U.S. patent number 3,679,893 [Application Number 05/069,344] was granted by the patent office on 1972-07-25 for luminaire reflector comprising elliptical and parabolic segments.
This patent grant is currently assigned to Sylvan R. Schemitz and Associates, Inc.. Invention is credited to Sylvan R. Shemitz, Benjamin L. Stahlheber.
United States Patent |
3,679,893 |
Shemitz , et al. |
July 25, 1972 |
LUMINAIRE REFLECTOR COMPRISING ELLIPTICAL AND PARABOLIC
SEGMENTS
Abstract
Substantially uniform magnitude of illumination on a plane
surface is provided by a concave reflector having a parabolic
reflecting surface and an elliptical reflecting surface oriented
relative to one another to satisfy the following criteria. A. the
first focal point of the elliptical surface is on the axis of the
parabolic surface, B. the second focal point of the elliptical
surface is not within the closure formed by the inner surfaces of
the reflecting surfaces and a plane across the outwardly extending
edges of the surfaces, C. the axis of the parabolic surface is from
about 45.degree. to about 90.degree. from nadir, and D. the major
axis of the elliptical surface is from about 5.degree. to about
45.degree. from nadir. Preferred embodiments include the parabolic
surface and elliptical surface separated by one or more general
reflecting surfaces, and the same combinations of surfaces with a
second parabolic reflecting surface or flat reflecting surface
adjacent and below the first parabolic surface and a flat
reflecting surface adjacent and outside of the elliptical surface.
The additional surfaces provide further improvement in control of
the reflections.
Inventors: |
Shemitz; Sylvan R. (Woodbridge,
CT), Stahlheber; Benjamin L. (Clinton, CT) |
Assignee: |
Sylvan R. Schemitz and Associates,
Inc. (West Haven, CT)
|
Family
ID: |
22088341 |
Appl.
No.: |
05/069,344 |
Filed: |
September 3, 1970 |
Current U.S.
Class: |
362/345;
362/350 |
Current CPC
Class: |
F21V
7/09 (20130101); F21W 2131/107 (20130101); F21Y
2103/00 (20130101) |
Current International
Class: |
F21V
7/09 (20060101); F21V 7/00 (20060101); F21v
007/09 () |
Field of
Search: |
;240/2B,7.1C,25,41.35R,41.35C,41.35E,41.35F,41.37,44,44.1,51.11,103,104 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
669,180 |
|
Mar 1952 |
|
GB |
|
885,071 |
|
Dec 1961 |
|
GB |
|
1,249,905 |
|
Nov 1960 |
|
FR |
|
471,347 |
|
May 1969 |
|
CH |
|
Primary Examiner: Queisser; Richard C.
Assistant Examiner: Snee, III; C. E.
Claims
What is claimed is:
1. In a concave reflector, the combination of:
1. a first reflecting surface parabolic in section,
2. a second reflecting surface elliptical in section, said surfaces
being positioned relative to each other such that:
a. the first focal point of said elliptical surface is on the axis
of said parabolic surface,
b. the second focal point of said elliptical surface is not within
the closure formed by said reflecting surfaces and a plane across
the outwardly extending edges of said surfaces,
c. the axis of said parabolic surface is from about 45.degree. to
about 90.degree. from nadir, and
d. the major axis of said elliptical surface is from about
5.degree. to about 45.degree. from nadir, and
3. means adjacent the outer rim of said first reflecting surface,
for reflecting first reflections from said elliptical surface, when
substantially all of said first reflections are not reflected into
the -10.degree. to +65.degree. zone from nadir, into said zone;
whereby, when a light source is placed at said first focal point,
light is reflected from said concave reflector in an asymmetric
pattern to produce substantially constant magnitude of illumination
on a plane and to reduce discomfort glare and disability veiling
glare.
2. A concave reflector as in claim 1 wherein reflecting means (3)
is a parabolic surface the axis of which passes through the second
focal point of said elliptical surface.
3. A concave reflector as in claim 2 including at least one flat
reflecting surface adjacent the outer rim of said reflecting means
(3), so disposed as to reflect into the zone encompassed by
-10.degree. to +65.degree. from nadir.
4. A concave reflector as in claim 2 wherein, on a compass having
as its origin the first focal point of said second reflecting
surface, said first reflecting surface in section extends from
212.degree. to about 288.degree., said second reflecting surface in
section extends from about 44.degree. to about 110.degree., and
said reflecting means (3) in section extends from about 192.degree.
to about 212.degree..
5. A concave reflector as in claim 4 including three general
reflecting surfaces disposed between said first and second
reflecting surfaces, one of said general reflecting surfaces in
section extending from about 287.degree. to about 308.degree., the
second of said general reflecting surfaces in section extending
from about 308.degree. to about 338.degree., and the third general
reflecting surface in section extending from about 2.degree. to
about 44.degree., the space between the second and third general
reflecting surfaces being a ventilation slot.
6. A concave reflector as in claim 5 including at least one flat
reflecting surface in section extending from about 187.degree. to
about 192.degree..
7. A concave reflector as in claim 1 including a general reflecting
surface disposed between said first and second reflecting surfaces
so as to reflect into the zone encompassed by -10.degree. to
+65.degree. from nadir.
8. A concave reflector as in claim 7 wherein, on a compass having
as its origin the first focal point of said second reflecting
surface, said first reflecting surface in section extends from
about 197.degree. to about 238.degree., said second reflecting
surface in section extends from about 0.degree. to about
84.degree., and said general reflecting surface in section extends
from about 242.degree. to about 343.degree..
9. A concave reflector as in claim 1 wherein reflecting means (3)
is a first flat reflecting surface.
10. A concave reflector as in claim 1 including a flat reflecting
surface adjacent the outer rim of said second reflecting surface,
so disposed as to reflect into the zone encompassed by -10.degree.
to +65.degree. from nadir.
11. A concave reflector as in claim 1 wherein reflecting means (3)
is a parabolic surface, the axis of which passes through the second
focal point of said elliptical surface, said concave reflector
further including at least one general reflecting surface disposed
between said first and second reflecting surfaces so as to reflect
into the zone encompassed by -10.degree. to +65.degree. from
nadir.
12. The concave reflector of claim 11 wherein the general
reflecting surface is in three portions separated by a ventilation
slot between two of said portions.
13. A concave reflector as in claim 1 wherein reflecting means (3)
is a first flat reflecting surface, said first flat reflecting
surface in section extending from about 180.degree. to about
198.degree., said concave reflector further including a second flat
reflecting surface adjacent the outer rim of said second reflecting
surface, said second flat reflecting surface in section extending
from about 88.degree. to about 101.degree..
14. In a luminaire, the combination of: a concave reflector as in
claim 1, a housing for said reflector, means for supporting said
reflector in said housing, and a light source placed at said first
focal point of said elliptical surface.
15. A concave reflector as in claim 1 wherein said reflecting means
(3) is a first flat reflecting surface; said concave reflector
further including a general reflecting surface between said first
and second reflecting surfaces, and a second flat reflecting
surface adjacent the outer rim of said second reflecting surface,
said general reflecting surface and said second flat reflecting
surface each being positioned so as to reflect into the zone
encompassed by -10.degree. to +65.degree. from nadir.
16. A concave reflector as in claim 15 wherein, on a compass having
as its origin the first focal point of said second reflecting
surface:
said first reflecting surface in section extends from about
197.degree. to about 238.degree.;
said second reflecting surface in section extends from about
0.degree. to about 84.degree.;
said first flat reflecting surface in section extends from about
180.degree. to about 198.degree.;
said second flat reflecting surface in section extends from about
88.degree. to about 101.degree.; and
said general reflecting surface in section extends from about
242.degree. to about 343.degree..
17. A concave reflector as in claim 1 wherein said reflecting means
(3) is a parabolic surface the axis of which passes through the
second focal point of said second reflecting surface; said concave
reflector further including at least one general reflecting surface
between said first and second reflecting surfaces, and at least one
flat reflecting surface adjacent the outer rim of said reflecting
means (3), said general reflecting surface and said flat reflecting
surface each being positioned so as to reflect into the zone
encompassed by -10.degree. to +65.degree. from nadir.
18. A concave reflector as in claim 17 wherein the general
reflecting surface is in three portions separated by a ventilation
slot between two of said portions.
19. A concave reflector as in claim 17 wherein, on a compass having
as its origin the first focal point of said second reflecting
surface:
said first reflecting surface in section extends from about
212.degree. to about 288.degree. ;
said second reflecting surface in section extends from about
44.degree. to about 110.degree. ;
said reflecting means (3) in section extends from about 192.degree.
to about 212.degree. ;
said general reflecting surface is in three portions, one of said
portions in section extending from about 287.degree. to about
308.degree., the second in section extending from about 308.degree.
to about 338.degree. and the third in section extending from about
2.degree. to about 44.degree., the space between the second and
third portions being a ventilation slot; and
said flat reflecting surface is in two portions, together in
section extending from about 185.degree. to about 192.degree. .
Description
BACKGROUND OF THE DISCLOSURE
This invention relates to concave reflectors and luminaires for use
in asymmetric light distribution.
It is known from the inverse square law with its cosine correction,
E =(I/d.sup.2) cos .theta., defining the magnitude of illumination
E at a point on a plane, that equality of the illumination at all
points on the plane theoretically requires that a luminaire provide
thirteen times more candlepower at a point approximately 2.15 times
mounting height away on the plane to be illuminated than is
provided at nadir. Despite this understanding of an essential
requirement for controlled, uniform illumination, attempts to
design luminaires to approach these results have not been entirely
successful. A primary reason for the lack of success has been
inability to control both the direct and reflected emanations from
a light source so as to substantially eliminate light losses caused
by subtraction of light rays, by reflection of light rays back to
the light source, and by stray reflections. When a large proportion
of the light rays are reflected back to the source, the problem is
complicated by excessive heat production within the source.
In addition to constant magnitude of illumination along the plane,
it is preferred that sharp cutoff of rays on each side of the plane
to be illuminated be provided in order to conserve and concentrate
the light flux.
Another requirement is the reduction of discomfort glare and
disability veiling glare when the observer is within or without the
zone of illumination. Reduction of glare is especially important,
for example, when the luminaire is to be employed for the
illumination of airport aprons and vehicular or pedestrian
walkways. Designs, however, which have reduced glare have done so
by means of visors, baffles, or absorbers placed within or external
to the closure of the luminaire, but to the detriment of
continuously even illumination and with greater expense of
manufacture.
Coupled with the foregoing requirements is the need for a luminaire
which can be preset, or which is later adjustable, in order to
provide a portion of the illumination of constant magnitude to an
extension of the plane to be illuminated in the direction opposite
to the major portion of the plane being illuminated, that is, into
the zone encompassed by negative degrees from nadir, e.g.,
-10.degree. from nadir. For example, it is sometimes important to
be able to illumine two planes which are separated by a normal to
the light source where one of the planes is substantially longer
than the other. This situation is illustrated by a street light
placed elevated on a support between a sidewalk and a street, the
latter having substantially greater width than the former. Ideally,
in this circumstance, the luminaire should illuminate with the same
magnitude of illumination the full width of the street as well as
the narrower width of the sidewalk but without wasting light by
illuminating areas outside of the sidewalk and street. Thus, not
only should the luminaire be capable of illuminating both the
street and sidewalk without glare, but the luminaire should also
provide a sharp cutoff of the illumination at the outer boundaries
of the sidewalk and street. This capability permits a luminaire to
be mounted on a short projection or arm, as from a pole or from the
side of a structure, since the luminaire can light the zone on the
negative side of nadir, that is, the shorter portion of the
horizontal plane as well as the longer portion of the horizontal
plane.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a new and
improved concave reflector or luminaire which is capable of
illuminating a surface with substantially constant magnitude
through an asymmetric distribution.
A further object is to provide a new and improved reflector and
luminaire capable of controlling the direction of emanations from
the light source so as to substantially eliminate light losses.
A still further object is to provide a concave reflector and
luminaire for asymmetric light distribution, which is capable of
sharply cutting off the illumination on each end of the plane to be
illuminated.
Another object is to provide a new and improved concave reflector
capable of reducing glare in the eyes of an observer positioned
within or without the zone of illumination.
An additional object is to provide a new and improved reflector and
luminaire which may be adapted to encompass selected portions of
the zones on each side of nadir when forming an asymmetric pattern
of illumination.
Still other objects, features and advantages of the invention will
in part be obvious and will in part be apparent from the
specification.
In brief outline, it has been discovered that when properly
oriented relative to each other, a reflecting surface which is
parabolic in section and a reflecting surface which is elliptical
in section in combination provide a concave reflector substantially
satisfying the foregoing objectives. Conditions which define the
orientation of the two essential reflecting surfaces of the
invention are as follows:
a. the first focal point of the elliptical surface is on the axis
of the parabolic surface,
b. the second focal point of the elliptical surface is not within
the closure formed by the reflecting surfaces and a plane across
the outwardly extending edges of the surfaces,
c. the axis of the parabolic surface is from about 45.degree. to
about 90.degree. from nadir, and
d. the major axis of the elliptical surface is from about 5.degree.
to about 45.degree. from nadir.
When substantially all of the first reflections from the elliptical
surface are not reflected into the -10.degree. to +65.degree. zone
from nadir, additional reflecting means adjacent the outer rim of
the parabolic surface for reflecting these reflections into the
-10.degree. to +65.degree. zone from nadir, are employed.
With respect to criterion (d), the orientation of the elliptical
surface, such that its major axis is less than 35.degree. from
nadir, will cause reflections from the elliptical surface to
illuminate areas on the negative side of nadir. When the elliptical
surface is so oriented, it may then be useful or necessary to
recapture its reflections and reflect them into the zone on the
0.degree. to 65.degree. side of nadir. This is achieved by the
additional reflecting means, as explained below.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the
scope of the invention will be indicated in the claims.
DETAILED DESCRIPTION
With reference to the drawings:
FIG. 1 is a perspective, partially fragmentary, view of a concave
reflector of the invention;
FIG. 2 is an elevational section along line 2--2 of FIG. 1;
FIG. 3 is a diagrammatic elevational view of a reflector of the
invention positioned to provide asymmetric light distribution on a
vertical plane;
FIG. 4 is a diagrammatic view of the reflections from a reflector
of the invention;
FIG. 5 is a photometric curve (relative candlepower) in a vertical
plane through a reflector and luminaire of the invention;
FIG. 6 is a diagrammatic view of the reflections from another
reflector of the invention; and
FIG. 7 is a photometric curve (relative candlepower) in a vertical
plane through the reflector and luminaire of FIG. 6.
In the embodiment of the invention illustrated in FIGS. 1 to 4, a
concave reflector 11 essentially comprises a reflecting surface 13
which is parabolic in section, and a reflecting surface 15 which is
elliptical in section. Reflectors 13 and 15 are shown separated by
a reflecting surface 17 which, in section, is a general curve.
Adjacent the outside rim of the elliptical surface 15 is a flat
reflecting surface 19, forming a straight line in section. Below
and on the outside rim of parabolic surface 13 is a second flat
reflecting surface 21, forming a straight line in section.
Reflecting surface 17 is shown slightly outside of surfaces 13 and
15 so as to form vents 23 and 25 therebetween. A light source 27 is
placed at the first focal point F.sub.1 of the elliptical surface.
Reflector 11 may be enclosed in a housing such as 29 and fixed
therein by means such as struts, rivets, bolts, or the like (not
shown), behind a protective window or lens such as glass 31.
FIG. 3 illustrates the reflector 11 in position on horizontal
surface 35 for illumination of a vertical plane 33 such as a
billboard. It should be understood that the plane 33 might also
represent a horizontal surface, reflector 11 then being positioned
above the horizontal surface, preferably on a vertical support
member, now represented by 35, for illumination of the surface. In
either position, the reflector of the invention provides
substantially constant magnitude of illumination over the plane 33
in the 0.degree. to 65.degree. zone from nadir, shown as angle A.
The maximum practical extent of angle A is 65.degree., although it
may be varied to more or less than 65.degree. by selecting
additional reflecting surfaces for use with the parabolic and
elliptical surfaces or by rotating or tilting the surfaces.
The direction of reflections from the individual surfaces and
operation of the reflector 11 as a whole is evident from a
consideration of FIGS. 4 and 5. With reference to FIG. 4, it will
be noted that the two essential reflecting components 13 and 15 are
defined as to their curvature and relative orientation in space by
the following criteria:
a. the first focal point of the elliptical surface is on the axis
of the parabolic surface, and preferably coincides with the focal
point of the parabolic surface,
b. the second focal point of the elliptical surface is not within
the closure formed by the reflecting surfaces and a plane across
the outwardly extending edges of the surfaces,
c. the axis of the parabolic surface is from about 45.degree. to
about 90.degree. from nadir, preferably about 65.degree. as shown
in FIG. 4, and
d. the major axis of the elliptical surface is from about 5.degree.
to about 45.degree. from nadir, preferably about 45.degree. as
shown in FIG. 4.
The closure referred to in (b) is line PP' in FIG. 4. It will be
noted that the second focal point F.sub.2 is below line PP' and
therefore outside of the closure. With reference to criterion (c),
it will be noted that line 37 is on the axis of parabolic surface
13, and line 37 passes through the first focal point F.sub.1 of
elliptical surface 15. Illuminations from surfaces 13 and 15 are
indicated on plane 33 as sectors 33a and 33b respectively. While
surfaces 13 and 15 may be positioned such that some overlap occurs
on plane 33 between their reflections, it is preferred that
surfaces be chosen and oriented so as to avoid overlap, as
illustrated.
While it is possible to rely only upon the combination of a
parabolic reflecting surface 13 and an elliptical reflecting
surface 15, in order to provide illumination of the desired
characteristics on plane 33, it is preferred to employ in
conjunction with the two essential surfaces at least a general
reflecting surface 17 for the purpose of reinforcing the
reflections from the two essential surfaces, avoiding reflections
back to the light source, and for filling in the areas between the
reflections from the surfaces on the plane to be illuminated, as
shown in FIG. 4 with respect to reflections along the entire length
of plane 33, including 33a and 33b. General reflecting surface 17
may take any suitable form, such as a flat surface, spherical,
parabolic, or general surface.
As the auxiliary reflecting means, especially for reflecting direct
emanations into the useful zone as well as for redirecting stray
reflections from the other surfaces, there may be employed
reflecting surfaces such as flat surfaces 19 and 21 as shown in
FIG. 4. An additional function of these auxiliary surfaces 19 and
21 is to enhance the sharp cutoff of the reflections onto plane 33
at predetermined angles. For example, as shown in FIG. 4,
reflecting surface 21 provides sharp cutoff of direct emanations
from source 27 so that illumination on plane 33 begins at 0.degree.
from nadir. However, as indicated by discontinuous line 38,
subtended by angle B, illumination in a negative direction from
nadir may be provided by employing a reflecting surface 21 which
does not cut across or touch the normal (y axis) to plane 33.
In FIG. 4, the major axis F.sub.1 F.sub.2 of the elliptical surface
15 is about 45.degree. from nadir. With this orientation,
substantially all of the reflections from elliptical surface 15 are
on plane 33 in the 0.degree. to 65.degree. zone from nadir.
However, as will be evident from FIGS. 6 and 7, should the major
axis of the elliptical surface be oriented such that reflections
therefrom are not directed into the zone defined by -10.degree. to
+65.degree. from nadir, an auxiliary reflecting surface may be
employed in order to redirect these reflections into the
-10.degree. to +65.degree. zone.
FIG. 5 shows the approximate relative candlepower distribution
provided by the embodiment of FIGS. 1-4 onto plane 33. As is well
known, the resulting "half bat wing" shaped curve indicates
substantially even distribution of illumination on plane 33, that
is, illumination of substantially constant magnitude. It will
further be noted that some distribution of the illumination is
shown in the region to the left of nadir, in the zone encompassed
by angle B. The extent of this distribution is governed by the
relative orientation of the parabolic and elliptical surfaces of
the reflector as well as by the extent to which auxiliary
reflecting surfaces, such as surface 21, are employed. It should be
evident, however, that the major proportion of the illumination is
into the region to the right of nadir when the major axis of the
elliptical surface is about 35.degree. or more from nadir, and
therefore the resulting photometric curve would still approximate
the curve of FIG. 5. The magnitude of the area 41 will depend on
the output of light source 27, but the shape of the curve will be
constant for the same reflector and same light source position.
A preferred arrangement of reflecting surfaces of the reflector and
luminaire of the invention relative to plane 33 may be described on
the compass shown in FIG. 4 in which the first focal point F.sub.1
of the elliptical surface is placed at the origin, this also being
the placement of the light source. The x and y axes thus define
four quadrants I, II, III, and IV. Taking the y axis to the left of
F.sub.1 in FIG. 4 as north, the preferred positions of the
reflecting surfaces of FIG. 4 may be defined as follows:
1. Parabolic surface 13 is closer to plane 33 than is elliptical
surface 15.
2. The second focal point F.sub.2 is outside the closure perimeter
PP', and F.sub.1 and the focal point of parabolic surface 13
coincide.
3. The parabolic surface 13 in section extends from 197.5.degree.
to 237.5.degree..
4. The elliptical surface 15 in section extends from 0.degree. to
83.5.degree..
5. The general surface 17 in section extends from 242.5.degree. to
342.5.degree..
6. The lower flat surface 21 in section extends from 180.degree. to
197.5.degree..
7. The upper flat surface 19 in section extends from 88.5.degree.
to 100.5.degree..
8. The ventilation slots 23, 25 and 26 occur at 350.degree.,
240.degree. and 85.degree., respectively.
9. The axis 37 of parabolic surface 13 is in the range 90.degree.
to 135.degree. (90.degree. to 45.degree. from nadir) preferably
115.degree. to 120.degree. (65.degree. to 60.degree. from nadir),
and passes through F.sub.1.
10. The major axis F.sub.1 F.sub.2 of elliptical surface 15 is at
135.degree. (45.degree. from nadir).
The elliptical surface 15 in section may be extended past
83.5.degree. to 103.5.degree. to provide maximum reflection of
light in a left and down direction with respect to plane 33. When
so extended, the lower flat reflecting surface 21 may start at
181.5.degree. rather than at 180.degree..
FIG. 6 shows a particularly preferred embodiment of reflectors and
luminaires of the invention. With reference thereto, the essential
reflecting surfaces are a reflecting surface 43 parabolic in
section and a reflecting surface 45 elliptical in section. With
respect to the relative orientations of these two surfaces, it will
be noted with reference to FIG. 6 that the four criteria set forth
above are fully satisfied. Particularly, it will be noted that the
second focal point F.sub.2 of elliptical surface 45 is on but not
within the closure PP' of the reflector. Further, it will be noted
that the axis of parabolic surface 43, represented by line 67,
passes through the first focal point F.sub.1 of elliptical surface
45 and the light source 27 is placed at the first focal point
F.sub.1 of elliptical surface 45. Preferably, as shown, F.sub.1 and
the focal point of parabolic surface 43 coincide.
In the orientation of surfaces 43 and 45 of FIG. 6 it will be noted
that the light rays reflected from elliptical surface 45, after
passing through second focal point F.sub.2, are directed to
quadrant III of the compass defined by F.sub.1 as origin and the y
axis to the left as north. In order to redirect these reflections
into the 0.degree. to 65.degree. zone from nadir, an auxiliary
reflecting surface 47, parabolic in section, is employed. While
surface 47 preferably is parabolic, it will be evident that other
surfaces such as a flat reflecting surface, a general reflecting
surface, or other surfaces, may be employed.
With reference to FIG. 6, it will be noted that the reflections
from parabolic surface 43 illuminate the sector 63a on plane 63 and
the re-reflected rays from elliptical surface 45 illumine the
sector 63b on plane 63 with substantially no overlap between the
reflections. In order to reinforce these illuminations and to
control the direct emanations from light source 27, general
reflecting surfaces 53, 54 and 56 are mounted adjacent to and above
reflecting surfaces 43 and 45, relative to surface 63. These
general surfaces also serve to illuminate sectors on plane 63 not
illuminated by surfaces 43 and 45, such as sector 63c. As so
constituted, a reflector of FIG. 6 would also illuminate a small
region to the left of nadir bounded by discontinuous line 68.
However, for some applications, it may be preferred to provide a
sharp cutoff at 0.degree. nadir or at a position on the positive
side of nadir. For this purpose one or more flat reflecting
surfaces or baffles, shown in section as straight lines 49 and 51,
may be employed.
In the embodiment of FIG. 6, a ventilating slot 57 is provided as a
convenience between surfaces 54 and 56, although it should be
understood that the slot may be provided at any point on the
reflector in the vicinity of light source 27 in order to prevent
overheating. It will be evident that reflecting surfaces 53, 54 and
56 may be eliminated and the two essential reflecting surfaces 43
and 45 extended to close the resulting gap, or a vent 57 may be
maintained between surfaces 43 and 45.
FIG. 7 illustrates photometrically the approximate relative
candlepower distribution provided by a reflector and luminaire as
illustrated in FIG. 6. "Relative candlepower" and the angles A and
B have the same meaning as in FIG. 5. It will be evident from the
shape of the curve that the ideal light distribution for uniform
illumination has been substantially achieved within the zone
encompassed by about 0.degree. to about +65.degree. from nadir, the
perfect curve being a straight line paralleling the bottom line of
the curve. Similar to FIG. 5, the shape of the curve will be
constant for identical reflectors and when the light source remains
in the same position. However, the magnitude of the area 71 will
vary with the output of light source 27.
The particularly preferred reflecting surfaces illustrated in FIG.
6, and their orientation relative to one another and to plane 63
are defined with reference to a compass oriented as in FIG. 4 as
follows:
1. Parabolic surface 43 is closer to plane 63 than is elliptical
surface 45.
2. Parabolic surface 43 extends from 212.5.degree. to
287.5.degree..
3. Elliptical surface 45 extends from 44.degree. to 110.degree.,but
may be limited as to its outer rim at 90.degree..
4. The lower parabolic surface 47 extends from 192.5.degree. to
212.5.degree..
5. General reflecting surface 53 extends from 287.5.degree. to
307.5.degree..
6. General reflecting surface 54 extends from 307.5.degree. to
337.5.degree. .
7. Ventilation slot 57 extends from 337.5.degree. to 2.5.degree.
.
8. General reflecting surface 56 extends from 2.5.degree. to
44.degree. .
9. Flat reflecting surface 49 extends from 187.5.degree. to
192.5.degree. .
10. Flat reflecting surface 51 extends from 185.degree. to
187.5.degree. .
11. The axis 67 of parabolic surface 43 passes through F.sub.1 and
is in the range of 90.degree. to 135.degree. (90.degree. to
45.degree. from nadir), preferably 115.degree. to 120.degree.
(65.degree. to 60.degree. from nadir), and F.sub.1 coincides with
the focal point of parabolic surface 43.
12. The axis of parabolic reflecting surface 47 is about 2.degree.
to 10.degree. greater than the axis of parabolic reflecting surface
43.
13. The major axis F.sub.1 F.sub.2 of elliptical surface 45 is at
173.5.degree. (6.5.degree. from nadir).
14. The axis of parabolic surface 47 passes through the second
focal point F.sub.2 of elliptical surface 45.
A special benefit achieved by the reflector of FIG. 6 is the
provision of substantially absolute cutoff of direct lamp light
emanations at about 70.degree. from nadir without the use of an
auxiliary surface, such as surface 19 in FIG. 4, and without the
use of baffles or visors.
It will be evident from consideration of the embodiments of the
invention represented by FIGS. 4 and 6 that the invention provides
controlled asymmetric light distribution to produce substantially
constant illumination on a plane preferably encompassing the zone
within -10.degree. to +65.degree. from nadir, the extent of the
cutoff being controllable by the use of auxiliary reflectors or
baffles. In addition the invention provides means for reducing
glare in regions adjacent or in the zone of illumination. The
invention further provides sharp cutoff to the extent desired on
either side of nadir.
The reflecting surfaces of the invention may be constructed of any
suitable reflecting material, such as glass (coated or uncoated),
aluminum, stainless steel, and the like, whether in sheet, molded,
or cast form. While it is preferred to employ an elongated
substantially linear light source, the invention is operative with
substantially point sources of light or linear light sources.
Likewise, the reflecting surfaces may be parabolic or elliptical in
only one plane as illustrated, or may be surfaces of revolution, or
assemblies of the reflectors may be oriented to oppose each other
(with crossing of beams), or assemblies may be oriented
back-to-back or around a circle shining their beams outward. The
choice of dimension, plane or arrangement primarily depends on the
type of light source, expense of manufacture, and esthetic
considerations. The preferred embodiments employ surfaces which are
parabolic and elliptical in section, in conjunction with an
elongated light source such as a gaseous discharge lamp (e.g.,
mercury vapor, ceramic discharge, metal halide, fluorescent
sources, and the like), or a tungsten halogen lamp (e.g., quartz
iodine, and the like).
To the basic combinations of the reflecting surfaces of the
invention may be added visors, baffles and lenses of various types
in order to provide special effects. For example, it may be
desirable to close the reflector of the invention with a spread
lens in order to spread the illumination to the right and left of
the reflector as well as in a forward and downward direction.
It should be evident that the reflectors and luminaires of the
invention are economical in their construction and versatile in
their application and thus provide substantial improvements over
presently existing reflectors and luminaires.
The environments of use of the reflectors and luminaires of the
invention are virtually unlimited. Thus, they may be employed on
vertical supports to illumine roadways, pedestrian passages and
walks, parking lots, the exteriors and interiors of buildings, or
they may be placed on horizontal surfaces for the purpose of
illuminating vertical planes, as in the illumination of billboards,
interior walls, and the floodlighting of airport aprons, display
areas, and the like. In any of such positions, they may be turned
upward to illuminate ceilings, canopies, and the like.
With respect to the illumination provided by luminaires which
distribute light symmetrically, the relative candlepower curve
would indicate that there is candlepower "above" the line of
maximum candlepower (which line is 65.degree. above nadir in FIGS.
5 and 7). In other words, the curve would be approximately a mirror
image above the center of the beam as below the center of the beam.
It can be readily seen that, if such luminaires were used to obtain
substantially constant magnitude of illumination on a plane, with
the luminaire's maximum candlepower being aimed out toward the far
side of the illuminated area, there would be considerable spill
light (stray light) that would pass high above the area, which
spill light would cause discomfort glare and disability veiling
glare, or which would represent wasted light, or energy. The
reflectors and luminaires of the invention avoid these
problems.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
construction without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
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