Note: Descriptions are shown in the official language in which they were submitted.
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METaL HALIDE LaNP EaVING VACUU~ SHROUD
FOR IMPROVED PERFORNANCE
CROSæ REFERENCE TO RELATED AP~ICATION8
U.S. Patent No. 4,868,458 issued September 19,
1989 and Canadian Patent Application Serial No. 589,943,
filed February 2, 1~89 respectively for "Xenon Lamp
Particularly Suited For Automotive Applications" of
Davenport and Hansler and "Xenon-Metal Halide Lamp
Particularly Suited For Automotive applications" of
Bergman, Davenport, and Hansler, all assigned to the same
assignee as the present invention, are all related to the
present invention.
BACRGROUND OF THE INVENTION
The present invention relates to a discharge
lamp especially suited for forward lighting application
of a vehicle such as an automobile, truck, bus, van or
tractor. More particularly, the discharge lamp is a
matal halide type which is particularly suited for a
vehicle such as an automotive and has means for reducing
the typically expected losses occurring during the
operation of a metal halide lamp.
Automotive designers are interested in lowering
the hood line of cars in order to improve their
appearance and also their aerodynamic performance. As
discussed in the cross-referenced U.S. Patent No.
~g
`--` 1309~2
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4,868,458, the amount that the hood lines may be lowered
is limited by the dimensions of the automotive headlamp,
which, in turn, is limited by the dimensions of the light
source which is typically comprised of a tungsten
filament.
Cross-referenced U.S. Patent No. 4,868,458 and
Canadian Patent ~pplication Serial No. 589,943
respectively disclose a xenon lamp and a xenon-metal
halide discharge lamp having dimensions which are
substantially reduced relative to a tungsten light source,
which, in turn, allow for the reduction of the overall
size of the reflector of the automotive headlamp housing a
light source so that the hood line of the automobile may
be substantially reduced by the automotive designers. In
lS addition to the xenon lamp and xenon-metal halide lamps,
it is desired to provide a metal halide lamp for
automotive applications so as to allow for aerodynamic
styling of automobiles. Further, it is desired to provide
for a xenon-metal halide lamp having improvements related
to automotive and other applications. Still further, in
addition to the metal halide light source serving the
needs of automobile, it is desired that an improved metal
halide light source find lighting applications in the
home, office and other commercial and industrial usages.
2S In one lighting application particularly
suited for automobiles, it is desired to provide a
metal halide lamp that may be operated from a low
frequency alternating current (A.C.) power source or
direct current (D.C.) power source. In such A.C. and
D.C. applications, the metal halide lamp typically
experiences the effects of catephoresis which cause the
halides of the metal halide lamp to be moved or swept
into the end regions of the lamp so as not to
contribute to providing the desired illumination of
such lamp. It is desired that means be provided which
~. ~
1303~2
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substantially reduce or even eliminate the detrimental
effect of catephoresis on the operation of the metal
halide lamp.
A second disadvantage typically related to metal
halide lamps, particularly metal halide lamps having
relatively small dimensions so as to be adapted to
automotive applications, is that these lamps typically
include a sodium iodide as a part of their fill, and
the sodium ions of this ingredient may migrate by
electrolysis through the fused silica of the metal
halide lamp during operation. As the sodium is lost
and the free iodine of the sodium iodide is left behind
in the lamp, the lamp illumination deteriorates through
the loss of sodium radiation. The free iodine causes
the operating voltage of such lamp to begin to rise
which may ultimately cause the metal halide lamp to
experience a failure. It is desired that means be
provided to substantially reduce or eliminate the
sodium ion migration problem typically associated with
the operation of metal halide lamps.
A third disadvantage related to metal halide lamps,
is concerned with the structure necessary for mounting
the metal halide light source within an outer envelope
so as to form the overall lamp. The structure, in
particular a metal structure, when subjected to
incident radiation emitted from the metal halide light
source commonly causes the metal structural members to
emit photoelectrons. Some of these photoelectrons
drift to the outer surface of the metal halide light
source, charging such a surface in a negative direction
and accelerating the electrolysis of the sodium ions
through the fused silica of the metal halide lamp. It
is desired to minimize or reduce the metal structural
members for mounting the metal halide light within its
related lamp so as to correspondingly reduce the
electrolysis of the sodium ions through the fused
1309~2
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silica created by metal ~tructural members which emit
photoelectrons.
A further disadvantage related to metal halide
lamps, is the disadvantageous feature created by the
presence of hydrogen and water which may dif~use out of
the metal halide lamp. It is desired that means be
provided to reduce the detrimental effects of hydrogen
and water without contributing to any further
disadvantageous operation of the metal halide lamp such
as the creation of photoelectrons that would otherwise
cause the loss of the sodium ion from the metal halide
lamp.
A still further disadvantage that may possibly
occur with a halide lamp is related to the rupturing of
the metal halide lamp that is typically operated at a
relatively high pressure. Upon the limited possibility
of such an occurrence, the high pressure within the
metal halide lamp may cause the material of such a
metal halide lamp to be dislodged at a relatively high
velocity which may possibly fracture the outer envelope
in which the metal halide lamp is housed. It is
desired that confinement means be provided so as to
reduce the possible effects of the rupturing of such a
metal halide lamp operated at a relatively high
pressure.
Accordingly, it is an object of the present
invention to provide a metal halide lamp having means
so as to reduce the detrimental effects of catephoresis
typically created by low frequency A.C. operation or
D.C. operation of such a lamp.
It is a further object of the present invention to
provide ~eans to reduce the sodium ion migration
typically experienced for a metal halide lamp.
It is a further object of the present invention to
reduce the sodium ion migration caused by metallic
mounting members emitting photoelectrons which
1309~2
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contribute to the loss of the ~odium ions of the metal
halida lamp.
It is still a further ob~ect of the present
invention to provide containment means BO as to reduce
the possible detr~mental effects that may occur during
the unlikely event of the rupturing of the metal halide
lamp operated at a relatively high pressure.
SUMMARY OF THE INVENTION
The present invention is directed to a metal halide
light source having physical dimensions and operational
characteristics finding various applications and which
is particularly suited to serve as a light source for
an automotive headlamp.
The metal halide light source comprises an inner
envelope and a shroud member merged with the inner
envelope. The inner envelope contains mercury along
with a metal halide compound and may contain a xenon
gas. The inner envelope has a pair of electrodes
disposed therein and separated from each other by a
predetermined distance. The electrodes have means for
connecting to inleads which extend out of the inner
envelope. The shroud member is merged with the inner
envelope and separated from the side walls of the inner
envelope by a predetermined distance to provide a
chamber between the inner envelope and the shroud.
In one embodiment of the present invention the
light source is used for an automotive headlamp which
comprises a reflector having a predetermined focal
length and focal point along with a section to which is
mated means capable of being connected to an external
source of the automobile. A lens is mated to the front
section of the reflector and the light source is
predeterminantly positioned within the reflector so as
to be approximately disposed near the focal length of
the reflector.
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13094~2
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side view generally illu~trating an
automotive headlamp in accordance with the present
invention having its light source ori0ntated in a
vertical manner.
Fig. 2 is a top view generally illustrating an
automotive headlamp in accordance with the present
invention having its light source oriented in a
horizontal axial manner.
Fig. 3 illustrates the metal halide light source in
accordance with the present invention having an inner
envelope and a shroud member merged with the inner
envelope.
Figs. 4 and 5 illustrate alternate embodiments of
an inner envelope merged with a shroud member.
Figs. 6(A) and 6(B) respectively illustrate a
comparison between the beam divergence of an automotive
headlamp system using an incandescent light source and
the metal halide light source of the present invention
in reflectors of the same size.
Figs. 7(A) and 7(B) comparatively illustrate the
size of the reflector needed for the use of an
incandescent light source and the metal halide light
source of the present invention in order to have the
same light beam divergence.
Figs. 8(A) and 8(B) are respective perspective
views of a prior art rectangular automotive headlamp
and a rectangular automotive headlamp in accordance
with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 is a side view generally illustrating an
automotive headlamp 10 in accordance with one
embodiment of the present invention. The automotive
headlamp 10 comprises a reflector 12, a lens member 14
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and a metal halide light source 16.
The reflector 12 has a rear section 18 having means
mounted thereon such as a connector 20 with prongs 22
and 24 capable of being connected to an external source
of an automobile. The reflector 12 has a predetermined
focal length 26 measured along the axis 28 of the
automotive headlamp 10 and located at about the
mid-portion of the light source 16. The light source
16 is predeterminedly positioned within the reflector
12 so as to be approximately disposed near the focal
length 26 of the reflector. For the embodiment
illustrated in Fig. 1, the light source 16 is oriented
in a vartical and transverse manner relative to along
the axis 28 of the reflector 12, whereas, Fig. 2
illustrates the light source 16 as being oriented in a
horizontal manner relative to and along the axis 28 of
the reflector 12.
The reflector 12 that cooperates with the light
source 16 has a parabolic shape with a focal length in
the range of about 6mm to about 35mm with a preferred
range of about 8mm to about 20mm. The lens 14 is mated
to the front section of the reflector 12. The lens 14
is of a transparent material selected from the group
consisting of glass and plastic. The transparent
member has a face preferably formed of prism members.
The light source 16 has a pair of electrodes 30 and
32 disposed at opposite ends thereof at its neck
portions and separated from each other by a
predetermined distance in the range of about 2mm to
about lOmm. The light source 16 is connected to the
rear section of the reflector 12 by means of relatively
heavy inleads 34 and 36 each having one end
respectively connected to electrodes 30 and 32 by
respective inleads 38 and 40 and their other end
respectively connected to prongs 22 and 24. The
electrodes 30 and 32 are of a rod-like member formed of
1~09452
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a material preferably selected from the group o~;Jc
comprising tungsten and tungsten with 1-3% thorium.
Further the electrodes 30 and 32 are respectively
connecting to the foil members 42 and 44 soaled in the
neck portions for one embodiment of the pr~sent
invention applicable to a quartz light source 16. Each
of the foil members 42 and 44 are electrically
connected to their respective inleads 38 and 40. For
another embodiment related to light source 16
preferably of a t,vpe #180 glass available from the
General Electric Company, the electrodes 30 and 32 may
be a rod-like members preferably welded to molybdenum
inleads which may be directly sealed in the #180 glass,
thereby eliminating the need of foil members 42 and 44.
The light source 16, shown in detail in Fig. 3, for
one embodiment of the present invention, is comprised
of a inner envelope 46 and a shroud member 48 which is
integrated or merged with the inner envelope at a
portion of each of the neck sections of the inner
envelope so as to form one integral member.
As will be discussed hereinafter, one of the main
advantages of the light source 16 having a vacuum
shroud 48 is to produce an improved wall temperature
over prior art devices by eliminating the cooling
effects of gas conduction and convection. This
improved uniform temperature results in more metal
halide being vaporized and maintained in the discharge
of the arc condition within light source 16 which
improves the efficiency and color of the light source
16. This improved uniform temperature also makes the
light source less dependent on its orientation within a
housing such as within the automotive lamp 10. The
vacuum shroud 48 also reduces the typically occurring
catephoresis effects during D.C. and low frequency
3S operating of the light source 16 by driving the metal
halides out of the ends of the light source 16.
1309~2
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The inner envelope 46 of the light source 16 has a
length in the range of about 8mm to about 2Omm,
sidewalls with a thic~ness in the range of about O.4mm
to about 1.5mm, neck portion~ with a dlameter in the
range of about 2mm to about 6mm and a central portlon
having an outer diameter in the range of about 4mm to
about 12mm. The shroud member 48 has an overall lenqth
in the range of about 14mm to about 30mm, an outer
diameter in the range of about 8mm to about 2Omm and
outer walls 48A having a thickness in the range of
about .4mm to about 1.5mm. The outer walls 48A are
separated from the main sidewalls of the inner envelope
46 by a predetermined distance 48B which is within
the range of about lmm to about 5mm. ~he separation
between the inner envelope 46 and the outer walls 48A
provide a chamber 48C between the inner envelope and
the shroud member having a volumetric case capacity in
the range of about lOmm3 to about lOOmm3. The
chamber 48C is preferably evacuated and preferably
contains a hydrogen and water getter 48D that is
dispersed about the inner surface of the outer walls
48A and which is preferably comprised of chips of
zirconium.
The light source 16 may have other embodiments such
as shown in Figs. 4 and 5 that use the same reference
number for similar elements with similar dimensions and
which are shown and described with regard to Fig. 3.
Fig. 4 illustrates a light source 16 in which an inner
envelope 46 formed of a quartz material is merged to a
shroud 48 formed of a type #180 glass material and in
which the inner leads 38 and 40 are sealed at opposite
neck portions of the glass shroud 48. Fig. S
illustrates a single-ended light source 16 in which the
electrodes 30 and 32 are disposed and exit from the
same end of the light source 16.
The light source 16 contains a fill consisting of
i30~4~2
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mercury and a metal halide. The light source may also
contain a xenon gas at a pressure at room temperature
in the range of about 2 atmospheres to about 15
atmospheres. The mercury contained in the metal halide
lamp is in an amount in the range of about 2mg to about
lOmg. The amount of mercury is chosen so that with a
bulb of a certain size and a distance between the
electrodes of a certain amount the voltage drop across
the lamp is a convenient value and such that the
ConvectiQn currents within the lamp that produce bowing
of the arc do not produce excessive bo~ing. The
operating pressure of the-light source 16 is in the
range of about 2 atmospheres to about 65 atmospheres.
The metal halide is a mixture of an amount in the range
of about 2mg to about 50 mg. The mixture is comprised
of halides selected from the group given in Table 1.
TABLE_1
Sodium Iodine
Scandium Iodine
Thallium Iodine
Indium Iodine
Tin Iodine
Dysprosium Iodine
Holmium Iodine
Thulium Ioàine
Thorium Iodine
Cadmium Iodine
Cesium Iodine
The metal halide light source 16 of the present
invention does not suffer the disadvantages of previous
metal halide lamps discussed in the "Background"
section. More particularly, the light source l~ has
means so as to (1) reduce the detrimental catephoresis
130~2
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effects suffered by the low frequency A.C. operation or
D.C~ operation of such a lamp; ~2) reduce the sodium
ion migration losses of the metal halide lamp; (3)
reduce the sodium losses caused by the photoelectrons
emission of metal structural members of the related
lamp; (4) reduce the hydrogen-oxygen detrimental
effects typically associated w~th a metal halide lamp;
(5) simplify the mounting structure for the metal
halide lamp: and (6) provide for containment of the
particles created by the remote possibility of the
rupturing of the metal halide lamp 16 operated at a
relatively high pressure. In addition, the metal
halide lamp because of its relatively small dimensions
is particularly suited for reducing the overall
dimensions of the related automotive headlamps finding
application in aerodynamically styled automobiles.
Typically when small, wattage metal halide lamps
not having the benefit of the present invention are
operated from a relatively low frequency of an
alternating current (A.C.) source such as 60 Hz or from
a D.C. power source, the metal halide ions are
influenced by the electric field created by these
excitation and have enough time, for example, during
each 60 Hz cycle to move a significant distance away
from the electrodes of the lamp. The effect called
catephoresis on these types of operation of the metal
halide lamp is to gradually sweep the halides into the
end regions of the lamp whereby these halides do not
make a substantial contribution to the amount of halide
occurring between the electrodes and therefore do not
contribute to the illumination desired for these low
wattaqe metal halide lamps. One of the contributing
factors of such detrimental operation is that the
convection effects on the outside of the metal halide
lamp cool the lower region of the metal halide lamp
which assists in condensing and drawing the metal
1309452
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halide ions away ~rom their desired location between
the electrodes.
The present invention surrounds the inner envelope
with a vacuum shroud so that the temperature of the
inner envelope i8 higher and more uni~orm by
eliminating both gas conduction and convection losses.
The structure of the light source 16 of the present
invention being formed of the inner envelope and shroud
member, each having the dimensions previously given
along with the separation between electrodes, are
selected to provide sufficient heat in the area of tha
inner envelope related to the separated electrodes that
thermally causes a diffusion to drive or move the metal
halide ions out of the end regions of the inner
envelope at a rate sufficient to cancel effects of
catephoresis.
The features of the present invention which reduce
the detrimental catephoresis, conduction and convection
effects are particularly advantageous in allowing the
metal halide lamp to be oriented, in a horizontal or
vertical arrangement relative to the base of the lamp
in which it is housed, so that the overall lamp may be
universally positioned to meet the various lighting
fixture needs in which the lamp may find application.
The present invention also provides a solution for
reducing the sodium ion migration problems typically
experienced for metal halide lamps. As previously
discussed, most metal halide lamps, including the
present light source 16, include sodium iodide as a
part of the fill and the sodium ions of such an
ingredient migrate from the lamp by electrolysis
through the fused silica during operation of such
lamp. As the sodium ions are lost and free iodine is
left behind in the arc tube, the desired illumination
of the metal halide lamps deteriorates through the loss
of sodium radiation, and in turn, t~e operating voltage
`` ~30~4~2
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of the metal halide lamp rises due to the free iodine,
ultimately to a point of possible lamp failure.
The shroud member 48 of the light source 16, having
the dimensions previously given, is of a suf~cient
importance in that the shroud member runs cool,
relative to the inner envelope and thereby reduces the
electrical conductivity of the shroud member by a
sufficient amount, so that the sodium ions which
diffuse through the inner envelope and settle on the
inside wall of the shroud are not electrically
neutralized, but rather produce a strong electric field
which stops or opposes the motion of subsequent
migrating sodium ions and thereby reduces and even
avoids any further related sodium loss.
lS The light source 16 also reduces the sodium ion migration that may typically be caused by metallic
members emitting photoelectrons when subjected to
incident radiation emitted from the light source as
discussed in the "Background" section. For example,
some of the photoelectrons emitted from metallic
members typically drift to the light source charging up
the surface of the light source to a negative
electrical potential which accelerates the electrolysis
of the sodium ions from the fused silica. The present
invention provides the shroud function without the need
of any metallic members positioni~ the shroud around
the inner envelope. The shroud 4~ merged and sealed
~`^ directly to the inner envelope thereby eliminating any
metal that would otherwise produce photoelectrons that
would disadvantageously contribute to the loss of
sodium ions. The shroud also prevents any
photoelectrons liberated from metal parts anywhere
inside the outer jacket from reaching the inner quartz
bulb.
The light source 16 of the present invention has
its hydrogen and water getter 48DI preferably
1309~2
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comprised of chips of zirconium metal, confined w~thin
the shroud so as to reduce the detrimental effects of
hydrogen and water which may diffuse out of the
discharge lamp. These metal chips located in the
chamber 48~ are electrically floating, that is the
chips do not have an establi6hed electrical potential,
and therefore do not contribute to the problem of
photoelectrons causing the migration of sodium ions.
A further advantage of the light source 16 is
related to the containment provided by the vacuum
shroud 48 bei~ng integrated with the inner envelope 46.
The shroud ~ being placed about the inner envelope,
c~
that is normally operated at a relatively high
pressure, retards or contains any possible
fragmentation caused by the unlikely rupturing of the
inner envelope. This containment helps in assisting
the capturing of these fragments so as to prevent these
fragments from fracturing the outer wall of an outer
envelope that may be used to house the metal halide
lamp of the present invention. This contribution is
provided by having the space between the inner envelope
and shroud evacuated so that it cancels some of the
pressure from the inner envelope and tend to slow down
any quartz or glass fragments that may be released from
the unlikely rupture of the inner envelope.
A further feature of the present invention is that
the shroud being formed with inner envelope simplifies
the mounting of such a shroud within the confines of a
lamp which houses the present invention.
It should now be appreciated that the present
invention provides for a metal halide lamp having means
to (1) reduce the detrimental catephoresis effects of
operating such a lamp from a low frequency (A.C.)
alternating current eource or D.C. sourcel (2) reduce
the typically experienced sodium migration problem from
the inner envelope and prevents photoelectrons creating
~3094~2
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sodium ions lo~ses, (3) provide for a containment
function of a highly pressurized inner envelope, and
t4) ~implify the mounting of a shroud for a highly
pressurized inner envelope.
The light source 16 of the present invention has
further advantages featured over prior art metal halide
lamps. One of these features is that the ahroud 48
disturbs or spreads the heat generated within the inner
envelope over a larger volume relative to the heat
distribution confined to the inner envelope itself.
This heat spreading is particularly advantageous to the
plastic or sealing arrangement typically encountered
within an automotive headlamp.
A further advantages is that the shroud 48 may be
formed with a mixture containing titanium oxide which
absorbs a substantial portion of the ultraviolet
electromagnetic radiation generated by the discharge
within the inner envelope 46 and thereby preventing
such ultraviolet radiation from reaching and degrading
the components comprising the automotive headlamp that
are susceptible to such radiation.
The light source 16 is also advantageous to the
placement of various coatings for different
application. The surfaces of the shroud 48 are at a
low temperature relative to the inner envelope 16 and
more readily accommodates infrared reflective films and
color films compared to the surfaces of the inner
envelope 16 or other prior art metal halide lamps. The
infrared films reflect the infrared radiation back
toward the inner envelope and raises its temperature
and thereby increasing its efficacy. The color film
may be of a yellow type to provide corresponding yellow
light advantageous for various lighting applications
such as automotive lighting used in foreign countries
such as France.
$he low temperature of the shroud relative to the
094~2
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inner envelope is also beneficial in masking or
controlling the light distribution for certain
application such as automotive technology. For
example, a black coating may be placed on one end of
shroud to prevent light from being emitted ~rom this
end so as prevent this light from encountering and
being reflected by a related portion of the reflector
12 that may produce unwanted or stray light for
automotive applications. The lower temperature of the
shroud 48 eases the problems of such placement of a
black coating relative to being placed onto the inner
envelope 46 or any known prior art metal halide light
source.
The metal halide light source 16 may be
advantageously operated by current interruption
operating circuit disclosed in U.S. Patent No.
4,857,810 of K.A. Roll et al., issued August 15, 1989,
assigned to the same assignee as the present invention,
to which reference may be made for further details of
its operation. The current interrupt operating circuit
controls the duty cycle of its described current
interrupt switch so as to maintain a predetermined
power level in the metal halide light source 16 of the
present invention. As discussed in the
above-referenced U.S. Patent 4,857,810, the system
efficiency of operating a discharge lamp, such as the
metal halide lamp 16, by means of current interruption
is contemplated to be an improvement in excess of 50%
relative to prior art methods of operating gas
discharge devices.
The metal halide lamp having relatively small
dimensions, previously given, provides for a light
source that is particularly suited for aerodynamically
styled automobiles and may be described with reference
to Figs. 6(A) and 6(B). Figs. 6(A) and 6(B) are
:`
~,
` ~3094~2
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interrelated and show a comparison of the divergence of
the beam produced by a headlamp using a tungsten
filament 116 compared to that produced by a headlamp
having the smaller metal halide light source 16 of the
present invention. Fig~ 6~A) shows the light source
116 indicated in the form of an arFow having its
mid-portion located the focal ~ 26 along the axis
28 of the reflector 12, whereas, Fig. 6(B) shows the
light source 16 in the form of anla~r~ having its
mid-portion located at the focal poi~t 26 along the
axis 28 of reflector 12 having the same dimensions as
of Fig. 6(A). The incandescent light source 116 may
have a length such as 5mm as discussed with regard to
Fig. 2, whereas, the light source 16 has a length of
approximately 3mm discussed with regard to Figs. 3, 4,
and 5.
The incandescent filament 116 when activated
provides for a plurality of reflected light rays that
diverge at a rate which is proportional to the size of
the light source 116 and is represented by the angle
eA. Similarly, the xenon light source 16 provides
for a plurality of light rays that diverge from each
other by an angle ~B.
With reference to Fig. 6(A), the angle of
divergence of the filament 116 is illustrated by a
light ray 116A emitted from the upper most portion of
filament 116 which is intercepted and reflected by
reflector 12 as light ray 116B. The angle between
the light ray 116B which passes through the focal
point 26 and the axis 28 is the divergence angle ~A
of filament 116. For the values previously given to
the filament 116 (5mm) and the reflector 12 (focal
length 25mm), this angle 6A is 11.3.
Fig. 6(B) shows light rays 16A and 16B which
are similar to light rays 116A and 116B and
dessribe with regard to Fig. 6~A). The angle of the
13091~2
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divergence ~B produced by the llght rays emitted by
the light source 16, for the previously given values of
the light source 16 (3mm) and the reflector 12 ~focal
length 25mm), is 6.80. The angle o~ divergence ~B
is approximately three-fifths smaller than the angle of
the divergence ~A. The overall effect of such light
produced by the light source 16 is that a desired beam
pattern, developed by the automotive headlamp 10 of the
present invention and directed to a roadway has less
spread and may therefore be directed where it is needed
to illuminate the road with less light where it is not
wanted. The reduction of this spread or unwanted light
by the metal halide light source 16, relative to an
incandescent light source 116, reduces the veiling or
concealing effect of fog, rain and snow and thereby
provides more useful direct light for automotive
applications.
A further advantage provided by the relatively
small size of the metal halide light source 16 is to
reduce the necessary size of the reflector of the
automotive headlamp and may be described with reference
to Figs. 7(A) and 7(B). Figs. 7(A) and 7(B) are
respectively similar to Figs. 6(A) and 6(B) and use
similar reference numbers where applicable. Figs. 7(A)
and 7(B) are different in that the focal length 26 has
been reduced by a factor of two (2) relative to the
focal length 26 respectively shown in Figs. 6(A3 and
6(B). Further the reflector 12 of Figs. 7(A) and 7~B)
has been reduced in height by a factor of about 2/3
relative to that of Figs. 6(A) and 6(B).
Fig. 7(A) shows that the tungsten incandescent
filament 116 produces light rays 116A and 116B in
which ray 116B forms an angle of divergence ~C
having a value of about 21.8 for the reflector of
Figs. 7(A) and 7(B) and previously given values of
filament 116 (Smm length) which would produce stray
~309A~
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light in a beam pattern of a sufficient amount that
would not meet the needs of the automotive technology.
Conversely, Fig. 7(B) shows the light source 16 of
about 3mm producing liqht rays 16A and 16~ in which
ray 16B forms an angle of divergence ~D having a
value of about 13.5 which produces a beam pattern
having a limited amount of stray light so as to more
than meet the needs of the automotive technology. The
effect of the smaller size light source 16 allows for
an increase in the collection efficiency of the
reflector 12 through a reduction in its focal length
and a slightly smaller reduction in its overall
dimensions. The overall effect is that the light
source 16 allows for both decreasing the size of the
reflector and improving the collection efficiency of
the reflector by sufficient amounts so as to allow the
automotive designer to decrease the hood lines of the
automobile as discussed in the "~ackground" section.
It is contemplated that the practice of the present
invention allows for a reduction of the reflector for
an automotive headlamp ~y a factor of 2/3 relative to
prior automotive headlamp utilizing a typical
incandescent filament so that the hood lines of the
automobile may be correspondingly reduced.
The overall reduction of the dimensions of the
reflector and thereby the corresponding dimensions of
the automotive headlamp may be illustrated with
reference to Figs. 8(A) and 8(B~. Fig. 8(A) is a
perspective view illustrative of a prior art
rectangular automotive headlamp employing an
incandescent filament and having similar elements of
the automotive headlamp 10 of Figs. 1 and 2 with
corresponding reference numbers that have been
increased by fac~or of 100. Fig. 8(B) is a
3~ perspective view illustrative of one embodiment of the
present invention ~eing a rectangular automotive
1309~5~
- 20 - LD 9804
headlamp 10 shown in Figs. 1 and 2 and having dimensions
that have been reduced relative to the prior art lamp 110
by a factor of about 40% in accordance with the
description of the lamp 10 given hereinbefore. From a
comparison between Fig. 8(A) of the prior art lamp 110
and Fig. 8(~) it may be easily seen that the practice of
the present invention provides the automotive designers
with the means in the form of the light source 16 to
substantially reduce the hood lines of the automobile.
It should now be appreciated that the present
invention provides for a metal halide light source for an
automotive headlamp that allows for substantial
reductions in the hood line of the automobile. It should
also be appreciated that the light source 16 of the
present invention may contain a fill of xenon in the
amount previously specified and obtain the benefits
previously described herein in addition the benefits
described in the cross-referenced Canadian Patent
Application Serial No. 589,943.
Although the previously given description of the
metal halide lamp along with metal halide lamp having a
fill of xenon was related to automotive application, it
is contemplated that the practice of this invention is
equally applicable to other various lighting
applications. A significant feature of the present
invention is that light is generated by metal halide lamp
16 having small dimensions relative to prior art metal
halide lamps. The feature of providing discharge type
lighting from the relatively small light source of the
present light source allows it to be advantageously
utilized in various lighting applications, homes, office
and other various commercial and industrial environments
and correspondingly reduce the related mounting and
focussing arrangements.
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