U.S. patent number 3,700,883 [Application Number 05/074,563] was granted by the patent office on 1972-10-24 for faceted reflector for lighting unit.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Robert J. Donohue, Bernard W. Joseph.
United States Patent |
3,700,883 |
Donohue , et al. |
October 24, 1972 |
FACETED REFLECTOR FOR LIGHTING UNIT
Abstract
A reflector for a lighting unit includes a plurality of discrete
reflecting facets which are individually oriented with respect to a
light source such that the superposition of the reflected images
synthesizes a predetermined lighting pattern. The prescription for
making the reflector, by the techniques disclosed herein, involves
selecting the number, size, curvature, and location of each facet
to produce undistorted reflected images of the light source, the
cumulative effect of which produces the desired illumination
distribution within prescribed limits. Glare from the lighting unit
is substantially eliminated by positioning contiguous facets such
that uncontrolled reflecting surfaces are shaded from the light
source.
Inventors: |
Donohue; Robert J. (Birmingham,
MI), Joseph; Bernard W. (Berkley, MI) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
22120239 |
Appl.
No.: |
05/074,563 |
Filed: |
September 23, 1970 |
Current U.S.
Class: |
362/518;
362/348 |
Current CPC
Class: |
F21S
41/336 (20180101) |
Current International
Class: |
F21V
7/00 (20060101); F21v 007/09 () |
Field of
Search: |
;240/8.2,41.36,13R
;350/292,296,299 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Matthews; Samuel S.
Assistant Examiner: Braun; Fred L.
Claims
What is claimed is:
1. A reflector for projecting light from a source in a
predetermined illumination pattern, said reflector comprising: a
plurality of discrete reflecting facets; light focusing reflecting
surfaces on said reflecting facets, each of said reflecting
surfaces having curvatures individually focused with respect to the
source to project an undistorted image of the source, said
reflecting surfaces having reflecting areas projecting individual
images with a given horizontal and vertical image spread and
intensity, said reflecting surfaces further being spacially located
with respect to the source to direct said images toward select
portions of the desired illumination pattern such that the
superposition of said individual images synthesizes the pattern
within said prescribed limits, a portion of said reflecting
surfaces being in the form of right circular cylinders having
curvatures approximating parabolic cylinders which are focused with
respect to the source.
2. A faceted reflector for projecting light from a source in a
predetermined horizontal and vertical illumination pattern, said
reflector comprising: a plurality of discrete and contiguous
reflecting facets; light focusing reflecting surfaces on the facets
having uncontrolled light diffusing surfaces between contiguous
facets, said reflecting surfaces having reflecting areas for
projecting images with desired horizontal and vertical spreads and
projected intensities, said reflecting surfaces further being
focused with respect to the source for projecting glare free
undistorted images of the latter and being spacially located with
respect to the source to direct said undistorted images toward
select portions of said illumination pattern such that the
superposition of the projected undistorted images synthesizes the
pattern, the facets being further positioned with respect to
adjacent facets so as to shade said uncontrolled light diffusing
surfaces from said source thereby further reducing glare due to
scattered reflection.
3. A lighting unit having optics entirely on a reflecting surface
for distributing light in a desired illumination pattern,
comprising: an optically passive lens; a reflector, said lens and
said reflector having facing interior surfaces defining a lamp
envelope; a light source positioned in the envelope; a plurality of
facets on said reflector; cylindrical light focusing reflecting
surfaces on said facets, said reflecting surfaces being
interconnected by uncontrolled reflecting surfaces, said light
focusing reflecting surfaces having a shape and curvature for
intercepting illumination from the source and reflecting the latter
with a given image spread and intensity outwardly through said
optically passive lens toward select portions of said illumination
pattern, the position and shape of the individual facets being
interrelated so as to focus the facets with respect to the source
to project glare free undistorted images thereof and being
additionally positioned such that the image spreads and intensities
provide a composite pattern synthesizing said desired pattern, the
individual facets being further positioned relative to adjacent
facets and the light source so as to shade said uncontrolled
reflecting surfaces from the light source thereby reducing glare
from scattered illumination.
4. A motor vehicle lamp having optics placed entirely on a
reflecting surface for projecting a light beam in a desired
horizontal and vertical illumination pattern, comprising: a lens
having an optically passive light transmitting region; a reflector
adapted to be mounted on the motor vehicle and cooperating with the
lens to form a lamp envelope; a light source positioned within said
lamp envelope; a faceted surface on said reflector including
horizontal rows and vertical columns of discrete facets, said
faceted surface having sufficient area to project illumination of
requisite intensity throughout the contemplated pattern, said
facets being interconnected by uncontrolled glare producing
reflecting surfaces, said facets having right cylindrical
reflecting surfaces approximating parabolic cylinders focused with
respect to the source so as to project undistorted images through
said light transmitting region, each of said facets having a width,
height, and curvature and being positioned relative to the source
to distribute illumination with a given spread and intensity toward
a select portion of the desired illumination pattern, the facets
being interrelated so as to match the overall spread and intensity
of the illumination pattern within prescribed limits, the facets
being positioned relative to adjacent facets so as to shade said
glare producing reflecting surfaces from the light source thereby
reducing glare from uncontrolled reflection.
Description
The present invention relates to reflectors and, in particular, to
a reflector for a lighting unit such as a motor vehicle lamp
assembly.
Conventional motor vehicle lamps of the types used as headlamps,
cornering lamps, taillamps, and backup lamps normally include a
reflector and a lens defining a sealed lamp envelope in which a
coiled filament light source is positioned. The reflector is
provided with a suitably curved surface for collecting illumination
from the light source and redirecting the same outwardly onto the
lens. A light focusing optical system in the form of dioptic and
catadioptric rings, flutes, and prisms is normally provided on the
lens for horizontally and vertically distributing the illumination
outwardly from the lamp.
One of the primary factors affecting the quality of the projected
beam in these lighting units is the ability of the reflector to
intercept and direct toward the lens the light which is emitted
from the source. This capability of intercepting source
illumination, commonly designated the reflector light collection
efficiency, is defined as the fraction of total emitted light that
is intercepted by the reflector. The collection efficiency for a
given reflector is dependent on many structural characteristics of
the lamp such as reflector curvature, frontal area, and depth as
well as the location of the filament with respect to the reflector.
As a general statement, the efficiency is proportional to the total
solid angle subtended by the reflector surface as referenced to the
light source. Moreover, for a given reflector volume the efficiency
is dependent on the reflector shape or curvature which also
influences the quality of the projected beam. Thus, spherical
surfaces, while having an excellent light collecting efficiency,
provide little control over the reflected beam. Parabolic surfaces
provide slightly greater beam control but have a lower light
collecting efficiency than the spherical surfaces. Paraboloidal
surfaces, on the other hand, yield high collecting efficiencies and
directional beam control and, for this reason, have found the
greatest acceptance as reflecting surfaces for projected beam
lamps.
The optical performance for a paraboloidal reflector is, to a large
extent, determined by the position of the filament and the overall
size and focal length of the reflector. The efficiency as
calculated by conventional means, however, is merely an
approximation inasmuch as the filament normally has a finite length
and cannot be accurately located at the reflector focal point. For
this reason, the efficiency of a typical commercial lighting unit
may be considerably below the calculated value. Additionally, the
optical performance of a paraboloidal surface for a given focal
length and reflector depth is greatly influenced by frontal
configuration. By way of example, a right circular section will
produce the maximum collection efficiency with alterations of the
configuration, particularly from intentionally noncircular frontal
profiles, markedly reducing the reflector efficiency. While the
resultant loss can be partially recovered by increasing the
operating temperature and hence the illumination from the filament,
these required compensating manipulations present a definite
hindrance to the development of noncircular high performance
lamps.
The overall quality of the projected beam from the lamp assembly is
further affected by the optical characteristics of the lens used to
impart directional control to the reflected beam. More
specifically, the lens is typically comprised of numerous optical
bodies which refract the incident light to produce an undesirable
scattering or glare. Generally, this type of glare is associated
with the juncture between the adjacent optical bodies in the lamp
lens. The two edges produced during the lens manufacture have radii
which uncontrollably scatter illumination throughout the lens
thereby producing glare and, additionally, reducing the output
efficiency of the lamp assembly.
Accordingly, an object of the present invention is to provide a
reflector having a discretely faceted surface which produces a
projected beam of predetermined intensity distribution.
Another object of the present invention is to provide a reflector
having a flexible frontal configuration without an accompanying
impairment of optical performance.
Another object of the present invention is to provide a lamp
wherein the optics are placed entirely on the lamp reflector so as
to project a beam outwardly of the lamp in a desired illumination
pattern.
Yet another object of the present invention is to provide a method
of making a reflector having a predetermined frontal configuration
and depth which produces a desired projected light pattern.
A further object of the present invention is to provide a lamp
assembly wherein glare is significantly reduced by providing a
plurality of selectively oriented facets on the reflectors, the
junctures of which are shadowed from the light source to reduce
uncontrolled reflecting illumination.
Still another object of the present invention is to produce an
improved lighting unit having better pattern control and sharper
cut-offs by incorporating beam control entirely on a first optical
surface.
Generally, the above objects are accomplished by providing a
reflector of predetermined frontal area and depth with a plurality
of discrete reflecting facets. Each facet is individually oriented
with respect to the light source so as to project an undistorted
reflection of the latter in a prescribed direction. The
superposition of the individual reflections is then utilized to
produce a given illumination pattern. By combining a sufficient
number of reflector facets of the proper size, shape, and
orientation, a composite intensity contour can be synthesized
within prescribed limits. Such a reflector can incorporate a number
of geometrical surfaces. For example, paraboloidal sections,
circular cylinders, or parabolic cylinder, or a combination thereof
may be individually or collectively used to best synthesize the
desired pattern. After selection of the facet curvature necessary
to fulfill the desired optical prescription, the facets are arrayed
with respect to adjacent facets and the light source so as to
expose only one light diffusing structural radius to emitted light
thereby reducing glare due to uncontrolled reflection.
The aforementioned features and advantages of the present invention
will be apparent to one skilled in the art upon reading the
following detailed description, reference being made to the
accompanying drawings in which:
FIG. 1 is a front perspective view of a motor vehicle having a
lighting system including a cornering lamp made in accordance with
the present invention;
FIG. 2 is an enlarged view taken along line 2--2 of FIG. 1;
FIG. 3 is a view taken along line 3--3 of FIG. 2;
FIG. 4 is a two dimensional intensity contour of the illumination
pattern for the cornering lamp;
FIG. 5 is a three dimensional intensity contour of the illumination
pattern shown in FIG. 4;
FIG. 6 is a view taken along line 6--6 of FIG. 1;
FIG. 7 is a schematic view illustrating horizontal image spread of
a facet reflecting surface;
FIG. 8 is a schematic view illustrating vertical image spread of a
facet reflecting surface;
FIG. 9 is a schematic view illustrating the circular approximation
of a parabolic surface;
FIG. 10 is a schematic view illustrating selective angular
positioning of the facet reflecting surfaces;
FIG. 11 is a horizontal schematic view illustrating initial angular
positioning of the facets;
FIG. 12 is a view similar to FIG. 11 illustrating shadowing of
uncontrolled reflecting surfaces;
FIG. 13 is a schematic view illustrating one method of facet
rotation;
FIG. 14 is a view similar to FIG. 13 illustrating an alternate
method of facet rotation;
FIG. 15 is a view illustrating the glare from a faceted
reflector;
FIG. 16 is a view illustrating the glare from a lens;
FIG. 17 is a view illustrating the effect of the facet angle on the
focal length position;
FIG. 18 is a top view of a facet die segment;
FIG. 19 is the side view of the die segment of FIG. 18; and
FIG. 20 is the front view of the die segment of FIG. 18.
Referring to FIG. 1, there is shown a motor vehicle 10 having a
lighting system including headlamps 12, combination turn signal and
parking lamps 14, and cornering lamps 16. All of the lamps are
symmetrically disposed on opposite sides of a longitudinal vehicle
axis 18. Each of the aforementioned lamps is designed to project
the illumination outwardly of the vehicle into a predetermined
illumination pattern as prescribed by applicable standards. Thus,
the headlamps 12 are used as a major lighting device to provide
general illumination ahead of the vehicle during driving conditions
of reduced visibility. The turn signal lamps 14 flash in unison
with corresponding rear lamps to indicate the intention of the
vehicle to change direction toward the side on which the signal
lamp is flashing. The parking lamps 14 on both sides of the vehicle
are simultaneously steadily energized to indicate the overall width
and length of the motor vehicle. The cornering lamps 16 are
selectively steadily burning lamps used in conjunction with the
turn signal system to supplement the head lamps 12 by providing
additional illumination in the direction of a contemplated
turn.
Referring to FIGS. 2, 3, and 6, the cornering lamps 16 are mounted
in an opening 20 formed in the side of the vehicle at the lower
forward portion of the vehicle front fender 22. Each lamp 16
generally comprises a reflector 24, a light source 26 carried by
the reflector 24, and a lens 28, the outer periphery of which is
bounded by the edge of the opening 20. The reflector 24 includes a
peripheral groove 30 which retains a resilient gasket 32. The lens
28 includes a rearwardly projecting marginal lip 34 that engages
the gasket 32 to form a sealed envelope 36 defined by the interior
surfaces of the lens 28 and the reflector 24.
The lens 28 includes a marginal flange 38 on which a second
resilient gasket 40 is positioned. The cornering lamp 16 is
positioned at the opening 20 with an inwardly turned edge of the
latter resiliently engaging the gasket 40. The cornering lamp 16 is
then fixedly secured in this position by fasteners 42 which clamp
outwardly projecting mounting ears 44 at the sides of the reflector
24 to spaced brackets 46 fixed to the interior surface of the front
fender 22.
The lens 28 is formed of a light transmissive material such as
plastic and has a clear front window 48. When used with the subject
faceted reflector, the lens 28 may be optically passive and require
none of corrective optical means conventionally used on lamp
lenses. However, the window 48 may include optical flutes or prisms
for additionally distributing the illumination controlled by the
reflector 24, if the same are deemed desirable.
The light source 26 is horizontally and vertically centered with
respect to the reflector 24 and generally includes a socket 50 and
a lamp 52 having a helically coiled filament 54. The socket 50
includes a pair of leads 56 which are electrically connected to a
power supply (not shown) such as the vehicle battery for energizing
the filament 54. While the light source 26 may take various forms
depending on the type of lighting unit in which it is incorporated,
appropriate means should be provided for accurately locating the
filament 54, in assembly, with respect to the hereinafter described
faceted surface of the reflector 24.
The reflector 24 includes a dish-shaped base section 58 having a
front faceted surface, generally indicated by reference numeral 60,
which is suitably coated or otherwise prepared to intercept and
reflect light emitted from the filament 54. More specifically, the
faceted surface 60 may be aluminized, silvered, or metallically
coated as by chrome deposition to provide the aforementioned
reflecting capabilities.
The faceted surface 60 is defined by a plurality of individually
oriented discrete facets which will be, for purposes of
description, hereinafter designated by subscripts depending on
their position with respect to the filament 54. Thus, as shown in
FIG. 3, the faceted surface 60 is horizontally divided into three
rows, a middle row bearing the subscript M, an upper row bearing
the subscript U, and a lower row bearing subscript D. The faceted
surface 60 is vertically divided into seven columns, the middle
column being designated 1 with adjacent rows on the left being
successively designated as 2L, 3L, and 4L and adjacent rows on the
right being successively designated as 2R, 3R, and 4R. By way of
example, the middle row successively contains the following facets:
4LM, 3LM, 2LM, 1M, 2RM, 3RM, and 4RM. Each of the aforementioned
facets is positioned within the envelope 36 with respect to the
filament 54 such that their cumulative effect is to horizontally
and vertically distribute emitted light from the source 26 in a
predetermined illumination pattern.
More specifically, all facets are deliberately positioned behind
the light source 26 so as to reflect an image of the filament 54.
In this manner, the illumination pattern produced by the complete
reflector is the sum or superposition of all the individual images.
The particular contribution of the individual facet is determined
by its projected pattern which has characteristics dependent on its
shape and location with respect to the light source 26. By
combining facets in a sufficient number of the proper size, shape,
and orientation, the contemplated illumination pattern can be
accurately synthesized.
Experience, in this respect, has indicated that the intensity
pattern for a cornering lamp should provide a wide illumination
pattern in a horizontal plane and a relatively narrow or
concentrated pattern in a vertical plane. Accordingly, to most
conveniently accomplish this result, the major axis 70 of the lamp
16 is horizontally disposed at a suitable angle to the longitudinal
vehicle axis 18 and the minor axis 72 is vertical and mutually
perpendicular to the major axis 70 and vehicle axis 18.
The intensity or isocandle contour for the cornering lamp 16
positioned on the right side of the vehicle is shown in FIGS. 4 and
5 wherein a high or peak intensity zone 80 is established slightly
below the major axis 70 of the lamp and angularly displaced with
respect to the longitudinal vehicle axis 18. The high intensity
zone 80 is circumscribed by zones of decreasing intensity,
designated successively 82, 84, 86, and 88. For purposes of future
reference, the nine hundred candlepower (cp) peak intensity zone 80
positioned at 35.degree. from the longitudinal vehicle axis 18 and
1.5.degree. below the lamp major axis 70. The lamp 16, as
referenced to the vehicle longitudinal axis 18, has a reflector
axis 120 angularly displaced 45.degree. outwardly and 2.5.degree.
downwardly. The center of the overall intensity pattern is
determined by the 0 to 100 cp slice pattern which has a relatively
narrow vertical spread V and relatively large horizontal spread H.
More particularly, in the preferred embodiment, the horizontal
spread H is approximately 50.degree. and subtends the sector from
20.degree. to 70.degree.. The vertical spread V is approximately
5.degree. and extends downwardly 5.degree. from the horizontal lamp
major axis 70.
The cornering lamp 16, as previously mentioned, includes a
plurality of individually oriented facets which accurately
synthesize the above-described illumination pattern within
prescribed limits. The exact size, curvature, and orientation of
the individual facets is determined by a number of design
requirements, foremost of which are the resultant light pattern;
the peripheral configuration of the reflector; the depth into which
the reflector must fit; the filament configuration; the position of
the filament with respect to the reflector; and the temperature
profile of the filament.
With the wide horizontal and narrow vertical spreads required in
cornering lamps, a filament positioned with its longitudinal axis
in a horizontal plane in combination with reflector facets which
are parabolic or circular cylinders having axes parallel to the
horizontal plane has been found to provide the most satisfactory
results.
The peripheral configuration and depth of the reflector is normally
determined in advance by styling and other design configurations.
As such, the basic size of the lamp reflector will be subjectively
influenced by aesthetics, the required intensity profile, and the
practical limits of reflector efficiency and focal length. Inasmuch
as lamps with a collection efficiency of less than 30 percent
provide unacceptably low performance, this figure will specify a
reflector height once the width and focal length of the reflector
are given. The width is usually prescribed by the styling
aesthetics insofar as the same is compatible with the practical
performance limits.
Regardless of the many considerations noted above, the hereinafter
described method of synthesizing a desired illumination pattern
restricts the actual reflector size only to the extent that the
required precision of the final pattern necessarily controls the
number of facets and their accompanying reflector area. The
reflector form also, to a large extent, determines the location of
the filament and generally establishes the size of the central
facet which constitutes the basic building block in determining the
boundaries of the desired illumination pattern. The focal length of
this central facet will hereinafter be regarded as the focal length
of the reflector.
Other criteria for effecting initial design of the reflector are
the filament candlepower required to supply the energy for the
illumination pattern and the practicability of placing the filament
at the focal point of the reflecting surface. Generally, this last
criterion establishes a minimum focal length of about one inch for
motor vehicle lamps. Insofar as the filament energy output is
concerned, the operating temperature and lifetime requirements of
tungsten filaments require a cylindrical helically wound
configuration which satisfies the specified candlepower
requirements.
Once the focal length is set, the depth is determined from the
buildup of the facets. In this respect, the depth can be
approximated by computing the depth for a paraboloid of a given
frontal area having the same focal length as the faceted reflector.
Alternately, the depth can be specified within the limits and the
facets designed to fit within the thus prescribed frontal area and
depth. This last method of building up the pattern is the most
confining, of course, and may produce the least desirable fit of
the desired pattern.
The exact number of facets chosen for a given reflector depends
upon the permissible size of the reflector, the shape of the
desired intensity pattern, and the precision to which the pattern
must be fitted. The size of the facets, in turn, is determined by
the size of the desired intensity pattern. The shape and
orientation of the facets are primarily controlled by the relative
position of the various intensity zones within the overall
illumination pattern.
Regarding the optical characteristics of the facets, as shown in
FIGS. 7 and 8, a representative facet 100 having a parabolic
cylindrical reflecting surface 102 will distribute light from a
filament 104 through a horizontal image spread X. The magnitude of
the spread X will be conventionally optically determined by the
width of the facet 100, the distance between the filament 104 and
the reflecting surface 102, as well as the overall length and
configuration of the filament 104. The reflecting surface 102 will
produce vertical image spread Y, the value of which is determined
by the subtended angle .phi. of the surface 102 with respect to
filament 104, the distance between the reflecting surface 102 and
the filament 104, the curvature of the reflecting surface 102, and
the diameter of the filament 104. The same relationships generally
hold true for the other contemplated reflecting surfaces such as
paraboloidal, spherical, cylindrical, or elliptical.
With the above guidelines, the optical prescription for the lamp 16
proceeds by dividing the idealized illumination pattern in constant
intensity regions, as shown in FIGS. 4 and 5, and thereafter
matching the shape and intensity of the images from the several
facets with specific regions of the pattern following two criteria
insofar as the shape of each individual facet pattern is concerned.
First, the total spread of the image with an individual facet
should not exceed either horizontal spread H or the vertical spread
V of the desired resultant pattern. Second, the illumination from
each facet must be directed toward an appropriate position in the
resultant pattern.
In particular, the prescription for the subject cornering lamp
pattern is established by initially prescribing the central column
of facets 1M, 1U, and 1D. Inasmuch as this central column is
virtually unrestrained insofar as width and orientation are
concerned and need only satisfy the first-mentioned criteria, their
facets are, for convenience, provided with cylindrical reflecting
surfaces having axes parallel to the axis of the filament 54. The
central facet 1M represents the basic facet in the synthesis of the
reflector and is selected to produce an image as wide and as high
as the lowest considered intensity zone. In the present instance,
this zone is the 100 cp. slice of the resultant beam and is
approximately 50.degree. by 5.degree.. The sizing and placement of
this facet is most easily fulfilled by using a circular cylinder
having its focal length coaxial with the filament 54. As shown in
FIG. 11, the perpendicular bisector of the center or primary facet
1M is colinear with the actual lamp axis 120. This orientation
directs the illumination toward the geometrical center of the
intensity pattern, 45.degree. horizontal and 2.5.degree. down
vertical (FIG. 5).
With the width and height of the basic facet thus determined, the
sizes of the upper and lower facets, 1U and 1D, are established.
For convenience of manufacture, the width of these facets is
selected to be the same as the width of the basic facet 1M.
However, the height of these facets will generally be less than the
height of the center facet. Accordingly, the facets will produce an
image as wide as the 100 cp. pattern but with a considerably
narrower vertical band.
Because of the ability of the parabola to project a confined beam
the facets 1U and 1D are most suitably parabolic cylinders having
the filament 54 at their respective focal lengths. However, in
order to simplify construction, inasmuch as a parabolic cylindrical
surface is considerably more difficult to manufacture than the
circular cylindrical surface, the present invention uses a circular
approximation of these surfaces. By way of example, the radius of
an approximating circular surface can be represented in the
following manner taken with reference to FIG. 9 wherein a parabolic
surface 122 having a focal length P is approximated by a circular
surface 124 having radius R and a center C at (Yo, Zo) according to
the formulas:
Yo = -YZ/P
Zo = 3Z + 2P
R = [(Y - Yo).sup.2 + (Z - Zo).sup.2].sup.one-half
The shape of the circle thus generated matches the parabola at the
point (Y,Z) 126 which is taken at the vertical midpoint, (Y.sub.1 +
Y.sub.2)/2 of the surface. Of course, the degree of approximation
diminishes as the distance from point 126 increases. Therefore, the
focal point 132 and center of curvature of the circular cylinders
are not necessarily in the plane of the filament 54 which is still
located at the focal length P of the original parabolic surface
122.
The remaining vertical height of the reflector in the center column
is evenly divided between the upper and lower facets 1U and 1D. The
images of these facets are directed toward the most intense
vertical region, 2.5.degree. down, of the pattern with the center
of the facet image centered on the axis 120. The center column of
facets thus establishes the lowest intensity region of the desired
pattern and partially contributes to the remaining regions.
Thereafter, buildup of the reflector proceeds outwardly from the
vertical edges of the center column facets.
The length and height of each facet in the M or middle horizontal
row is governed by the length and height of that intensity slice of
the total pattern which the facet image is attempting to match. For
example, the constant intensity slice 300 cp., FIG. 4, has a
horizontal spread of about 40.degree. and a vertical spread of
approximately 4.degree. with a and centers at 40.degree.
horizontal. Thus, as shown in FIG. 11, the 2M facets are directed
toward 40.degree. horizontal with sufficient width for a 40.degree.
horizontal spread.
For the initial synthesis, the vertical edges of adjacent facets
should be continuous in order to most efficiently utilize the
predetermined reflector volume to best initially synthesize the
desired pattern. The remaining middle facets are directed toward
the peak intensity region of the total pattern 35.degree.
horizontal (FIG. 11). Representatively, as shown in FIG. 10, these
two requirements orient the 2LM facet or surface 150 at an angle
.theta..sub.2L with respect to the basic facet 1M or line 152 with
the facets being commonly joined at vertical edge 154. Insofar as
the middle row of facets is concerned, the angle is referred to the
plane of the basic facet 1M at the horizontal center line of the
lamp. The angle .theta..sub.x for each facet is determined by
solution of the following equation:
tan (2.theta..sub.x +.psi.) = (a + L)/(P - L tan .theta..sub.x)
where
.psi. is the angle between the reflected light ray 156 and the
reflector axis 120;
a is the distance from the reflector axis 120 to the edge 154;
P is the distance along the axis 120 from the filament 54 to the
edge line 152, and
L is the distance between the center of the facet 2LM and the edge
154.
For each of these facets, the radius of curvature, r.sub.cf, is
equal to twice the distance between the line 152 which comprises
the cylindrical surface in the horizontal plane and a second line
158 through the center of the filament 54 parallel to and in the
same plane as the first line, or r.sub.cf = 2P for facet 1M.
Referring to FIG. 11, the 4RM facet includes a line 160 comprising
the cylindrical surface of the facet in the central horizontal
plane. A second line 162 passes through the center 164 of the
filament 54 and is parallel to and lies in the same plane as line
160. This spacing establishes a "D-value" or distance D.sub.4R
between the lines 160 and 162 which is one-half the radius of
curvature, r.sub.cf, of the facet 4RM. The "D-values" for the
remaining facets in the middle row M are established in a similar
manner. For the upper rows U and lower rows D, the facets are
circular cylinders which approximate parabolic cylinders in the
above-described manner. The focal length P of the initially
parabolic cylinder is the "D-value" of the middle facet in the
corresponding column. However, as previously mentioned, when the
parabolic cylinder is established, the focal point and the center
of curvature of the resulting circular cylinders are not
necessarily in the horizontal plane.
The upper or lower facets in a given column are, to a large extent,
dependent on the size and position of the middle facet. More
specifically, in as much as both the middle row of facets and the
total lamp height are symmetrical about the horizontal lamp axis,
the height of the upper facets, for instance, is the distance
between the upper edge of facet 2RM and the upper vertical edge of
the reflector. The width and angle .theta..sub.x with respect to
the axis of the filament 54 is the same as for the middle facet to
minimize boundary gaps. This process is applicable to all the rows
and columns of facets to complete initial synthesization of the
desired pattern. The pattern thus prescribed, in many instances,
provides an acceptable optical performance for the reflector.
However, further precision and refinement of the basic reflector
surface can be achieved by selectively reorienting the separate
facets.
While many repositioning techniques can be used to improve the
optical performance of the reflector, the two methods described
below significantly improve the illumination pattern while
minimizing the required facet movement. In one method, as shown in
FIG. 14, a representative facet 170 as referenced at the
geometrical center of the reflecting surface 172 is universally
rotated about the focal axis 174. Alternately, the facet 170 is
rotated about a horizontal axis 176 passing through the center 177
of its reflecting surface 178 to produce a vertical shift of the
image and about a vertical axis 179 passing through the center 177
to produce horizontal shift of the image. Inasmuch as the latter
method generally requires a lesser repositioning of the individual
facets to achieve a given improvement in the overall illumination
pattern, this method will be hereinafter described.
The aforementioned rotation of the element 170 about its
geometrical center causes the focal length of the surface to
retreat from a line through the center of the filament 54 thereby
distorting the reflected image of the latter. With each incremental
shift, the image projected by the reflecting surface will become
increasingly distorted. Thus, at some predetermined point, which we
have determined to be about 4 percent of the focal length, an
unacceptably distorted image will be produced. Therefore, if the
shift of the image is greater than this value, a revised facet
angle ".theta." and a new radius of curvature r.sub.cf for the
facet must be established so that the reflected image is once again
within prescribed limits of distortion and directed toward the
intended position in the illumination pattern.
For example, as shown in FIG. 17, a facet 180 has an original facet
angle .theta..sub.2R with respect to the axis 182 of the filament
54 and a "D-value," D.sub.2R, as established between a line 184
through the center of the filament 54 and a parallel line along the
reflecting facet 180. As the surface 180 is rotated about its
center 188 through an angle .OMEGA., to a rotated position 190, the
line 192 parallel to the surface 190 placed at the original
"D-value" is shifted an incremental distance d from the center of
the filament 54. To compensate for this displacement, the radius of
curvature of the facet is appropriately changed to establish a
revised facet "D-value," D'.sub.2R. By way of example, if the
original radius and the facet angle .theta. for the 2RM facet are
3.065 in. and 54.degree. 40', and the image is to be shifted
10.degree. toward the car axis in the horizontal plane, the facet
is rotated 5.degree. about the center of its surface to effect this
required shift. However, this movement causes a 0.100 in. inward
shift of the facet focal length thereby producing a distorted
image. This movement exceeds the aforementioned 4 percent for an
undistorted image inasmuch as:
shift/focal length = 0.100/1.5 = 6.7%
This 10.degree. image shift can be accomplished while maintaining
the filament on focus by recomputing the facet prescription to a
radius of 3.268 and a facet angle of 61.degree. 32'.
By either of the above rotational methods, the marginal edges
retreat or advance with respect to the edges of adjacent facets.
Referring to FIG. 12, the boundary discontinuities between adjacent
facets shown in solid lines produces uncontrolled reflecting
surfaces 206 and shadowed reflecting surfaces 208. The surfaces 206
are exposed to the the filament 54 and because they have
indiscriminate shapes and positions, scatter the intercepted light
thereby causing glare. On the other hand, the surfaces 208 are not
exposed to the light and, accordingly, do not present a glare
problem.
For the molded lamp components, a minimum draft angle must be
provided at the juncture between the facets in order to permit the
release of the article from the mold. A conventional lens, as shown
in FIG. 16, having optical flutes 209 or the like formed on an
interior surface produces uncontrolled surfaces 210 between exposed
edges 212 and 214 produced by the draft angle.psi..sub.L. At each
of these edges, the light will be uncontrollably reflected and
refracted. However, for the facet reflector shown in FIG. 15, the
required draft angle .psi..sub.R produces releasable, conical
surfaces 220 and permits location of adjacent facets such that only
one edge 222 is exposed to the light from the filament. The other
radius 224 is hidden from the filament and, therefore, does not
contribute to glare.
Referring to FIG. 12, for an arbitrary diepull angle Z between
reflector and the lamp axis 120 and the pull line 230, the
uncontrolled surfaces 206 are not deliberately positioned with
respect to the filament and thus randomly distribute or scatter
illumination. The glare caused by such surfaces is obviated in the
present invention by shifting the outward facets rearwardly along
the line parallel to the pull line 230 until the juncture surface
is hidden or shaded from the filament. The facet angle .theta. is
then recalculated to redirect an undistorted image toward the
intended position in the intensity pattern.
When the above operations have been completed, the same is
translated into numerical form for construction of a die from which
the desired reflectors can be manufactured by conventional forming
processes. Each facet, as shown in FIGS. 18 through 20, will be
produced by a die segment 240 having a reflecting surface 242 with
a profile width A and a profile height B. The reflecting surface
242 will have a radius R with origin axis 244 displaced a distance
Q from the center axis 246 of the segment 240. The surface normal
247 between the reflecting surface 242 and the axis 246 is inclined
at an angle .alpha.. The center of the reflecting surface 242 will
be displaced a distance I from rear face 250 of the segment 240.
The axis 244 is then displaced a distance Z in the horizontal plane
as measured from a reference pin 252 aligned with the axis 246 and
having a 0.250 in. diameter. As designated in the aforementioned
manner, a lamp assembly having a frontal profile of 2.50 in.
.times. 5.00 in. and a central facet focal length of 1 inch was
successfully manufactured to produce a resultant light pattern as
shown in FIGS. 4 and 5 using the following dimensions.
facet A B Sin.alpha. Z R Q
__________________________________________________________________________
1M 0.625 1.250 0.0218 3.250 2.000 0.021 Right 1U 1.625 0.625
-0.1062 3.903 2.694 1.138 Left 1D 0.625 0.625 0.1062 3.901 2.694
1.144 Right 2LM 0.688 1.000 -0.2712 3.413 2.097 0.019 Right 2LU
0.688 0.750 -0.3720 3.903 2.666 1.040 Left 2LD 0.688 0.750 0.3788
3.920 2.666 0.988 Right 2RM 0.688 1.000 0.2506 3.378 2.090 0.015
Left 2RU 0.688 0.750 0.2197 3.942 2.663 1.020 Right 2Rd 0.688 0.750
-0.2346 3.939 2.663 1.015 Left 2LM 0.750 1.000 -0.6155 3.839 2.440
0.019 Right 3LU 0.750 0.750 -0.6473 4.260 2.925 0.983 Left 3LD
0.750 0.750 0.6481 4.269 2.925 0.054 Right 3RM 0.750 1.000 0.36574
3.748 2.296 0.034 Right 3RU 0.750 0.750 0.3746 4.362 2.901 1.048
Right 3RD 0.750 0.750 -0.3926 4.359 2.901 1.020 Left 4LM 0.750
1.000 -0.8161 4.556 3.065 0.047 Right 4LU 0.750 0.750 -0.8189 4.919
3.447 0.983 Left 0.750 0.750 0.8179 4.946 2.447 0.900 Right 4RM
0.750 1.000 0.5033 4.374 2.706 0.019 Left 4RU 0.750 0.750 0.5253
4.785 3.130 0.923 Right 4RD 0.750 0.750 -0.5249 4.769 3.130 0.973
Left
__________________________________________________________________________
The instruction left or right in the last column of the table
refers to the direction of the center of the radius 244 from the
facet centerline 246 (distance Q) as viewed in FIG. 19.
Although only one form of this invention has been shown and
described, other forms will be readily apparent to those skilled in
the art. Therefore, it is not intended to limit the scope of this
invention by the embodiment selected for the purpose of this
disclosure but only by the claims which follow.
* * * * *