIN+,
IN-, and IN+/LIN- are electrically coupled to the LED cells via the
electric circuit layer 78 as in FIG. 4. For example, pad IN+/LIN-
is connected via electric circuit layer 78 to both a p-type contact
layer of LED chain 24 and a n-type contact layer of LED chain 22.
The pair of conductive pads LIN+ and IN+/LIN- is connected to
illumination driver 13 of controller 11 and the pair of conductive
pads IN+/LIN- and IN- is connected to modulator 17 of controller
11. FIG. 6 shows the waveform of driving current I.sub.IN and
I.sub.LIN respectively provided by modulator 17 and illumination
driver 13 of FIG. 5. The operation of modulator 17 is not detailed
here for brevity since it has been done in the paragraphs regarding
with FIGS. 2 and 3. It is comprehensive that LED chain 24 driven by
modulator 17 transmits data via the light it emits. Illumination
driver 13 of FIG. 5 provides driving current I.sub.LIN to LED chain
22. Driving current I.sub.LIN is almost a constant and conveys no
data as shown in FIG. 6, such that LED chain 22 only acts as a
lighting source for illumination. Accordingly, LED chip 8b has two
LED chains 22 and 24 where LED chain 22 is only for illumination
and LED chain 24 is for data transmission. In one embodiment, LED
chip 8b is formed on a monolithic substrate, each of LED cells
8b(1, 1) to 8b(3, 3) occupies a cell area on a monolithic substrate
no more than 121 mil.sup.2, and the number of LED cells in LED
chain 24 is smaller than that in LED chain 22. In another
embodiment, the area of one of the LED cell(s) in LED chain 24 for
data transmission is smaller than that in LED chain 22 for
illumination. In one embodiment, the area of one of the LED cell
(s) for data transmission is preferred no more than 121 mil.sup.2,
and the area of one of the LED cells for illumination is preferred
no more than 400 mil.sup.2.
[0032] In one embodiment, LED chains 22 and 24 emit light of
different colors. For example, LED cells in chain 22 comprises
white LED cells and LED cell 8b(3,3) in chain 24 is a blue LED
cell.
[0033] FIG. 7 exemplifies light apparatus 12c. Similar with LED
chip 8b of FIG. 5, LED chip 8c of FIG. 7 has two LED chains 26 and
28. LED chain 26 is only for illumination, driven via a pair of
conductive pads LIN+ and LIN-/IN- by illumination driver 13. LED
chain 28 is for data transmission, driven via a pair of conductive
pads IN+ and LIN-/IN- by modulator 17. The conductive pad LIN-/IN-
is electrically connected to both two n-type contact layers of LED
chains 26 and 28. In one embodiment, LED chip 8c is formed on a
monolithic substrate. FIG. 8 demonstrates a cross section view of
LED cells 8c(3, 1) and 8c(3, 2) in FIG. 7, cutting along the dotted
line BB'. As shown in FIG. 8, even though they are located in the
same column, LED cell 8c(3, 1), which belongs to LED chain 26, has
a cell orientation opposite to LED cell 8c(3, 2), which belongs to
LED chain 28.
[0034] It is unnecessary that the LED chain only for illumination
must shares a common conductive pad with the LED chain for data
transmission. FIGS. 9 and 10 exemplify light apparatuses 12d and
12e. In FIG. 9, LED chip 8d has LED chain 30 only for illumination
and LED chain 32 for data transmission. Conductive pads LIN+ and
LIN- for LED chain 30 are independent to conductive pads IN+ and
IN- for LED chain 32, while LED cell 8d(3, 1) has the same cell
orientation with LED cell 8d(3, 2). LED chains 30 and 32 are
electrically insulated on the monolithic substrate. In FIG. 10, LED
chip 8e has LED chain 34 only for illumination and LED chain 36 for
data transmission, while LED cell 8e(3, 1) has a cell orientation
opposite to LED cell 8e(3, 2).
[0035] FIG. 11 exemplifies light apparatus 12f. It is unnecessary
that LED cells in an LED module are all monolithically formed as an
array on a monolithic substrate. In FIG. 11, LED module 19f has
individual LED chips 8f1 to 8fn, where n is an integer. LED chips
8f1 to 8fn could be formed on different substrates individually and
together packaged on a submount, where the data transmitting speed
would be lower compared with the LED module as disclosed in the
foregoing embodiments using a monolithically-formed LED cell array
on a single chip. In one embodiment, LED chips 8f1 to 8fn are all
white LED chips. In another embodiment, LED chips 8f1 to 8fn
consist of red, green and blue LED chips. LED module 19f has two
conductive terminals TIN+ and TIN-, through which modulator 17
provides driving current I.sub.IN to LED cells 8f1 to 8fn to
transmit data.
[0036] FIG. 12 exemplifies light apparatus 12g. Similar with FIG.
11, LED module 19g of FIG. 12 has LED chips 8g1 to 8gn, where n is
an integer. LED chips 8g1 to 8g5 are grouped and connected as LED
chain 38, driven by illumination driver 13 and functioning only for
illumination. LED chips 8g6 to 8gn are grouped and connected as LED
chain 40, driven by modulator 17 for data transmission. The light
from LED chain 38 might be the same with or different to that from
LED chain 40. LED chips 8g1 to 8g5 of LED chain 38 or LED chips 8g6
to 8gn of LED chain 40 comprise at least one selected from blue
LED, green LED, red LED, and white LED chips. For example, LED
chips 8g1 to 8g5 of LED chain 38 consist of green and red LED chips
and LED chips 8g6 to 8gn consist of only blue LED chips. In one
embodiment, LED chain 38 provides visible light, and LED chain 40
provides invisible light. In view of noise immunity, it is
preferable that the wavelength spectrum of the light from LED chain
40 has a peak that is not affected by the intensity of the light
from LED chain 38.
[0037] All the previously-mentioned LED chains that function,
partially or fully, for illumination provide visible light.
Nevertheless, the previously-mentioned LED chains that function
only for data transmission could provide visible or invisible
light.
[0038] While the invention has been described by way of example and
in terms of preferred embodiment, it is to be understood that the
invention is not limited thereto. To the contrary, it is intended
to cover various modifications and similar arrangements (as would
be apparent to those skilled in the art). Therefore, the scope of
the appended claims should be accorded the broadest interpretation
so as to encompass all such modifications and similar
arrangements.
* * * * *