U.S. patent application number 09/397143 was filed with the patent office on 2001-11-29 for direct view lighting system with constructive occlusion.
Invention is credited to BAGWELL, RICHARD S., CROWLEY, GEORGE DAVID III, RAINS, JACK C. JR., RAMER, DAVID P..
Application Number | 20010046133 09/397143 |
Document ID | / |
Family ID | 26727966 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010046133 |
Kind Code |
A1 |
RAMER, DAVID P. ; et
al. |
November 29, 2001 |
DIRECT VIEW LIGHTING SYSTEM WITH CONSTRUCTIVE OCCLUSION
Abstract
A system utilizing direct-view illumination of selected regions
together with principles of constructive occlusion (diffuse
reflectivity in a mask and cavity structure) provides a tailored
radiation intensity distribution adapted to meet the requirements
of certain special applications. The direct illumination provides
high intensity illumination for certain desired regions. However,
some radiant energy from the system source(s) reflects and diffuses
within the volume between the mask and the cavity. The mask
constructively occludes the aperture of the cavity. The reflected
energy emerging from between the mask and cavity provides a desired
illumination, for example at a much lower intensity, for regions
not covered by the direct illumination. For example, in an
embodiment wherein the direct illumination provides light over
angles near the system horizon, the constructive occlusion in the
mask and cavity arrangement provides lower intensity illumination
in regions at higher elevation angles up to the system axis.
Inventors: |
RAMER, DAVID P.; (RESTON,
VA) ; RAINS, JACK C. JR.; (HERNDON, VA) ;
BAGWELL, RICHARD S.; (CHESTERFIELD, VA) ; CROWLEY,
GEORGE DAVID III; (CHEVY CHASE, MD) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
26727966 |
Appl. No.: |
09/397143 |
Filed: |
September 16, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09397143 |
Sep 16, 1999 |
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09050175 |
Mar 30, 1998 |
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5967652 |
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09050175 |
Mar 30, 1998 |
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08590290 |
Jan 23, 1996 |
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5733028 |
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Current U.S.
Class: |
362/298 ;
362/247; 362/343 |
Current CPC
Class: |
Y10S 362/80 20130101;
G01S 7/4816 20130101; G01S 17/66 20130101; G01S 17/42 20130101;
G01S 5/16 20130101; G01S 5/163 20130101 |
Class at
Publication: |
362/298 ;
362/343; 362/247 |
International
Class: |
F21V 007/00 |
Claims
What is claimed is:
1. A system for projecting electromagnetic radiation, comprising:
a) a base having a first defined area substantially facing a region
to be illuminated with the electromagnetic radiation, the first
defined area having a reflective characteristic with respect to the
electromagnetic radiation; b) a mask between the base and the
region to be illuminated at a predetermined distance from the
defined area of the base, said mask having a defined area
substantially facing the defined area of the base and having a
reflective characteristic with respect to the electromagnetic
radiation; c) a cavity formed in one of the defined areas, said
cavity comprising an inner surface with a substantially diffuse
reflective characteristic with respect to the electromagnetic
radiation and an opening, a perimeter of the opening of the cavity
forming an aperture, wherein the mask is positioned relative to the
base and configured so as to occlude electromagnetic radiation
emerging from the aperture of the cavity with respect to
illumination of the region; and d) a source configured to emit a
substantial first portion of the electromagnetic radiation directly
into a predetermined section of the region to be illuminated and to
emit a substantial second portion of the electromagnetic radiation
into the cavity, such that the direct radiation provides a
relatively high intensity illumination in the predetermined section
and the base, mask and cavity provide a tailored intensity
distribution of the second portion of the electromagnetic radiation
over another predetermined section of the region to be illuminated,
the tailored intensity distribution including a relatively low
intensity illumination.
2. A system as in claim 1, wherein the relatively high intensity
illumination is approximately an order of magnitude higher than the
relatively low intensity illumination.
3. A system as in claim 2, wherein the relatively low intensity
illumination is at or near the axis of the system, and the
predetermined section illuminated with the relatively high
intensity covers a range of angles substantially separated from the
axis of the system.
4. A system as in claim 3, wherein the range of angles approaches
angles perpendicular to the system axis.
5. A system as in claim 3, wherein the defined area of the base and
the defined area of the mask exhibit a highly diffuse reflectivity
with respect to the electromagnetic radiation.
6. A system as in claim 5, wherein the source emits visible light,
and the highly diffuse reflectivity is with respect to visible
light.
7. A system as in claim 3, wherein the base, the mask, the cavity
and the source are arranged so that the system illuminates a
predetermined area of a planar surface with a substantially uniform
intensity.
8. A system as in claim 1, wherein: the cavity is formed in the
base, and the defined reflective area of the mask faces toward the
aperture of the cavity; and the source is positioned between the
defined reflective area of the mask and the aperture of the
cavity.
9. A system as in claim 1, wherein: the cavity is formed in the
base, and the defined reflective area of the mask faces toward the
aperture of the cavity; and at least a portion of the source is
positioned within a volume of the cavity.
10. A system as in claim 1, further comprising a reflective
shoulder surrounding at least a substantial portion of the defined
reflective area of the base.
11. A system as in claim 10, wherein the shoulder has a
substantially diffuse reflective characteristic with respect to the
electromagnetic radiation.
12. A system as in claim 1, further comprising a reflective baffle
positioned between the mask and the inner surface of the
cavity.
13. A system as in claim 12, wherein the baffle comprises a planar
surface extending parallel to the aperture about an axis of the
cavity, aperture and mask.
14. A system as in claim 13, wherein the baffle further comprises
an annular surface, formed at an angle with respect to the planar
surface and extending from the planar surface to the inner wall of
the cavity.
15. A system as in claim 12, wherein the baffle comprises a
plurality of reflective walls extending radially outward from a
axis of the mask and cavity so as to divide a region between the
mask and the inner surface of the cavity into sections.
16. A system as in claim 15, wherein the baffle comprises four
walls and the walls divide the region between and the inner surface
of the cavity the mask into quadrants.
17. A lighting system, comprising: a cavity having a diffusely
reflective inner surface and an aperture; a mask positioned outside
the cavity at a distance from the aperture, the mask having a
reflective surface optically facing the aperture, the mask
constructively occluding the aperture of the cavity with respect to
a field of intended illumination, such that light reflected between
the mask and cavity and emerging from a gap between the mask and
the aperture illuminates a substantial portion of the field of
intended illumination with a desired intensity distribution
pattern; and a source of light positioned between the mask and the
inner surface of the cavity so as to emit a first portion of light
for diffuse reflection between the mask and the cavity and thereby
produce the illumination with the desired intensity distribution,
the source also emitting a substantial second portion of light
directly into a predetermined section of the field of intended
illumination, to provide a desired higher intensity distribution in
said predetermined section.
18. A lighting system as in claim 17, wherein the predetermined
section of the field of intended illumination covers a range of
angles approaching a horizon of the lighting system, the
substantial portion of the field of intended illumination light
covers a range of angles approaching a system axis substantially
perpendicular to the horizon of the lighting system.
19. A lighting system as in claim 17, wherein the mask, the cavity
and the source are arranged so that the system illuminates a
predetermined area of a planar surface with a substantially uniform
light intensity.
20. A lighting system as in claim 17, further comprising a
reflective shoulder surrounding a substantial portion of the
aperture of the cavity.
21. An airport lighting system, comprising: a cavity having a
diffusely reflective inner surface and an aperture; a shoulder,
having a reflective surface characteristic, surrounding at least a
portion of the aperture of the cavity; a mask positioned outside
the cavity at a distance from the aperture, between the aperture
and a region to be illuminated, the mask having a reflective
surface facing toward the aperture; a source of radiant light
energy positioned between the mask and the aperture, wherein: the
mask is sufficiently spaced from the base cavity such that the
source directly emits a substantial first portion of the radiant
light energy into a first predetermined section of the region to be
illuminated adjacent to a horizon of the system with a relatively
high intensity, the source emits a second portion of the radiant
light energy into the cavity, and the reflective surface of the
mask constructively occludes the aperture of the cavity so that the
system radiates the second portion of the radiant light energy with
a tailored intensity distribution to thereby illuminate a second
predetermined section of the region to be illuminated at higher
elevations above the horizon with a relatively lower intensity.
22. A system as in claim 21, wherein the relatively high intensity
illumination comprises illumination approximately an order of
magnitude higher than at least some of the relatively low intensity
illumination.
23. A system as in claim 21, wherein the illumination at the higher
order of magnitude covers a range of elevation angles from the
horizon of the system up to at least 6.degree. above the horizon of
the system.
24. A system as in claim 23, wherein the relatively low intensity
illumination covers a range of angles about an axis of the mask and
cavity.
25. A system as in claim 21, wherein the source comprises at least
one light emitting diode.
26. A system as in claim 25, wherein the at least one light
emitting diode comprises a plurality of light emitting diodes
arranged about an axis of the mask and cavity to emit the first
portion of the radiant light energy radially outward from the
axis.
27. A system for projecting electromagnetic radiation with a
tailored intensity distribution having a high intensity portion in
a first angular region of an area to be illuminated and a low
intensity portion in a second angular region of the area to be
illuminated, the system comprising: a diffusely reflective cavity
with a aperture; a mask positioned outside the cavity so as to
constructively occlude the aperture with respect to at least the
second angular region, the mask having a reflective surface facing
toward the aperture; and means for directly illuminating the first
angular region with electromagnetic energy to provide the high
intensity portion of the illumination distribution and for
supplying electromagnetic radiation into the cavity to provide the
low intensity portion of the illumination distribution.
28. A system for projecting electromagnetic radiation as in claim
27, wherein the means comprises a source of electromagnetic energy
positioned between the reflective surface of the mask and an inner
surface of the cavity in such a manner as to directly illuminate
the first angular region and to supply at least some
electromagnetic radiation into the cavity.
29. A system as in claim 28, wherein the source comprises a
plurality of light emitting diodes arranged about an axis of the
cavity and mask, each light emitting diode being oriented to emit
light for the direct substantial illumination outward from the
axis.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to systems for illuminating a
desired area with electromagnetic radiation, such as visible or
infrared light, with a desired intensity distribution, using a
combination of direct radiation over a portion of the desired area
together with constructive occlusion to fill in other regions of
the desired area. In one type of visible lighting system, for
example, an embodiment of the invention uses direct illumination to
provide relatively high intensity illumination in regions near the
system horizon for a full circle around the system. The exemplary
embodiment utilizes principles of constructive occlusion to provide
a lower intensity illumination for higher elevation regions up to
the vertical axis of the system.
BACKGROUND
[0002] Radiant or electromagnetic energy emitters and distributors
find a wide range of applications in modem society. Visible
illumination systems, for example, illuminate areas and surfaces to
enable use by personnel even though natural ambient lighting might
be insufficient. Infrared illumination is a critical component of
many night-vision technologies. Other lighting devices provide
guidance or warnings, for example to enable pilots to locate the
edges of runways or taxiways, to illuminate emergency exit paths,
to visibly indicate the emergency, etc.
[0003] Different applications of radiant energy illumination
systems require different performance characteristics. For example,
a visible illumination application might require that the lighting
system provides a desired minimum intensity over a flat surface of
specified dimensions about an axis of the lighting system, at a
known distance from the system along its axis. Simple radiation
sources, such as light emitting diodes (LEDs) or light bulbs with
reflectors and/or lenses typically provide a high intensity
radiation in regions close to the axis, but the intensity drops of
quickly at angles approaching the horizon. On an illuminated
surface, the intensity is not uniform. To provide a desired
illumination at edges of a design footprint, the source often will
emit substantially higher amounts of radiation than necessary along
the axis.
[0004] Prior attempts to provide desired intensity distributions
have involved complex arrangements of sources, lenses and
reflectors. These complex arrangements tend to be relatively
expensive and sensitive to problems of misalignment, which limits
ruggedness and durability.
[0005] As another example of a difficult lighting application,
consider an airport lighting system. The regulatory authority
requires a high intensity illumination for regions near the
horizon, such as from the horizon up to an elevation of about
6.degree.. The airport light must also emit some light at higher
elevations, including along the vertical axis; however, the
intensity required at higher elevations may be an order of
magnitude lower than that near the horizon. Existing blue taxiway
lights and other runway lights utilize conventional light-bulb
technologies. Such lamps do meet the requirement for illumination
at the horizon as well as illumination above, although they tend to
over illuminate areas at high elevations above the horizon, in
order to provide adequate intensity at all necessary angles. As
such, they tend to consume more power than is necessary. More
importantly, the lamp burns out and must be replaced every 2000
hours or so.
[0006] Efforts are underway to develop a runway/taxiway lighting
system utilizing LEDs, because of the long life of such light
sources (hundreds of thousands of hours). However, to achieve the
necessary coverage with adequate intensity, LED-based systems have
used a complex matrix with a large number LEDs. For example,
horizontal LEDs might irradiate low elevation regions, but
additional sets of LEDs directed to higher elevations and one or
more vertically directed LEDs are needed to fill-in various
portions of the field of illumination. Examples of such systems
have included as many as 40-60 LEDs. As a result, the LED-based
system becomes quite expensive to construct and draws an inordinate
amount of electrical power.
[0007] U.S. Pat. No. 5,733,028 issued Mar. 31, 1998 to Ramer et al.
discloses a number of embodiments of illumination systems that
utilize constructive occlusion. With this technology, a mask
occludes an active optical surface, typically a Lambertian surface
formed by the aperture of a diffusely reflective cavity, in order
to distribute radiant energy with a tailored intensity
distribution. The disclosure there emphasizes uniformity of the
intensity distribution, for example with respect to angles
extending over a hemispherical radiation pattern. Adjustment of the
parameters of the constructive occlusion system enables the system
designer to tailor the system performance to a wide range of
applications. Constructive occlusion typically emphasizes
distribution based on multiple diffuse reflections within a mask
and cavity system. Careful selection of the system parameters can
adapt the constructive occlusion system to meet the requirements of
many diverse illumination applications.
[0008] However, a need still exists for radiant energy or
electromagnetic emission and distribution systems, which can
satisfy certain extreme requirements in differences in intensity
distribution. Such systems must be relatively simple in structure,
to minimize cost and maximize durability. Also, such systems should
be able to achieve a desired intensity distribution, with large
variations in power at different angles of illumination, without
requiring excessive input power or over illumination at any
particular angle, to thereby maximize efficiency.
DISCLOSURE OF THE INVENTION
[0009] To meet the above stated needs and objectives, the
inventions combine direct illumination from a source with
illumination provided by constructive occlusion techniques. Such a
combination of different types of illumination can precisely
satisfy design requirements of more than an order of magnitude
difference in illumination intensities in different segments of an
intended region of illumination. The direct illumination from the
source provides high intensity illumination for certain desired
regions. Some radiant energy from the source also diffuses and
reflects between the mask and cavity of the constructive occlusion
system. The parameters of the mask and cavity are such that radiant
energy processed by those elements provides a tailored intensity
distribution, including a predetermined low intensity illumination
in a region not covered by the direct illumination.
[0010] In one aspect, the inventions relate to systems for
projecting electromagnetic radiation, such as visible light. Such a
system includes a base having a first defined area substantially
facing a region to be illuminated with the electromagnetic
radiation. This area of the base has a reflective characteristic
with respect to the electromagnetic radiation. The system also
includes a mask. The mask is positioned between the base and the
region to be illuminated at a predetermined distance from the
defined area of the base. The mask also has a defined area,
substantially facing the area on the base, which has a reflective
characteristic with respect to the electromagnetic radiation. One
of the defined areas has a cavity. The inner surface of the cavity
has a substantially diffuse reflective characteristic with respect
to the electromagnetic radiation. The mask occludes electromagnetic
radiation emerging from an aperture of the cavity. The inventive
system also includes a source. The source emits a substantial first
portion of the electromagnetic radiation directly into a
predetermined section of the region to be illuminated. The source
also emits a substantial second portion of the electromagnetic
radiation into the cavity. The direct radiation provides a
relatively high intensity illumination in the predetermined
section, whereas the base, mask and cavity provide a tailored
intensity distribution of the second portion of the electromagnetic
radiation over another predetermined section of the region to be
illuminated.
[0011] The second portion of the electromagnetic radiation provides
a relatively low intensity illumination over at least a portion of
the second illuminated section. Many applications of the system
actually provide an intensity of the direct illumination that is an
order of magnitude higher than the lowest desired intensity in the
section of tailored illumination covered by the constructive
occlusion.
[0012] Several of the preferred embodiments provide the low
intensity illumination in regions about an axis of the mask and
cavity system. In such cases, the direct, high intensity
illumination covers angles relatively far-off the axis. For
example, the system may provide the high intensity at angles
directed towards distant edges of a wide planar surface, which is
uniformly illuminated by the system. Other exemplary embodiments
provide the high intensity illumination at angles approaching the
system horizon.
[0013] The inventive system may utilize a variety of reflective
materials. Preferred embodiments utilize materials providing
diffusely reflective surfaces on the elements of the constructive
occlusion system. The preferred embodiments of the mask and cavity
system also include a reflective shoulder, formed around a portion
or around the entire aperture of the cavity. The system may also
include a reflective baffle, in the region between the mask and the
cavity surface, to reflect additional light into certain regions of
the desired field of illumination, typically at relatively large
angles with respect to the axis of the mask and cavity.
[0014] Another inventive aspect relates more specifically to an
airport lighting system, designed to meet the particular
requirements for airport lighting. This system includes a cavity
with a diffusely reflective inner surface. A reflective shoulder
surrounds at least part of the aperture of the cavity. The system
also includes a mask. The mask is outside the cavity at a distance
from the aperture, between the aperture and a region to be
illuminated. The surface of the mask facing toward the aperture is
reflective. The system also includes a source of radiant light
energy. The source is positioned between the mask and the aperture,
for example near the reflective surface of the mask. The mask is
sufficiently spaced from the aperture of the cavity such that the
source directly emits a substantial first portion of its radiant
light energy into a region adjacent to a horizon of the system.
This direct emission provides a relatively high intensity
illumination. The source emits a second portion of its radiant
light energy into the cavity. The reflective surface of the mask
constructively occludes the aperture of the cavity, so that the
system radiates the second portion of the radiant light energy into
a region at higher elevations above the horizon, but with a
relatively lower intensity distribution.
[0015] Such an airport lighting system can efficiently provide high
intensity illumination near the horizon, for example, from the
horizon up to angles of at least 6.degree.. Such systems also
efficiently satisfy the requirements for lower intensity
illumination at higher elevation angles. A preferred embodiment
utilizes LEDs as the light source. Such embodiments typically
include a series of LEDs arrange in a ring, with the LEDs facing
outward to radially emit the direct illumination energy into the
regions near the horizon. The inventive system utilizes far fewer
LEDs, when compared to prior attempts to provide airport lighting
using LEDs. Consequently, the cost of the system as well as the
power consumption (one cost of operating the system) are much
lower.
[0016] Another inventive aspect relates to a system for projecting
electromagnetic radiation with a tailored intensity distribution.
The distribution includes a high intensity portion in a first
angular region of an area to be illuminated and a low intensity
portion in a second angular region of the area to be illuminated.
This system includes a diffusely reflective cavity with an
aperture. A mask outside the cavity constructively occludes the
aperture with respect to at least the second angular region. The
mask has a reflective surface facing toward the aperture. The mask
and cavity provide the low intensity portion of the illumination
distribution. The inventive system also includes means for directly
illuminating the first angular region with electromagnetic energy
to provide the high intensity portion of the illumination
distribution and for supplying electromagnetic radiation into the
cavity.
[0017] Additional objects, advantages and novel features of the
invention will be set forth in part in the description which
follows, and in part will become apparent to those skilled in the
art upon examination of the following or may be learned by practice
of the invention. The objects and advantages of the invention may
be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The drawing figures depict the present invention by way of
example, not by way of limitations. In the figures, like reference
numerals refer to the same or similar elements.
[0019] FIG. 1 is a cross-sectional view of a simple embodiment of
an illumination system utilizing direct radiation in combination
with constructive occlusion, in accord with the principles of the
present invention.
[0020] FIG. 2 is a cross-sectional view of another simple example
of an illumination system in accord with the invention.
[0021] FIG. 3 is an approximation of an illumination intensity
distribution graph of a system, such as that of FIG. 2, combining
direct illumination with illumination by constructive occlusion to
provide uniform illumination of a planar surface.
[0022] FIG. 4 is a line drawing of a perspective view of an airport
lighting system combining direct view with constructive occlusion,
in accord with the present invention.
[0023] FIG. 5 is a line drawing of a partial, exploded view of the
system of FIG. 4, showing the LED light sources, the underside of
the mask and the cavity, but with the shoulder omitted for ease of
illustration.
[0024] FIG. 6 is a line drawing of an isometric view of another
airport lighting system in accord with the present invention.
[0025] FIG. 7 is a top plan view of the lighting system of FIG.
6.
[0026] FIG. 8 is a line drawing of an isometric view of the
shoulder and lenses of the system of FIG. 6.
[0027] FIG. 9 is an approximation of an illumination intensity
distribution graph of an illumination system, such as shown in
either FIG. 4 or FIG. 6.
[0028] FIG. 10 is a cross-sectional view of an alternate embodiment
of the invention combining constructive occlusion with direct view
through an aperture of the mask.
[0029] FIG. 11 illustrates another embodiment of the invention,
with a "kicker" plate or baffle within the cavity.
[0030] FIG. 12 illustrates another embodiment of the invention,
with a baffle formed of radially extending walls within the
cavity.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The present invention utilizes principles of constructive
occlusion (diffuse reflectivity in a mask and cavity structure)
together with direct-view illumination of selected regions, to
tailor radiation intensity distribution to the requirements of
certain special applications. The direct illumination provides high
intensity illumination for certain desired regions, for example at
elevation angles near the horizon or directed to edges of a wide
planar area to be illuminated. Some light from the system source(s)
reflects and diffuses within the volume between the mask and the
cavity. The mask constructively occludes the aperture of the
cavity. The parameters of the mask and the cavity are selected such
that the reflected light emerging from between the mask and the
cavity provides a desired illumination, for example at a much lower
intensity, for regions not covered by the direct illumination. In
an embodiment wherein the direct illumination covers angles near
the horizon, for example, the constructive occlusion provides lower
intensity illumination in regions at higher elevation angles. The
inventive systems may provide a variety of other intensity
distributions, for example, to facilitate a uniform distribution
over a particularly wide planar target surface.
[0032] The combination of direct view illumination with
constructive occlusion enables the designer to precisely tailor the
illumination system to the needs of a particular application. As a
result, the designer need not over-radiate one area to meet the
requirements for radiation in another area. Consequently, the
system provides particularly high efficiencies and enables the use
of lower power and/or smaller or fewer sources of radiant energy.
The illuminating systems are relatively simple in design, making
the inventive devices relatively cheap to manufacture as well as
more durable than prior systems designed to meet similar
application requirements. The invention also enables the use of
more modem, dependable sources, such as LEDs.
[0033] Those skilled in the art will recognize that the principles
of the present invention are applicable to distribution of various
forms or wavelengths of radiant energy or electromagnetic
radiation. The preferred embodiments relate to illumination with
visible light, and the following discussion will concentrate on
discussion of lighting systems, although clearly the invention
encompasses radiation of other forms of electromagnetic energy.
[0034] FIG. 1 depicts a first, simple embodiment of a light
distributor apparatus 11, for projecting light with a tailored
intensity distribution. The light distributor 11 includes a
disk-shaped base 13 having a cavity 15 formed in its upper side,
surrounded by a flat, ring-shaped shoulder 17. A disk-shaped mask
19 is disposed between the cavity aperture 23 and the field to be
illuminated.
[0035] In many embodiments, the cavity 15 comprises a substantial
segment of a sphere. For example, the cavity may be hemispherical.
However, the cavity's shape is not of critical importance. A
variety of other shapes may be used. For example, half-cylindrical
cavities having a square or rectangular aperture or even having a
nearly linear aperture with a narrow rectangular opening are
contemplated for certain specific applications requiring a more
rectangular illumination footprint. Practically any cavity shape is
effective, so long as it has a diffuse reflective inner surface. A
hemisphere is preferred for the ease in modeling its azimuthal
symmetry and for its ease in construction. In illustrated
embodiments, the base is circular although other shapes may be
used.
[0036] The system 11 may be oriented in any desired manner to
facilitate illumination of a particular target area, region or
surface. In the orientation shown, the system 11 would provide
light outwardly and generally upward above the system, for example
to provide guidance on an airport taxiway. Inverted, the system 11
could be mounted on a ceiling or lamppost to illuminate the floor
or the ground. Turned to either side, the system might illuminate a
design or decoration on a wall or provide illumination along an
emergency exit path.
[0037] The mask 19 is positioned between the base 13 and the target
area, region or surface to be illuminated. As such, the mask 19 is
outside of the cavity 15. For example, in the orientation shown,
the mask 19 is above the aperture 23 of the cavity 15 in the base
13. A source 21 emits electromagnetic radiation, for example as
visible light. The system may include a variety of different types
of sources, including light bulbs, one or more LEDs, and one or
more optical fibers coupled to remote light generation components.
In the example, shown the source is an idealized spherical source
emitting radiation in virtually all directions.
[0038] In this first embodiment, the base 13 and the mask 19
preferably are formed of a suitable diffusely reflective material
such as Spectralon.RTM., which is a highly reflective polymeric
block material manufactured and sold by Labsphere, Inc., of North
Sutton, N.H. This material is easily machined and very durable, and
it provides a highly efficient Lambertian surface having a
reflectance of more than 99%, for visible and near-infrared
wavelengths. A Lambertian surface emits light with substantially
uniform intensity in all directions.
[0039] Alternatively, the base 13 and the mask 19 could be
constructed of a suitable base material of, for example, aluminum
or plastic, with a coating of a diffuse reflective material such as
barium sulfate or Spectralon on the appropriate surfaces. Other
suitable materials, though less effective than the diffuse
reflective materials identified above, include quasi-diffuse
reflective materials, such as gloss white paint. The use of such
materials provides improved performance over prior light
distributors.
[0040] For protection, the base preferably is encased in a plastic
or metal housing (not shown). A transparent dome (also not shown)
may be formed of a suitable material such as Pyrex.RTM..
[0041] The light source 21 emits some light into the base cavity
15, and this light is redirected outwardly by multiple diffuse
reflections from the base and the mask, as discussed more later. In
accord with the invention, the source is positioned between the
mask 19 and the cavity 15 in such a manner that it also emits a
substantial portion of radiation into a predetermined region within
the area of desired illumination. For this purpose, the source 21
is mounted in the region between the aperture 23 of the cavity 15
and the surface of the mask 19 facing toward the aperture. In the
example of FIG. 1, the source is mounted just below the facing
surface of the mask 19. In such an embodiment, the edges of the
mask 19 and the base 13 limit the range of angles of direct
radiation, e.g. as shown diagrammatically by the dotted line arrows
L1.
[0042] In accord with the invention, the region of direct
illumination is substantial. Although the precise angular width of
this region will vary between different applications, in preferred
embodiments, the range of direct illumination may be as little as
60 but is often at least 15.degree. and may be around 30.degree..
Because the source 21 emits light directly into this region, the
intensity in this region of direct view illumination is relatively
high.
[0043] The invention encompasses emitting the direct illumination
in different segments of the field of illumination of the inventive
systems, as discussed more later. The embodiment of FIG. 1 provides
the direct view illumination into the region of low elevation, for
example from the horizon up to about 15.degree. above the horizon,
in the orientation shown. In this embodiment, the direct
illumination covers the circular region from the system horizon up
to some specific limiting elevation angle, in this case defined by
the lower edge of the mask 19. Although not shown, the direct view
illumination may be limited so as to apply only to certain sides or
segments of the field of view around the location of the lighting
fixture.
[0044] As noted, the source 21 also emits a substantial portion of
its radiant energy in directions that cause the light to impact on
the diffusely reflective surfaces of the mask 19, the cavity 15 and
the shoulder 17. The light impacting on the surfaces of the mask
and cavity diffuse and redirect the light, typically so that the
light reflects and diffuses many times within the space between
mask and cavity before emerging from the gap between the outside
lower edge of the mask 19 and the edge or rim of the aperture of
the cavity 15. FIG. 1 shows two examples of light rays L2 from the
source 21 reflected between the underside of the mask 19 and the
surface of the cavity 15. As shown, a substantial portion of the
diffusely reflected light emerges from the system at higher angles
than that emitted for direct illumination.
[0045] For purposes of constructive occlusion, the base 13 may be
considered to have an active optical area, preferably exhibiting a
substantially Lambertian energy distribution. Where the cavity is
formed in the based, for example, the planar aperture 23 formed by
the rim or perimeter of the cavity 15 forms the active surface with
substantially Lambertian distribution of energy emerging through
the aperture. Although not shown, if the cavity were formed on the
underside of the mask, and the surface of the base was a flat
diffusely reflective surface, the active area on the base would
essentially be the mirror image of the cavity aperture on the base
surface.
[0046] In accord with the invention, the mask 19 constructively
occludes a portion of the optically active area of the system with
respect to the field of illumination. In the example of FIG. 1, the
optically active area is the aperture 23 of the cavity 15;
therefore the mask 19 occludes a substantial portion of the
aperture 23, including the portion of the aperture on and about the
axis of the mask and cavity system. The relative dimensions of the
mask 19 and aperture 23, for example the relative diameters or
radii in the circular embodiment, as well as the height of the mask
19 above or away from the aperture 23, control the constructive
occlusion performance characteristics of the light distributor
system 11.
[0047] Certain combinations of these parameters produce a
relatively low but uniform intensity with respect to angles of
emission, over a wide portion of the field of view about the system
axis (vertical in FIG. 1), covered principally by the constructive
occlusion. The areas covered by the direct illumination, however,
receive approximately an order of magnitude higher intensity
illumination than the minimum of the illumination by constructive
occlusion. Other combinations of size and height as well as the
angle of direct lighting formed between the perimeter of the cavity
and the lower edge of the mask, for example, result in a system
performance that is uniform with respect to a wide planar surface
perpendicular to the system axis at a fixed distance from the
aperture.
[0048] The embodiment of FIG. 1 will typically produce high
intensity illumination at angles approaching the horizon, or stated
another way, at angles approaching 90.degree. from the axis of the
system. Systems with such an intensity distribution satisfy the
requirements of a number of different applications, including
emergency pathway lighting, enunciators for signaling an emergency,
and airport lighting for runways and taxiways. Specific embodiments
developed for airport lighting are described in detail below, with
regard to FIGS. 4-9.
[0049] As noted, the first embodiment may produce high intensity
illumination at angles approaching the horizon with lower intensity
illumination at higher angles up to and including the axis of the
system. The inventive structures, however, may produce other types
of tailored intensity distributions. For example, in the embodiment
of FIG. 2, the source 21' is lower in the system 11', so that the
range of direct illumination becomes somewhat elevated above the
horizon. The base, 13, cavity 15 and mask 19 are otherwise similar
to those shown in FIG. 1 and described above. As such, the system
11' provides similar illumination by the operation of constructive
occlusion but provides the higher intensity direct illumination
over a substantial range of angles that is somewhat more
elevated.
[0050] Specifically, in the second embodiment, the source 21' emits
a substantial amount of light at appropriate angles for direct
illumination. The edges of the mask 19 and the perimeter of the
cavity 15 limit the range of angles of direct radiation in the
system 11', e.g. as shown diagrammatically by the dotted line
arrows L3.
[0051] The source 21' also emits a substantial portion of its
radiant energy in directions that cause the light to impact on the
diffusely reflective surfaces of the mask 19, the cavity 15 and the
shoulder 17. Again, the light impacting on the surfaces of the mask
and cavity diffuse and redirect the light within the space between
mask and the cavity surface. After one or more such reflections
within the system, this portion of the illumination energy emerges
from the gap between the outside lower edge of the mask 19 and the
edge or rim of the aperture 23 of the cavity 15, as shown for
example by the light rays L4. A substantial portion of the
diffusely reflected light emerges from the system at angles that
are still higher than that emitted for direct illumination.
[0052] The light distributor of FIG. 2 could be designed to produce
a uniform intensity distribution over the area of some surface,
such as a planar surface. With respect to angle of emission from
the distributor 11', the intensity must be higher in angular
regions away from the axis, compared to the intensity in regions
nearer the axis. The regions of high intensity may not need to
extend to the horizon, but only to an angular region encompassing
the desired area of illumination.
[0053] FIG. 3 is graph depicting an approximation of the intensity
vs. angle of emission curve, characteristic of the performance of a
light distributor constructed as shown in FIG. 2. To achieve a
desired planar uniformity of illumination, the distribution curve
as a function of angle from the axis takes the shape of a bat-wing.
The illumination device does produce some illumination in the
region about the axis (centered around the 0.degree. angle), mainly
from light from the shoulder 17 and the segment of the cavity 15
visible between the edge of the mask 19 and the aperture 23, when
viewed from a far distance along the system axis. However, the
intensity in this angular region is relatively low. As the angle
increases toward 90.degree. in either direction, the intensity
actually increases due to the dimensions of the aperture and mask.
As the angle increases still further, the intensity continues to
increase due to the light directly irradiated from the source 21.
After a certain angle, the edge of the aperture blocks direct
radiation from the source, and the illumination intensity drops off
again. For some further range of angles, there is still some
illumination, for example provided by light diffused and reflected
outward from the shoulder 17 and then by light diffused and
reflected from the side surfaces of the mask 19. The illumination
intensity falls to 0 at some angle before reaching the horizon in
the region of .+-.90.degree..
[0054] Inventive lighting systems, providing planar uniformity of
illumination, find many applications. For example, such systems are
advantageous in outside lighting systems, e.g. in parking lots and
the like. In such applications, a lighting fixture constructed in
accord with the invention provides a uniform illumination over a
relatively wide footprint. Typically, the size of a lighting area
or footprint is expressed in terms of multiples of "pole-heights,"
which is the distance of the fixture from the illuminated surface.
The use of direct illumination at outer angles, such as provided in
the system of FIG. 2, may extend the area of uniform illumination a
full pole-height or more outward from the point of intersection
with the axis.
[0055] In embodiments of the inventive system, at a minimum, the
interior surface of the cavity is diffusely reflective, and the
surface of the mask facing toward the active area of the base is
reflective (preferably diffusely reflective). The surface of the
shoulder typically is reflective; however, the precise type
reflectivity may be varied to meet different application
requirements. In many applications, the shoulder is diffusely
reflective, but the shoulder surface may have a specular
reflectivity for some applications. For other applications,
different sections of the shoulder may have different types of
reflectivity. For some applications, the shoulder width may be
minimal, or the shoulder may be eliminated entirely.
[0056] FIGS. 4 and 5 show a first embodiment of the invention using
LEDs, which is particularly useful in airport lighting systems for
runways or taxiways. At extreme off-axis regions, the direct
radiation from the source provides a relatively high level of
illumination. However, some light from the source impacts on the
diffusely reflective surfaces of the mask and cavity. The
constructive occlusion of the invention provides lower intensity
illumination in the angular range, from where the direct
illumination ends, up to and including the system axis (vertical in
FIG. 4). Recall that in the runway light example, the specification
requires an average illumination of 2 candela from the horizon to
at least 6.degree. above the horizon. For angles from 6.degree. up
to the system axis (vertical), the specification requires an
average illumination of 0.2 candela. The field of illumination
around the runway light extends through 360.degree..
[0057] FIG. 4 provides an isometric view of the system 31, whereas
FIG. 5 provides an exploded view showing the cavity 33, the mask 35
and the LED light sources 37. Again, the inner surface of the
cavity has a substantial diffuse reflective characteristic. At
least the surface of the mask facing toward the LEDs 37 and the
aperture 39 of the cavity 33 is diffusely reflective. A flat
reflective shoulder 41 surrounds the aperture 39 of the cavity. The
reflective characteristic of the shoulder 41 preferably provides
highly efficient diffusion.
[0058] As shown in these drawings, the source used in the system 31
comprises a ring of outwardly facing LEDs 37. The LEDs emit visible
light, such as blue light. The mask 35 is positioned outside the
cavity 33 at a distance from the aperture 39. The spacing between
the lower surface of the mask 35 and the aperture 39 is sufficient
for placement of the LEDs 37 in the space between the mask and
aperture. As a result, the LEDs have a direct view with respect to
a substantial range of elevation angles covering a portion of the
area to be illuminated (vertical elevation in the drawings). The
gap between the mask 35 and the shoulder 41 defines the effective
aperture, limiting the elevational angles directly illuminated by
the LEDs 37. The ring of LEDs provides substantially continuous
illumination outward around the system 31 (around the horizon in
the illustrated orientation). Each LED 37 is oriented to emit light
along and about a radius out from the system axis.
[0059] Commercially available LEDs of sufficient output power for
application to airport lighting typically have either a 15.degree.
or 30.degree. nominal field of view. A typical example of one of
the LEDs used in the illustrated embodiment might emit direct
illumination over approximately a 30.degree. field of view centered
about the emission axis. The LED emits 30-40% of its light within
this nominal field of view. A ring of 12 radially emitting LEDs 37
provides substantially complete coverage outward around the horizon
of the system 31.
[0060] In a practical structure built as shown, the LEDs 37
actually are attached to the mask 35. The mask 35 has an opening or
tube 43 (FIG. 4) extending away from the cavity 33, for passage of
wires (not shown) used to supply electric drive power to the leads
45 (FIG. 5) of the LEDs 37.
[0061] As noted, each of the LEDs 37 emits 30-40% of its light
within its nominal field of view. Assuming the vertical orientation
shown, for angles in the horizontal direction, the light from the
LEDs combines to provide the desired full-circle direct
illumination. In the vertical direction, most of the light emitted
in the nominal field of view passes between the mask 35 and the
shoulder 41, to provide the desired high-intensity direct
illumination at low elevation angles (near the horizon). The mask
and shoulder may limit the LED aperture to further limit the field
view somewhat with respect to elevation angle. Also, some of this
light directly emitted from the LEDs 37 will diffuse and reflect
upward from the surface of the shoulder 41. In this manner, the
highest intensity is provided in the elevational region extending
up from the horizon, and the intensity from the direct illumination
begins to drop off somewhat at the upper edge of the field of view
as defined by either the nominal field of view of the LEDs or the
limiting aperture formed by the mask and the shoulder.
[0062] Each of the LEDs 37 also emits some light at angles outside
the nominal field of view of the LED, that is to say further from
the LED axis. The mask and cavity system captures much of this
additional light, for constructive occlusion type processing and
illumination. Specifically, the mask 43 constructively occludes a
substantial portion of the aperture 39 of the cavity 33,
particularly with respect to high elevational angles going up to
and including those at and about the system axis (vertical in FIG.
4). Light captured between the diffuse surfaces of the mask 35 and
the cavity 33 reflects and diffuses repeatedly until it emerges
from the gap between the outer edge of the mask 43 and the
perimeter of the aperture 39. The occlusion by the mask 35 is
constructive in that it provides a desirable distribution of light
over at least a portion of the intended angular range of
illumination by the system 31. In this case, the dimensions and
positioning of the mask 35 relative to the aperture 39 are
specifically chosen to meet the requirements for illumination at
the higher elevation angles, as established for airport lighting
systems.
[0063] A runway lighting system constructed in accord with the
invention could theoretically use a minimum of six LEDs. Preferred
embodiments use 10-12 LEDs. The examples shown in FIGS. 4-6 utilize
12 LEDs, for example, where each of which has a 30.degree. field of
direct illumination. Alternatively, the system 31 could utilize
LEDs with a 15.degree. nominal field of view. However, such a
system would then use a series of lenses (not shown) having an
astigmatism to spread the light from each LED horizontally but
maintain the 15.degree. vertical spread of light emissions from
each LED. Any such system, constructed with 15 or fewer LEDs,
clearly uses far fewer LEDs than prior attempts to construct
airport lighting systems with LEDs. As such, the cost and power
requirements are much lower. Also, the simplified structure tends
to make the system particularly rugged and durable.
[0064] FIGS. 6-8 depict a preferred embodiment of an inventive
lighting system 51 for taxiway or runway lighting. FIG. 6 is an
isometric view of the lighting system 51, and FIG. 7 is a top plan
view of the system 51. FIG. 8 is a detail view of a lens ring 53
mounted on the shoulder 41.
[0065] The system 51 is generally similar to that of FIGS. 4 and 5
in that includes a cavity 33, a mask 35 and a ring of 12 radially
directed LEDs 37 located between the aperture 39 and the mask 35.
In this embodiment, however, each of the LEDs 37 has a nominal
field of illumination of 15.degree.. The nominal 15.degree. field
of illumination includes approximately 30-40% of the light from the
LEDs and provides adequate intensity for the direct view
illumination at low angles of elevation, as required for the
airport application.
[0066] However, the direct radiations from 12 LEDs with this field
of illumination would not cover a full circle (360.degree. in the
horizontal direction) around the lighting fixture 51. Accordingly,
the system 51 includes a lens ring 53 made of a clear acrylic. The
ring 53 is mounted on the shoulder 41 and extends vertically from
the shoulder. The ring 53 is the same height as or slightly higher
than the lower edge of the mask 35. The ring 53 is dimensioned so
that the inner surface thereof is located at a short distance
radially outward from the aperture 39, and thus from the LEDs. The
inner surface of the ring forms a smooth, cylindrical surface.
[0067] Various segments of the outer surface of the acrylic ring
are contoured. Specifically, each segment 55 of the ring 53 that is
in front of one of the LEDs covers at least the 15.degree. field of
illumination of the respective LED. The outer surface of each such
segment 55 has a horizontal concave contour, so that the segment 55
acts as a lens to disperse the light emitted with the 15.degree.
angular range (horizontal) outward to cover approximately a
30.degree. field of illumination. The lens sections 55 do not cause
any substantial vertical refraction.
[0068] The segments 57 between the lens 55 have a smooth outer
surface corresponding to sections of a cylinder. The sections 57
are transparent and pass light, albeit with limited horizontal
dispersion. With the lens ring 53, the 12 LEDs 37 can produce a
ring of high intensity light for direct illumination up to an
elevation of 15.degree. above the horizon but covering a full
360.degree. circle in the horizontal direction.
[0069] Again, the LEDs 37 emit a substantial portion of light in
directions outside the 15.degree. nominal field of view. The mask
35 and the cavity 33 reflect and diffuse much of this light, and
the constructive occlusion of the aperture 39 by the mask 35
produces a substantially omni-directional distribution, with
appropriate intensity at elevation angles above the 15.degree.
field directly illuminated by the LEDs 37 through the lenses
55.
[0070] FIG. 9 shows an approximation of the intensity distribution
with respect to angle from the axis, for the system 51 of FIGS.
6-8. The system axis represents a 0.degree. angle (vertical),
whereas the horizon regions correspond to 90.degree. and
-90.degree.. Low elevation angles, near the horizon, would have
angles relative to the axis approaching .+-.90.degree..
[0071] As shown, the system 51 provides relatively high intensity
distribution over the regions approaching .+-.90.degree.,
specifically, for approximately 15.degree. above each horizon. This
high intensity illumination, from the direct irradiation from the
LEDs, provides 2 candela or higher illumination throughout the
regions from each horizon (90.degree. or -90.degree.) up to and
somewhat beyond the 6.degree. boundary (.+-.84.degree.) specified
in the requirements for airport lighting. As the elevation angle
passes from the region of direct illumination, the magnitude of the
angle with respect to the axis falls, and the direct illumination
from the LEDs falls off substantially. The illumination would go to
zero nearer the axis, but with the invention, such regions are
illuminated by the constructive occlusion mask-and-cavity system.
As the angle approaches the axis, the total illumination drops, but
only to an average level at or slightly above 0.2 candela, fully
satisfying the requirements for illumination in the region over the
light fixture, set for airport lighting applications. Those skilled
in the art will recognize that the lighting system 51 will have a
variety of other applications.
[0072] FIG. 10 illustrates another embodiment of the invention. The
lighting system 61 of FIG. 10 is generally similar to the system 11
of FIG. 1, with the principal difference being that the source 63
directly illuminates a region about the system axis through an
aperture 65 through the mask 67.
[0073] In this embodiment, the radiant energy distributor includes
a base 69 with a cavity 71 formed in the side thereof facing toward
the intended field or area to be illuminated. A variety of cavity
shapes could be used, depending on the particular lighting
application that the system will serve. In the illustrated example,
the cavity comprises a segment of a sphere and may be
hemispherical.
[0074] The rim or edge of the cavity 71 forms an aperture 73. The
base 69 includes a flat, ring-shaped shoulder 75 surrounding the
aperture 73 of the cavity 71. A disk-shaped mask 67, disposed
between the base 69 and the area to be illuminated, occludes a
substantial of the aperture 73 of the cavity 71 with respect to
that area. At least a portion of the surface of the cavity 71 and
the surface(s) of the mask 67 facing the cavity 71 are highly,
diffusely reflective. In the preferred embodiment, the entire
cavity surface and the shoulder 75 are diffusely reflective.
[0075] In this embodiment, the radiant energy emitter 63 is a light
bulb illuminated by electrical energy supplied from a ballast or
the like (not shown). The mask 67 incorporates a reflector 77
surrounding the light bulb 63, to efficiently project much of the
radiant energy from the bulb 125 into the diffusely reflective
cavity 71. The inner surface of the reflector 127 may have a
specular reflective characteristic but preferably is diffusely
reflective.
[0076] For an application requiring a high intensity illumination
at a region nearer the axis of the system, the mask 67 includes an
aperture 65 extending from the reflector 77 through to the opposite
surface of the mask 67. The additional aperture 65 enables direct
illumination of a predetermined portion of the region specified for
illumination by the system 61. In the illustrated example, the
aperture 65 is formed above the system axis and enables direct
illumination of an area around the axis limited in angle by the
size of the aperture, for example between the ray lines L5. The
position and size of the aperture are designed to satisfy the
requirements of a particular application. For example, for another
application, the aperture 65 might be larger or smaller or it might
be oriented to emit direct radiation in a region somewhat separate
from the central axis.
[0077] FIGS. 11 and 12 depict still further embodiments of the
invention, similar to the embodiment of FIG. 1, but utilizing a
baffle or the like within the cavity to serve as a "kicker"to
direct additional light out into the regions near the horizon. As
in FIG. 1, each of these systems includes a base 13 with a
diffusely reflective cavity 15 and a mask 19 positioned to
constructively occlude the aperture 23 of the cavity 15. A
shoulder, preferably with a reflective surface, surrounds the
aperture 23. A source 21 is located in the region between the mask
and the cavity so as to directly illuminate certain regions and to
direct addition radiation into the cavity 15. In the illustrated
examples, the source 21 is mounted beneath and adjacent to the
diffusely reflective surface of the mask 19 that faces toward the
aperture 23. Each of these embodiments also includes a diffusely
reflective element within the cavity, to "kick" additional light
from the cavity out toward regions low down near the horizon around
the respective system.
[0078] The illumination system 71 of FIG. 11 includes a baffle 123
disposed in the cavity 15. The baffle 123 has a flat, circular,
planar surface 123.sub.1 formed about the axis of the mask 23 and
the cavity 15. The baffle or kicker 123 preferably has a shape
corresponding to the shape of the cavity and its aperture.
[0079] The planar surface 123, is substantially parallel to the
cavity aperture 23. As 20 illustrated, the surface 123.sub.1 is
disposed within the cavity 15 at a distance from the aperture
(below the aperture in the illustrated orientation). However, the
surface 123, could be in the plane of the aperture or on a plane
between the aperture and the mask, depending on the distribution
characteristic desired. The edges of the circular baffle are
beveled to form a ring-like annular surface 123.sub.2 at an angle
with respect to the planar central surface 123.sub.1. The baffle
123 may substantially fill the inner portion of the cavity, as
shown, or the baffle 123 may comprise a beveled disk or plate
extending across the cavity 15. The baffle is located within the
cavity and beveled in such a manner as to leave a segment of the
cavity surface around the aperture exposed to light. At least this
segment of the cavity 115 and the exposed surfaces of the baffle
123 are highly, diffusely reflective. The baffle 123 serves to
reflect more of the light from the lamp 21 out to the periphery of
the desired illumination footprint, further increasing the
intensity provided in those regions.
[0080] When viewed from the area illuminated, the source 21 appears
brightest, and next the planar surface 123.sub.1 appears brightest.
Some light reflected from points on the planar surface 123.sub.1 is
directed towards regions relatively far-off the axis of the system
at low elevational angles only slightly above the horizon. There
will be some overlap with the direct illumination from the source
21. The angled annular surface 123.sub.2 of the baffle 123 will
appear to the observer to be slightly dimmer than the surface
123.sub.1. The light from this surface will fill in an area of the
footprint somewhat above and closer to the axis than that
illuminated by the planar surface 123.sub.1, and the intensity will
tend to decrease as the angle approaches the system axis (higher
elevational angles). The segment of the cavity 15 exposed around
the edge of the baffle plate 123 also diffusely reflects some light
into the area of intended illumination. However, because of the
angle of this segment, when viewed from the area illuminated the
segment appears dimmer than either the surface 123.sub.1 or the
surface 123.sub.2. The light from this surface will fill in an area
of the footprint in regions closer to the axis than those
illuminated by light reflected from surfaces of the baffle 123, and
this light will tend to decrease further in intensity as the angle
of emission approaches the axis. Each of the diffusely reflective
surfaces of the baffle 123 and the diffusely reflective exposed
segment of the cavity 15 will also reflect some light back for
further reflection and diffusion between the mask, the cavity and
the baffle.
[0081] The diffusely reflective shoulder 17 also will direct at
least some of the light into the field of intended illumination.
The intensity distribution of light reflected from the shoulder
when measured at a distance from the device tends to form a bell
shaped curve, centered about the axis of the device (vertical in
FIG. 7). However, because of the geometry of the system, the
intensity of the light reflected from the shoulder is much smaller
than that provided by direct radiation from the source or that
emitted from reflection from the cavity and the baffle
surfaces.
[0082] Each point on the device components that is diffusely
reflective will reflect light in many different directions. The
mask, cavity, baffle and reflector will reflect and diffuse each
beam of light from the source many times before emission from the
system. However, because of the highly reflective nature of the
material surfaces, the device remains extremely efficient, with
relatively little light absorbed within the system. The careful
tailoring of the intensity distribution in fact maximizes the
amount of emitted light kept within useful portions of the
illuminated footprint and optimizes the distribution thereof, to
maximize illumination efficiency within that area for a particular
lighting application.
[0083] In the example shown, the baffle 123 is symmetrical about
the system axis. In some embodiments, it may be desirable to vary
the contour of the baffle on different sides of the device. For
example, on one pair of sides, the bevels might appear essentially
as shown in FIG. 11, whereas when viewed in cross-section at a
right angle to the illustrated view, the bevel of the annular
surface might cut more deeply, either at a different angle or
further back toward the axis of the baffle. In the illustrated
example, the planar surface 123.sub.1 is circular. In a version
having a modified bevel to the annular surface, the planar surface
123.sub.1 might become oval or elliptical.
[0084] FIG. 12 discloses an alternate embodiment, similar to the
embodiment of FIG. 11 but having a different baffle structure. In
this embodiment, the baffle 133 is disposed entirely within the
cavity 15. The baffle 133 comprises an assembly of plates forming
reflective walls at right angles to each other, projected upward
from the inner wall of the cavity 15 toward the aperture 23 and the
underside of the mask 19. The baffle plates divide the cavity into
quadrants. Although shown as four walls extending at right angles
to one another, those skilled in the art will recognize that the
baffle may comprise fewer radially extending walls or more radially
extending walls, e.g. three walls at 120.degree. angles or five
walls at 72.degree. angles. In other embodiments not shown, but
similar to FIG. 12, the baffle structure may be formed on the
surface of the mask facing toward the aperture.
[0085] The embodiments discussed in detail above can meet the
illumination requirements of many applications. Examples discussed
included lighting fixtures intended to provide uniform planar
illumination over a wide area and specialized lighting systems for
airport taxiways or runways. However, the principles of the
invention also support many other applications. Another example of
an application of the invention relates to emergency lighting
systems, to enable personnel to exit a facility in the event of a
failure of the regular lighting system. Typically, the light
fixture is ceiling or wall mounted. The emergency light must
project a large quantity of light laterally and provide some light
in regions closer to the system axis. Again, the combination of
direct lighting and constructive occlusion provides a highly
efficient solution to the distribution requirements of this type of
lighting application. Using fixtures constructed in accord with the
invention, it is possible to illuminate a long exit path with a
consistently uniform intensity, for example at 1 foot-candle,
without any excessive fluctuations in intensity along the path and
with fewer light fixtures. The concepts of the invention also find
application in emergency enunciator systems, i.e. the flashing
strobe lights used to alert personnel of the emergency need for
evacuation of the facility.
[0086] While the foregoing has described what are considered to be
preferred embodiments of the invention it is understood that
various modifications may be made therein and that the invention
may be implemented in various forms and embodiments, and that it
may be applied in numerous applications, only some of which have
been described herein. It is intended by the following claims to
claim all such modifications and variations which fall within the
true scope of the invention.
* * * * *