ILLUMINATION SYSTEM INCLUDING A VIRTUAL LIGHT SOURCE
REPLY TO
ATTN OF: GP
MEMORANDUM
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C'. 20546
July 6, 1971
FROM :
~~~/Scientific & Technical Information Division _ Attn: ~iss Winnie M. Morgan
~~/~ffice of Assistant General
Counsel for Patent Matters
SUBJECT: Announcement of NASA-Owned
U.S. Patents in STAR
In accordance with the procedures contained in the Code GP
to Code US1 memorandum on this subject, dated June 8, 1970,
the attached NASA-owned U.S. patent is being forwarded for
abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No.
Corporate Source
Supplementary
Corporate Source
: Bausch & Lomb, Inc.
NASA Patent case No.: MQ?- /dYf/
wL Gayle Parker
Enclosure :
Copy of Patent
https://ntrs.nasa.gov/search.jsp?R=19710020816 2018-08-31T18:58:18+00:00Z
March 8, 1966 J. F. HALL, JR 3,2391,660
Filed Jan. 31, 1961 2 Sheets-Sheel I
FIG. I
INVENTOR.
JOSEPH E HPbLk JR.
ATTORNEYS
March 8, 1966 J. F. HALL, JR 3,239,668
ILLUMINATION SYSTEM INCLUDING A VIRTUAL LIGHT SOURCE
Filed Jan. 31. 1961 2 Sheets-Sheet 2
FIG. 2
FIG. 3
FIG. 4
INVENTOR.
JOSEPI-I E HALL JR.
3,239,668 United States Patent Office ,a,,,,, ,,,* , ,,,,
2
Briefly, an illumination system according lo the present
3,239,660 invention comprises an array of real light sources, means ~~&~M~NAT~ON SYSmM m(1.LUDmG A VIRTUAL for directing light from all of the sources into a common, LIGHT SOURCE relatively confined path toward a multi-fac-tcd reflector, "~~~6)~~2~~'L$9$~~~2~$i2k~lgf~~~~~,"et~,"2$~ 5 which will be described in greater detail hercinaftcr and
slows of 42 U.S.C. 2457Cd) which serves as a virtual source. The reflector distributes
Piled Jan. 31, 1961, Ser. No. 86,018 the light received from the real sources over a reiatibeiy
8 Claims. ((1.1.240-41.36) wide angle, and directs it toward a collimating reflector
thereby illuminating the desired field. The intensity of
hi^ invention relates to a novel illumination system 10 illumin~ation from the virtual source constituted by the
including plural, spaced light sources and means for corn- multi-faceted reflector is directly proportional to the
bining their outputs to form a single virtual source. number of real sources that are ei?ergizei! at any given
Illunlinalion systems of the type in which it is desired time. Because of the nature of the multi-f~cetcd reflector
to vary the intensity of illumination without varying its and the manner in which it distribute$ light ~rn~in~ii?~
color, or the spectral distribution of the energy content 15 upon it, the field is always relatively un~forrnly rlltimihave
heretofore depended largely upon variable stops or naied regardless of which ones of the real sources are neutr~l density optical wedges for controlling the intensity energized or de-energi~d.
of the illumination. These systems necessarily involves The present invention was developed in connection with
a loss of eacency as the illumination is attenuated, and a gun simulator system for use with an oiater space cnare
not economically useful in systems capable of produc- 20 vironmental test chamber, and is believt-cl to be espeing
reiaiilreiy high intensity illulnination such as, for ex- cially advantageous for such application It is also example,
sun simulator systems. pected, however, thtat the invention v~lill find advanIn
a sun system, it is desirable to provide tageous application in other cases wheie s,mriar diesigci
means for varying the intensity of illumination over a requirements are to be considered.
relatively wide range without change in the spectral dis- 25 Referring now to the drawings, an ill~~minetion system
tribution of the illumination, so that the simulator may according to a presently preferred embodimrni of rhe inbe
used to simulate not only sunlight, but also earthlight vention is illustrated in FIG. 1 arranged as a sun slmrrand
moonlight. In order to provide sufficient illumination lator for illuminating the interior of an outer space ento
simulate sunlight over a practicably large area, it is vironmental test chamber 10, in whrch an object such as
necessary to employ plural light sources, and it is desirable 30 a space satellite may be placed for lest purposes. The
to control the intensity of illumination by varying the illumination system of the invention incl~~dcs an array
number of the light sources that are energized, thereby 12 of real light sources 14, which are preferzbly xenon
avoiding changes in the spectral distribution of the light or mercury-xenon high pressure arc lamps, because thc
output of the simulator, and maintaining a relatively high light output of such lamps relati~c'y closely app~oxidegree
of eficiency. It is also desirable to avoid localized mates sunlight with respect to its spectral d~qlribution.
field darkening effects caused by the selective extinguish- Any desired means (no1 shown) arc provtded for sclecrnent
of the individual light sources, and to maintain uni- tively energizing different ones of the lamps 14. $he
formity of illumination over the entire field toward which lamps 14 are arranged in a disc-like may, and individ~iai
the illuminator is directed. parabolic reflectors 16 are positioned behlncl the respecAccordingly,
one important object of the present inven- 40 tive lamps 24 for directing light from the lamps gcntion
is to provide a novel illumination system including erally downwardly toward a single, upwardly concave
means for combining the outputs of plural light sources parabolic reflector 18. The lamps 14, and the reflectors
to form a single virtual source, the intensity of which varies 16 are mounted on a framework gcneraliy design,~+cd
in accoidance with the number of individual real sources 20, which is supported on a plurality of I-beams 22. Pn
that are selectively energized at any one time. 45 those cases where relatively large pourer outputs are re- Other objects are: to provide a novel illumination sys- quired, as in the present sun simulator, the I-beams 22
ten1 particularly suitable for use as a sun simulator in are preferably cooled by a liquid circuIateir ~hiough
conjunction with an environmental test chamber; to pro- pipes 24 arranged in thermal contact with the I-isednls 22
vide a novel illumination system of this type in which The concave reflector 18 converges the 11g11i lrocl the
the real light sources may be positioned exteriorly of the 50 individual light sources 14, and directs it roiv~id a ieldtest
chamber and their light outputs directed into the test tively small diameter, convex, hype1 bolii mirror 26,
chamber through n relatively small window; to provide a which is located at the center of the array 12, facing dw~nnovel
il!u:nination system of this type including means wardiy. The relative curvatures of the concave refleefor
producing a virtual source within the chamber, the tor 18 and the convex mirror 26 are chosen so that the
intensity of which is proportional to the total number of 55 light coming downwardly from the convex ~llirror 26 is
the real sources that are energized at any given time; substantially collimated.
and in general, to provide an illumination system of this A window 28 in the form of a lens is mounted in the
type which is of relatively simple and rugged conslruc- cover 130, of the chamdber 10, and the collimated light
tion, and reliable and convenient in operation. from the convex mirror %6 passes through the window
The foregoing and other objects and advantages of the 60 28. The optical power of the window 28 is selectcd to
invention will become apparent in the following de- image the convex rdector mirror 26 upon the multitailed
description of a representative embodiment there- faceted reflector 30, which is fixed vvithin the chamber
of, taken in conjunction with the drawings, wherein 180 directly beneath the windolw 28 and optically aligned
FIG. 1 is a partly schematic, vertical sectional view with the window 28 and the canvex reflector 26, Thus,
of a sun simulator according to the present invention; 65 the array 12 is imaged on the multi-faceted reflector 30,
FIG. 2 is a partly schematic, verticel sectional view which becomes a virtual light source wiihin the lest cham- on an enlarged scale of the array of light sources in- ber 10.
cluded in the sun simulator shown in FIG. 1; The parabolic reflector receives a collimated light from
FIG. 3 is a iragrnentarp bottom view of the array of the plurality of light sources 14 and refledors $6 asso- light sources, and 70 ciated with said sources. The hyperbolic reflector 26
FIG. 4 is an enlarged cross section view of the plu- bares a relationship to the paraioolic reflector IS such that
naiity of hyperboloids of revolution. when the virtual focus of the hyperbolic reflector and the
3,239,660
3 4
focal point of the parabolic reflector are coincidental, ria1 for these reflectors, and reIativeIy large, accurately
the light reliected from the hyperbolic reflector 26 is sub- curved glass or metal surfaces such as those exceeding
stantially collimated. This relationship is a character- about ten feet in diameter are not readily available. These
istic of these two types of refleotors in the combination as and other variations in datails of construction will be
illustrated, It is of course necessary that the proper 5 well within the skill of those familiar with the art.
reflectors t?e selected to provide a collimabion as indi- What is claimed is:
cated. 1. A light source for use in conjunction with an cn- Thc light reflected from the [hyperbolic reflector 26 is vironment test chamber comprising an array of real
however slightly convergent as it is reflected from the light soulces, means defining a test chamber, said array
reflector, This 1s due to the fact that the parabolic focal 10 disposed outside of the chamber, a light converging repoint
is iniermediate the parabolic reflector 18 and the flector intermediate said chambcr and said alray, reliiit~~al
focal point of the hyperbolic reflector 26. The flectors individually associated with each one of said real
distance beiwcen the two focal points controls the con- light sources directing light in a comnlon direction toward
vergence of the iays ieflected from the hyperbolic reflector the chamber and said reflector, a divelgent reflector posi26,
It lb necesaary however that the central axis of both 15 tioned adjacent to said array receiving light from said con- tne rcflectars 18 and 26 be coincidental. vergent reflector and directing collimat~ng light so received
Thc multi-faceted reflector 30 is a highly reflective sur- towald the chamber, a reflector composed of a close
face p~eferably in the form of a close packed array of packed array of curved surfaces positioned within the convex bypeiboloids of revolution. It distributes the chamber facing said divergent reflector forming a plurality light received by it, causing the light to diverge upwardly 20 of virtual light sources within the chamber, a lens conioward
a downwardly directly parabolic reflector 32. The stituting a window in the chamber wall imaging said
rntiltl-faceted reflector 38 serves to "scramble" the image divergent surfaces of said reflector upon said close paclced
of the array 12. Each hype~bolic portion of the reflector reflector, a second light converging reflector mounted
30 riiumina~tes substantially the entire surface of the down- wrthin said chamber receiving light from said close
wdrd!y fac~ng parabolic reflector 32, so that even in the 25 packed surfaces on said reflector and collimating light
event that only one randomly selected light source 14 so received within the test chamber.
1s energized, and only a rela~tively small portion of the 2. An illumination system for use in conjunction with
multi-facetc;ci reflector is illuminated, the entire surface an environmental testing chamber comprising an array
oi the downwardly facing reflector 32 will be relatively of real light sources, means defining a test chamber,
uniformly illuminated. 30 said array disposed outside of the chamber, reflectors
The reflectors 30 and 34 are axially coincidental with individually associated with each one of said real light
the para~oilc reflector 32 and the hyperbolic reflector 26. sources directing light in a comrnon direction toward
Each of the reflectors 30 and 34 are formed by a reflect- the chamber, a concave parabolic reflector mounted admg
piuraiity surface 40 simulating hyperboloids of revo- jacent to said chamber facing said may, a convex hyperlwtion
havrng a characteristic of reflecting light with a 35 bolic retlector centrally mounted adjacent to said array
lrniform illumination over the surface of the parabolic facing said parabolic reflector, the curvatures of said
reflector 32 and 36 respectively. The surfaces form a parabolic and hyperbolic reflectors being selected to provirtual
source 41 as indicated. The hyperbolic surfaoes duce a substantially collimated beam of light from said
of refiector 34 ho~~ever reflect against the hype~bolic re- hyperbolic reflector, a multi-faceted refl~ctor composed
fiector 36. 40 of a close-packed array of convex hyperboloidal surIn
relatively large systems such as the system for which faces positioned within the chamber facing said hyperthe
herein. described embodiment of the invention was de- bolic reflector, lens means in the wall of the chamber
veloped, st may be desirable to provide an auxiliary multi- imaging said hyperbolic reflector upon said close-packed
faceted reflector 34, and a corresponding parabolic reflec- array reflector, each one of said hyperboloidal surfaces
tor 36 to fill in the shadow cast by the first multi-faceted 45 being no larger than the size of an image formed thereat
reflector 30. For example, when the main downwardly of one of said real light sources by said parabolic reiac1n.g
parabolic reflector 32 is about twenty-five feet in flector, said hyperbolic reflector, and said lens means,
diameter, the main multi-faceted reflector 30 may be and a second hyperbolic reflector mounted within the
about thirty inches in diameter, and thus cast an appre- chamber collecting and collimating light reflected from
ciable shadow within the chamber. In order to minimize 50 said close-packed array reflector.
the shadow, the main multi-faceted reflector 30 may have 3. An illuminating system comprising a plllrality of
a control aperture 38 permitting a relatively small por- light sources including means radiating a substantially
tion of the light to pass through the main multi-faceted collimated luminous flux, a multi-faceted reflector inraflector
30 and fall upon an auxiliary, relatively small cluding a plurality of surfaces of revolution constructed
dan~eter andti-faceted refleotor 34. The auxiliary reflec- 55 and arranged with their axes of rotation in parallel retor
34 then directs the light received by it upwardly to lationship relative to each other, reflector means receiv-
;n auxi11ary parabolic refiector 36 in an exactly similar ing the luminous flux from said plurality of light sources manner as the nuin multi-faceted reflector 30. and directing the luminous flux on said multi-iaceted
The rnrrlti-faceted reflectors 30 and 34 may take any reflector, light directing means receiving uniform light
desired lorm. Preferably, for maximum efficiency their 60 from said multi-faceted reflector in response to lhe illuworklng
surfaces are highly reflective over the entire mination of any of said facets in said multi-faceted respectral
range of the illuminating system, so that they flector and directing uniform illumination over a prewill
absorb a minimum proportion of the energy imping- determined area.
Ing ilpon them. They may be relatively finely textured, 4. A sun simulator comprising an array of light sources
provided they achieve adequate scattering of the col- 63 radiating collimated light each having a light output
llrnated light impinging upon them, or they may be, for simlating the spectral outpat of sunlight, a reflector
example, of a relatively coarse, nodular texture as in the comprising a close packed array of hyperbolic reflecthjperboloidal
array described hereinabove. Each nodule, ing surfaces having axes in parallel relationship, sald
or curved facet is preferably no larger than the size the icflector constructed and arranged in a manner forming
image oi a single one of the real light sources 14 formed 70 a plurality of virtual light sources providing illuminaon
the reflector. tion of an intensity proporti~nal to the number of light
In relatively large devices of this character, the para- sources energizing and with a special distribution which
bolic reflectors 118 and 32 are preferably made in sec- remains substantially constant despite vnliaticris of its
tional form lor convenience in manufacture and assem- intensity due to cha~lges in the number of said light
bly. Generally, glass or metal is a preferred base mate- 7.5 sources that are energized, a light converging optical sys-
3,239,660
5 6
tem directing light from said plurality of sources to an intensity proportional to the number of light sourccs
said reflector, a collimator receiving light from said re- energized.
flector and directing collimated light over a predetermined 8. An illuminating system comprising an array of area. real light sources, a parabolic light reflector associated
5. An illuminating system comprising a plurality of 5 with each of said light sources reflecting a substantiatljr
light sources radiating a substantially collimated lumi- collimated luminous flux, a multi-faceted reflector in- nous flux, a reflector defining at least a portion of a cluding a plurality of facets defining at least a portion
surface of a hyperboloid of revolution, any portions of a paraboloid of revolution having parallel axes with
of surfaces of revolution having axes arranged in paral- each of said facets forming a virtual source no larger
lel relationship, an optical system intermediate said plu- than the size of said sources, an optical system includrality
of light sources and said reflector constructed and ing parabolic reflectors imaging said array of light sources
arranged for increasing the intensity of the luminous on said multi-faceted reflector, a parabolic collimator
flux directed on said reflector, light gathering means re- receiving uniform illumination from each of said pluceiving
light from said reflector and projecting a luminous rality of facets of said reflector and reflecting a subflux
of decreased intensity in a substantially collimated 15 stantially collimated luminous flux of the intensity pro- manner. portional to the number of light sources energized.
6. An illuminating system comprising a plurality of
light sources radiating a substantially collimated flux, a References Cited by the Examher
multi-faceted reflector, said facets defining hyperboloids
of revolution having parallel axes and forming virtual
image sources reflecting light equally in all directions
about an axis of the hyperboloid of revolution, an optical
system intermediate said sources and said facets
receiving the luminous flux from said sources and focusing
the luminous flux on said facets, a collimator receiving
light from said facets of said multi-faceted reflector
and projecting a uniform illumination.
7. An illuminator system comprising an array of real
light sources aligned in parallel relationship and radiating
a substantially collimated luminous flux, a multifaceted
reflector incuding a plurality of surfaces of revolution
axially in parallel alignment relative to each other,
an optical system intermediate said sources and said
facets imaging said array of light sources upon said
facets, a parabolic collimator means receiving light from
said plurality of facets constructed and arranged to project
uniformity of illumination from said collimator of
UNITED STATES PATENTS
5/1918 McKeever -------- 240-41.36
1/1935 Wahlberg -------- 240-41.6 X
11/1941 Gensburg --------- 240-41.35
6/1942 Wahlberg -------- 240-41.6 X
6/1955 Jorn --------------240-47 X
5/ 1956 Ferguson --------- 240-46.49
7/1956 Ott et al. -------- 240-41.1 X
4/1957 Rosin ------------- 240-41.1
FOREIGN PATENTS
128,240 6/1919 Great Britain.
832,378 4/1960 Great Britaiin.
NORTON ANSHER, Primary Exanzi~zer.
GEORGE A. NINAS, JR., EMIL, G. ANDERSON,
SAMUEL FEINBERG, Examiners.
