U.S. patent number RE33,471 [Application Number 07/472,172] was granted by the patent office on 1990-12-04 for method for indirect lighting.
This patent grant is currently assigned to Peerless Lighting Corporation. Invention is credited to Douglas J. Herst, Peter Y. Y. Ngai.
United States Patent |
RE33,471 |
Herst , et al. |
December 4, 1990 |
Method for indirect lighting
Abstract
A method for indirectly illuminating an interior space is
disclosed wherein a laterally extended overhead distribution of
light is produced from a source of indirect lighting, such as a
fluorescent indirect luminaire, by directing a portion of the
source light upward to produce a luminance pattern on the ceiling
surface directly overhead and then refracting substantially all of
another portion of the source light laterally of the indirect
luminaire so as to spread the refracted portion away from the
directly overhead luminance pattern. Illustrated is a luminaire
having trough-shaped lensed for achieving the method of the
invention wherein the lateral portions of the lens act to refract
the light laterally as above described, and the top lens portion is
formed to diverge the light incidence thereon directly overhead in
a substantially uniform luminance pattern which is extended by the
light refracted through the lateral lens portions.
Inventors: |
Herst; Douglas J. (Ross,
CA), Ngai; Peter Y. Y. (Lafayette, CA) |
Assignee: |
Peerless Lighting Corporation
(Berkeley, CA)
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Family
ID: |
27489115 |
Appl.
No.: |
07/472,172 |
Filed: |
January 30, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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742591 |
Jun 7, 1985 |
4667275 |
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46970 |
Jun 8, 1979 |
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Reissue of: |
840099 |
Mar 17, 1986 |
04660131 |
Apr 21, 1987 |
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Current U.S.
Class: |
362/223; 362/337;
362/309 |
Current CPC
Class: |
F21V
5/02 (20130101); F21V 7/0008 (20130101); F21S
2/00 (20130101); F21S 8/088 (20130101); F21S
6/005 (20130101); F21Y 2103/00 (20130101); F21W
2131/402 (20130101) |
Current International
Class: |
F21V
7/00 (20060101); F21V 5/00 (20060101); F21V
5/02 (20060101); F21S 003/00 () |
Field of
Search: |
;362/217,219,223,260,307,308,309,311,327,328,329,330,332,335,336,337,339,340,367 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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619084 |
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Mar 1949 |
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GB |
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924138 |
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Apr 1963 |
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GB |
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Other References
Peerless Electric Company, Photometric and Technical Information,
Longlites by Peerless, 1977, pp. 82-95. .
Electro-Systems, Inc., Power-Lume 800/1500, 1965, p. 5. .
Holophane Company, Inc., Outdoor Substation Unit with Lens Top,
D4252, 1966..
|
Primary Examiner: Okonsky; David A.
Attorney, Agent or Firm: Beeson; Donald L.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a division of pending application Ser. No.
742,591, filed June 7, 1985, .Iadd.now U.S. Pat. No. 4,667,275
.Iaddend.which is a continuation of application Ser. No. 046,970
filed June 8, 1979, now abandoned.
Claims
What we claim is:
1. A method of indirectly illuminating an interior space having a
ceiling surface comprising the steps of
(1) positioning a source of indirect light at a distance below said
ceiling surface,
(2) directing a portion of light from said source of indirect light
upward to produce a luminance pattern on said ceiling surface
directly overhead said source of indirect light, and
(3) refracting substantially all of another portion of said source
of indirect light laterally of said indirect light source so as to
spread same away from said directly overhead luminance pattern to
provide a laterally extended overhead distribution of light.Iadd.,
and so that some of said lateral spread of light is directed into
viewing angles below the indirect source of light whereby the
source of indirect light can be perceived by persons located below
and to the side of said source of indirect light.Iaddend..
2. The method of claim 1 wherein the source of indirect light is
comprised of at least one elongated luminaire having a light
source, an elongated opaque housing extending upwardly about said
light source, and a lens means mounted above the housing having a
lateral prismatic lens portion for refracting said other portion of
light laterally of said luminaire.
3. The method of claim 2 wherein opposed lateral prismatic lens
portions are provided to spread portions of light other than
directed overhead away from both sides of said luminaire.
4. The method of claim 1 wherein said interior space includes at
least one vertical surface and wherein the light from said source
of indirect lighting is laterally refracted sufficiently to
illuminate at least the upper portion of said vertical surface.
5. The method of claim 1 wherein the upward directed portion of
light is dispersed by a lens media to provide a substantially
uniform pattern of luminance on the ceiling surface directly
overhead the source of indirect light.
6. A method of indirectly illuminating an interior space having a
ceiling surface comprising the steps of
(1) positioning a source of indirect light at a distance below said
ceiling surface, said source of indirect light including at least
one elongated luminaire having a light source, an elongated opaque
housing extending upward about said light source, and an elongated
lens means having an elongated lateral lens portion disposed
generally above said housing,
(2) directing a portion of the light from said light source upward
from said elongated housing to produce an elongated luminance
pattern on the ceiling surface directly overhead said housing,
and
(3) using said elongated lateral lens portion of said lens means to
refract substantially all of a portion of the light from said light
source laterally of said luminaire so as to spread same away from
said directly overhead luminance pattern to provide a laterally
extended overhead distribution of light.Iadd., and so that some of
said lateral spread of light is directed into viewing angles below
the indirect source of light whereby the source of indirect light
can be perceived by persons located below and to the side of said
source of indirect light.Iaddend..
7. The method of claim 6 wherein said interior space includes at
least one vertical surface and wherein said lateral lens portion is
used to refract a portion of light from said light source onto at
least the upper portions of said vertical surface.
8. The method of claim 6 wherein said elongated lens means is a
full lens cover over said housing and wherein a portion of light
from said light source is dispersed to the directly overhead
ceiling surface by the upper portion of said lens cover.
9. The method of claim 6 wherein two or more of said luminaires are
relatively widely spaced apart under said ceiling to produce a
substantially uniform luminance pattern between adjacent
luminaires.
10. The method of claim 6 wherein said luminaire is mounted to a
moveable partition.
11. The method of claim 8 wherein said luminaire is placed
approximately one foot below said ceiling surface.
12. The method of claim 6 wherein said luminaire is mounted on the
side of a vertical wall below said ceiling surface.
13. A method of indirectly illuminating an interior space having a
ceiling surface comprising the steps of
(1) positioning a source of indirect light at a distance below said
ceiling surface, said source of indirect light including at least
one luminaire having a light source, an opaque housing extending
upward about said light source to form at least one opaque
sidewall, and lens means having a lateral lens portion extending
generally upward from said opaque sidewall,
(2) directing a portion of the light from said light source upward
from said housing to provide a luminance pattern on the ceiling
surface directly overhead said housing, and
(3) using the upward extending lateral lens portion of said lens
means to refract substantially all of a portion of the light from
said light source laterally of said luminaire so as to spread same
away from said directly overhead luminance pattern to provide a
laterally extended overhead distribution of light.
14. The method of claim 13 wherein said lateral lens portion
spreads light to at least one adjacent vertical surface.
15. The method of claim 14 wherein said adjacent vertical surface
is illuminated by said lateral lens portion at eye level and
above.
16. The method of claim 13, 14, or 15 wherein said luminaire
housing and lens means are elongated.
Description
BACKGROUND AND SUMMARY
The present invention relates to a luminaire (i.e., the complete
lighting unit); and more particularly, it relates to a luminaire
which may be used for indirect lighting particularly in large open
areas such as are commonplace in modern offices. As will be further
explained below, one of the advantages of the invention is that its
use is not limited only to open office areas, but rather, it can be
carried through to the lighting of hallways, executive suites or
conference rooms. However, the invention is particularly suited to
provide illumination for typical office situations with efficient
use of energy while having those characteristics which recent
research has shown to be desirable from a psychological
viewpoint.
Modern offices are characterized by large open spaces having a
ceiling height normally about eight feet, but which may extend to
nine feet. The space may be sectioned for privacy by movable wall
partitions. These partitions normally have a height of about five
to seven feet.
In considering the lighting requirements for an office, among the
more important considerations are the need for individual task
lighting, for example, for surfaces approximately two and half feet
above the floor, and the need to provide some ambient lighting. The
latter is desirable both from a safety standpoint and for
psychological reasons, as will be discussed below.
Direct lighting as a source of lighting for offices provides high
luminance for task areas, but in general, the quality of lighting
is not good in terms of visibility and visual comfort of a
person.
Lenses have been used in luminaires employing fluorescent lamps for
direct lighting. One type of lens employs individual conical or
spherical lenses in a repeating pattern. Another uses parabolic
reflectors to direct light downwardly. In both of these systems, a
light transmission pattern is created in which the light is
directed downwardly and generally confined within an angle of about
45 degrees from the vertical. Further, neither of these systems
provides ambient lighting for vertical surfaces which has been
found to be a distinct preference and produces feelings of
spaciousness and comfort.
Indirect lighting obviates the problem of glare perceived by an
observer, but most indirect lighting systems have the disadvantage
of collecting dust which gathers on the lamps and any reflectors
beneath the lamps, and this is a major source of reduced luminance.
Another disadvantage of most indirect lighting systems is a
psychological one. Research has shown that human beings have a
distinct preference for lighter rooms which are uniformly
illuminated. In other words, a person may comfortably perform a
task in an area at a relatively low luminance level provided there
is a minimum of light available and the luminance pattern does not
change substantially within his field of view. If the luminance
level is substantially lower than that of the area from which a
person enters, there will be a period of adaptation, but once the
adjustment has been effected, there is little difficulty in
performing tasks if the illumination meets the minimum requirements
for the task. Further, people prefer to be able to see the source
of light. It provides a sense of perspective and has been found to
be a factor to be considered in providing office lighting. As
indicated, most indirect lighting systems have as a principal
object the generation of light while masking completely the origin
of the light.
Lenses have in the past placed above a source of light. Some of
these lenses do not generate a pattern of illuminance above the
luminaire which is uniform. Either a very bright spot is created
above the luminaire (the more common characteristic), or a dark
area is generated. In either case, the substantial variation in the
illumination pattern on the ceiling is easily perceived and is
undesirable. Further, in the case of the bright spot, inefficiency
results because most of the light is reflected back to the
luminaire rather than being used to light the room.
If a dark area is created on the ceiling, it is undesirable from an
aesthetic as well as a psychological viewpoint because of the
preferences mentioned above.
The method of the present invention has as a principal object the
provision of indirect lighting of large open office systems by
achieving a uniform distribution of light (i.e. illumination
pattern) on a ceiling over the luminaire as well as by fanning the
light out laterally to extend the uniform luminance on the ceiling
to adjacent areas not directly above the luminaire. Further, due to
the reinforcement and bending of lateral rays, vertical surfaces
are illuminated even at a substantial distance from the unit.
Particularly, the method of the invention provides for positioning
a source of indirect lighting below a horizontal ceiling surface of
an interior space, such as a large open office, and directing a
portion of the light from the source of indirect light upwardly to
produce a luminance pattern on the surface directly overhead the
light source. Another portion of light is redirected by refracting
it toward the horizontal so as to fan the source light outwardly
from the directly overhead luminance pattern. This laterally
refracted light extends from the directly overhead luminance
pattern on the horizontal ceiling, producing a laterally extended
light distribution pattern that is substantially uniformed and that
does not produce contrasting dark areas on the ceiling. The method
claimed herein can be achieved by lensed luminaires constructed in
the manner described and illustrated herein.
The described and illustrated luminaire includes an opaque housing
beneath the source of light which preferably includes two or three
fluorescent lamps placed side by side. The length of the lamps
helps to distribute the light along the length of the housing.
A lens is mounted to the housing above the source, and in the
illustrated embodiment, it includes a generally flat upper portion
and lateral portions which curve downwardly and join to the housing
to enclose the lamps. The upper portion of the lens includes a flat
upper surface and a series of light-diverging prisms on the lower
surface, facing the source of light. Adjacent prisms are spaced by
a flat portion. The function of the prisms is to refract and
diverge incident light, and the function of the flats is to permit
incident light to pass between the prisms. The prisms and flats
cooperate to provide a uniform pattern of luminance on a ceiling
above the luminaire which normally has a high reflectance to
provide good indirect lighting qualities. This uniformity is
effective when the ceiling is placed about two to three feet above
the upper surface of the lens and the effect persists even though
the spacing is reduced to one foot.
A reflector is located beneath the light sources in the housing to
direct light from the sources out to the lateral portions of the
lens. Some of the reflected light is transmitted upwardly to the
upper portion of the lens. In the illustrated embodiment there are
two lateral lens portions, but only one is necessary, for example,
if the luminaire is designed for placement directly on the side of
a vertical wall. The lateral lens portion or portions are curved
downwardly from the top lens portion to the upper edge of the
housing, and they contain a plurality of external prisms extending
the length of the lens.
The placement of the source of light in the housing is such that it
cannot be seen directly by an observer having an eye level the same
height as or slightly above the source. Further, because of the
interposition of the lens, the light source cannot be seen directly
from any elevation. The lateral lens portions bend the light from
the source as well as the light from the reflectors toward the
horizontal to "fan" the incident light and thereby extend the
uniform pattern of luminance onto portions of the ceiling not
directly above the luminaire. A pattern of luminance having
substantial uniformity is thus achieved on the ceiling directly
over-head and extending a few feet either side of the lens without
creating bright spots which cause glare or dark areas on the
ceiling, as characterized by some prior luminaires used for
indirect lighting. Thus, luminaires of the present invention may be
spaced at relatively wide distances if they are associated, for
example, with movable wall panels since adjacent luminaires will
both exhibit this fanning effect and achieve a luminance for
indirect lighting which not only provides uniform ambient lighting
but also more than adequate task lighting at the same time.
The fact that the light flux density diminishes as the distance
between the luminaire and the point being illuminated increases as
well as the fact that the flux density is reduced because the flux
density in a plane perpendicular to the source is spread over an
extended area for large angles of incidence (i.e. the angle
relative to the normal), as is the case for areas not directly
above the luminaire, are compensated by the effect of the reflector
which routes most of the light from the bottom of the source toward
the lateral lens portion, although some is transmitted to the top
lens portion because of the size of the lamps. This, as well as the
particular prism designs, disclosed below, cooperates to achieve a
pattern of substantially uniform luminance which is highly
desirable from a psychological standpoint and which achieves
uniform task light as well as ambient lighting while reducing the
amount of electricity to accomplish this in a large open office
area.
The lateral lens portions of the luminaire transmit direct and
reflected light from the source to illuminate vertical surfaces
such as walls and provide a brighter ambient lighting.
Other objects and advantages of the method of the invention will be
apparent to persons skilled in the art from the following detailed
description of a luminaire capable of illuminating in an interior
space in accordance with the method of the invention.
THE DRAWINGS
FIG. 1 is a side elevational view of a typical movable panel wall
system on which a luminaire constructed according to the present
invention is mounted;
FIG. 2 is an upper side perspective view of the luminaire of FIG.
1;
FIG. 3 is a transverse cross sectional view of the luminaire of
FIG. 2;
FIG. 4 is a fragmentary longitudinal vertical cross sectional view
of one end of the luminaire of FIG. 2; and
FIG. 5 is a diagrammatic cross sectional view of the right side of
a lens incorporated into the luminaire of FIG. 2.
DETAILED DESCRIPTION
Referring first to FIG. 1, reference numeral 10 generally
designates a movable wall panel at the top of which a luminaire
generally designated 11 is mounted by means of an upright mount 12
extending from the top of the panel 10. The mount 12 may take the
form of a pair of upright arms enclosed in a sheet metal
casing.
To illustrate the type of task lighting to which the present
invention is directed, a cabinet generally designated 13 may be
mounted to the wall panel 10, and a work surface 14 may be provided
beneath the cabinet 13.
Turning now to FIG. 2, the fixture 10 is seen to include a housing
15, first and second end caps 17, 18, and an upper lens 19.
As best seen in FIG. 3, the housing 15 includes a generally flat
bottom wall 21 and upwardly curved side walls 22, 23. The housing
15 may be formed by extruded aluminum since its cross section is
uniform throughout. It is then cut to the desired length.
On the side wall portion 22, there is formed a screw mount 25, and
a similar screw mount 26 is formed on the inner surface of the side
wall 23. First and second inwardly extending lips 27, 28 are formed
at the upper edges of the side walls 22, 23 respectively.
A reflector generally designated 30 is mounted in the housing 15 by
screws 31 secured in the screw mounts 25, 26. The reflector 30 is
symmetrical about a vertical plane P extending through the
longitudinal center of the luminaire to form side halves 33, 34.
Thus, the side 33 includes a flat portion 35 beneath a first lamp
L1; and to the side of the lamp L1, the reflector is smoothly
curved upwardly to form a portion 36, the edge of which is formed
into a mounting flange 37. The central portion of the reflector is
turned upwardly as at 39. The surface of the reflector may vary
according to the effect desired, but for general office use, a
specular surface may be used.
The illustrated embodiment includes a second lamp L2 located within
the housing 22. Both lamps are mounted between a pair of
conventional lamp holders, one of which is shown in FIG. 3 at 39
mounted to a first intermediate wall 40. A third lamp may be used
by moving the two lamps shown further apart and inserting a third
lamp between them. The center lamp would be raised slightly. The
luminaire may also be used with only a single lamp or with a switch
for illuminating one, two or three lamps, as desired.
A lens generally designated 41 is mounted to the housing 15 by
means of first and second elongated fittings 44, 45 which
releasably couple respectively to the inwardly extending lips 27,
28 of the housing 15. Thus, the lens is mounted in such a manner
that it can be removed easily, simply by pressing the sides, yet it
prevents dust and dirt from entering the interior of the luminaire.
The end seals will be described in connection with FIG. 4.
The lens 41 includes an upper lens portion 48, and first and second
curved lateral portions 49, 50. The lens 41 is also symmetrical
about the plane P. Because both side halves of the fixture operate
in a similar manner, the features and advantages of the invention
can be achieved simply be extending the housing along the plane P
for a luminaire adapted to mount to the vertical surface of a wall,
such as in a hall or conference room, as distinguished from the
bottom-mounted luminaire shown.
Referring now to FIG. 4, the end cap 17 is seen in detail. It is
received on and held to an intermediate wall 53 which serves to
mount the lamps and also to support a ballast B in the manner
illustrated. Thus, the end cap 17 cooperates with the intermediate
wall 53 to provide a housing for the ballast B which may be mounted
by means of a flexible grommet 55 to a platform 56 cantilevered
from the intermediate wall 53 to reduce noise transmission from the
ballast B.
In FIG. 4, there is also shown a gasket 58 which seals the left
edge of the lens 41 against the entry of dust into the interior of
the luminaire. A similar gasket is provided on the other
intermediate wall 40.
Turning now to FIG. 5, which illustrates the structure of one side
of the lens 41 in relation to the center of lamp L1, designated 60
in FIG. 5, the top portion 48 of the lens has a flat upper surface
designated 61. This facilitates dusting of the fixture and provides
no crevices for collecting dust or dirt. The under surface of the
top portion 48 of the lens 41 is formed into a plurality of
equalateral prisms 62 which extend the length of the lens, and are
separated by flat portions or simply "flats" designated 63.
The principal function of the prisms 62 is to cause incident light
to diverge through refraction. Consider, for example, parallel
incident rays 65, 66 which are incident respectively on the surface
62A and 62B. The ray 65 is refracted and travels along the path 67
through the transparent material of the lens to the upper exit
surface 61 thereof where it is again refracted ray 66 follows the
path 69 in the lens and emerges along the path 70 from the exit
surface 61. Thus, the light which is incident on the surfaces of
the prisms 62 is widely dispersed and diverged through
refraction.
Light which is incident on one of the flats 63, on the other hand,
is simply displaced but remains parallel to the path of the
original incident ray. Consider, for example, the ray 72 which is
incident on a land designated 63A. It travels along a path 73
within the lens material, but emerges from the exit surface 61 to
travel along a path 74 which is parallel to the path of the
original ray 72. Because of the size, configuration and spacing of
the prisms, the light emerging from the exit surface 61 is diverged
in such a manner that the resulting pattern of luminance on a
horizontal surface above the luminaire for as close a spacing as
one foot is substantially uniform without either bright or dark
areas.
In a preferred embodiment, the angle of each of the prisms 62 is 60
degrees; and the height h' is 30 mils. The spacing d' of the prisms
is 62 mils, and the thickness of the lens 41 between the exit
surface 61 and the flats 63 is 130 mils. These dimensions can be
changed without any appreciable change in the results. If the
proportion of prisms height to spacing remains the same, the
results will be the same. The material of the lens preferably is
clear virgin acrylic, although other materials such as Lexon may
also be used.
Turning now to the lateral portion 50 of the lens, its principal
function is to bend incident light from the source and to "fan" the
light out laterally so that it is spread to the side of the fixture
on a ceiling and may also be used to illuminate any vertical
surfaces in the neighboring vicinity. Because of the reduction in
intensity due to the greater distance traveled by the light passing
through the lateral portion 50 as well as the fact that the flux
will be spread over a greater area of any illuminated horizontal
surface due to the increased angle of incidence, a principal
function of the reflector 30 and particularly the curvature of the
portion 36 is to direct light from the source L1 toward the lateral
portion 50 of the lens.
The lateral lens portion 50 of the lens has a uniformly curved,
smooth interior surface 80 which has a radius of curvature R
centered at 81. The outer surface of the lateral portion 50 of the
lens is formed into a plurality of prisms, the points of which are
designated respectively P1-P21 for convenience.
Each of the prisms P1-P21 includes an active or emitting surface
such as that designated 84 for the prisms P3 from which light
incident on the inner surface 80 will emerge, and a second surface
85 referred to as a riser or return surface. The structure of the
prisms P1-P21 is illustrated in Table I where the angles RHS, LHS,
LHS-1 and LHS-2 are defined in FIG. 5. The dimension "h" is the
height of a prism. The nominal thickness of the lateral portion 50
from the uniformly curved surface 80 to the intersection between an
adjacent riser 85 of one prism and the active surface of the
adjacent prism is 125 mils. Further, the center 60 of the light
source is approximately 0.625 inches below the center 81 of the
radius of curvature of the surface 80, and approximately two inches
to the left of it. It will also be observed that the center 81 is
in approximately the same horizontal plane as the upper extension
of the curved side 22 of the opaque housing 15. Thus, the light
sources cannot be seen directly by an observer whose eye level is
the same height as the source.
Because the luminaires are preferably mounted at a height of six to
seven feet above the floor (that is, the height to the top of the
side wall 22 of the housing 15), a person who is less than about
seven feet tall will have a line of sight which will be above the
lamps. However, as will be explained presently, he will perceive
where the light is coming from.
Still referring to FIG. 5, three light rays are designated 90, 91
and 92; and for purposes of illustration, they are shown as
emanating from the center 60 which is an idealized point. In the
medium of the lens, the rays take the respective paths 90A, 91A and
92A; and when they exit from the associated active surfaces of the
prisms as illustrated, they travel along the paths 90B, 91B and 92B
respectively. It can thus be seen that the light from the source is
spread out in an increasing pattern from the top to the side edge
of the lateral portion 50 of the lens. Further, it is segmented in
the sense that an observer viewing the lens from the side at normal
angles will see a series of softly glowing horizontal lines and
therefore perceive where the light is emanating from. Not
illustrated in FIG. 5 for clarity are the rays of light emanating
from the source L1 which are reflected by the reflector 30 and
directed toward the lateral portion 50 of the lens. As indicated,
these rays reinforce the direct rays from the source so that the
pattern of luminance on a horizontal surface above the fixture will
be substantially uniform and without glare spots or dark areas not
only directly above the luminaire but also for a distance of
several feet to the side thereof. By providing uniform ambient
lighting, as mentioned above, the overall luminance can be
maintained at a relatively low level and yet provide adequate task
lighting. By bending the light and fanning it out laterally through
the lateral portions of the lens, the luminaires can be placed at
relatively greater distances than would otherwise be required to
achieve complete illumination coverage and uniform luminance.
Vertical surfaces in a room employing these luminaires are also
illuminated in a substantially uniform manner even at eye level and
above, because of light directed from the lateral lens portions and
reflected off the ceiling. As mentioned, human perception of
whether a room is adequately lighted depends to some extent on
whether the vertical surfaces are visibly illuminated.
Still further, it will be appreciated that the lens acts as a dust
cover to prevent dust and dirt from reducing the luminance
emanating from the source, and because of the upper surface of the
top portion of the lens is flat, it facilitates cleaning. It will
be observed that at least some light emanates from the riser
surfaces of the prisms on the lateral portion of the lens, and this
light is directed downwardly below the horizontal. It may not be
enough light to provide adequate task lighting but it nevertheless
provides a visual image to an observer seated at a work area so
that he can see where the light is coming from.
Having thus described in detail a preferred embodiment of the
invention, persons skilled in the art will be able to modify
certain of the structure which has been illustrated and substitute
equivalent elements for those disclosed while continuing to
practice the principle of the invention. For example, the
dimensions of the lens may be altered without substantially
changing the photometric properties of the luminaire, particularly,
if the height-to-spacing proportions of the various prisms is
maintained. Further, although fluorescent lamps are preferred,
other lamps may also be used; and lamps not yet developed may have
equal or better results. Finally, the number of lamps or type of
ballast are not critical to achieving the overall desired results.
It is, therefore, intended that all such modifications and
substitutions be covered as they are embraced within the spirit and
scope of the appended claims.
TABLE I ______________________________________ Point 1 2 3 4 5 6 7
______________________________________ RHS 0 0 0 0 0 0 0 LHS 63.9
65.2 66.4 67.6 68.8 70.0 71.1 h .070 .067 .063 .060 .057 .054 .066
______________________________________ POINT 8 9 10 11 12 13 14
______________________________________ LHS-1 24.1 33.3 33.3 33.3
33.3 12.1 9.8 LHS-2 69.0 69.0 69.0 69.0 67.8 70.4 73.0 h .082 .082
.082 .082 .070 .058 .047 ______________________________________
POINT 15 16 17 18 19 20 21 ______________________________________
RHS 0 0 0 0 -- 87.2 82.5 LHS 70.0 74.3 78.8 83.4 -- 0 1.25 h .054
.044 .034 .017 -- .017 .025
______________________________________
* * * * *