[0001] This invention is related to U.S. Patent Application Serial No. having attorney Docket
No. LD 9150, entitled "Improved Metal Halide Lamp and Lighting Systems Particularly
Suitable for Architectural Lighting," filed concurrently herewith and assigned to
the same assignee as the present invention.
BACKGROUND OF THE INVENTION
[0002] This invention relates to metal halide lamps, and more particularly, to metal halide
lamps and lighting systems suitable for architectural lighting.
[0003] Metal halide lamps currently available can be broadly divided into two classes. One
class of lamps has a quartz envelope housing a very compact electrode- stabilized
arc used as its light source. The quartz envelope is generally spheroidal with a wall
loading characteristic in the range of 50 to 100 watts/sq. cm of arc tube surface
which typically yields a useful life of a few hundred hours. The other class of lamps
is referred to as general purpose metal halide lamps having a cylindrical quartz envelope
housing a wall stabilized arc. A typical wall loading characteristic for these lamps
is in the range 5 to 15 watts/sq. cm of arc tube surface which yields a very long
useful life typically 15,000 hours.
[0004] The lamps having a compact light source are used frequently in stage and studio applications.
The compact light sources are desirable when used in cooperation with reflectors because
the compact light sources afford a great deal of freedom to lighting designers in
the selection of desired beam patterns. That is, a lamp may be provided having a beam
pattern which is very narrow, such as preferably used in a spot light, or if desired,
a lamp can be provided having a diffused beam pattern which is accomplished by locating
the compact light source off-center from the focal point of the reflector of the lamp
or by using appropriate diffusing lenses.
[0005] The compact light source when used with a spherical or parabolic reflector usually
provides a symmetrical beam pattern which can have certain limitations. For architectural
lighting it is considered important that asymmetrical beam patterns be provided which
permit overlapping of the beam illuminating patterns so that, for example, particular
features of a building may be highlighted. The overlapping is further advantageous
in that a failure of one of the plurality of illuminating lamps does not cause a complete
loss of the illumination of the building related to the failed lamp.
[0006] Metal halide lamps while having desired illuminating characteristics also have certain
disadvantages which have heretofore hindered their usage for architectural lighting.
The metal halide technology used in the development of compact light sources necessitates
that the chemistry of the lamp be such that the compact light source, as previously
mentioned, has relatively high wall loading characteristics, which ordinarily result
in short life, typically 50 hrs. to 500 hrs.
[0007] The relatively short life of these compact light sources is not disadvantageous for
stage and studio applications. However, the typical 50 to 500 hours life is disadvantageous
for architectural lighting where it is desired that metal halide lamps be provided
having a life expectancy of at least approximately 2000 hours and somewhat greater
than approximately 4000 hours.
[0008] In other applications such as for general lighting, metal halide lamps are relatively
larger in size; this provides a more diffused pattern when used in cooperation with
a selected reflector. Ordinarily when a high intensity discharge lamp, such as a metal
halide lamp, is employed in general lighting applications, the arc tube serving as
the light source is placed within an outer envelope in order that it can be surrounded
by an inert gas atmosphere to control the temperature and to remove oxygen from the
environment. Further, ordinarily in general lighting, lamps utilizing a relatively
large envelope provide their desired function, but the large outer envelope presents
several disadvantages. For example, the large outer envelope may distort the beam
pattern and can, on many occasions, prevent the light source from being advantageously
placed relatively close to the reflector surface and thereby hinder the attainment
of a desired beam pattern. The lack of beam control normally encountered with general
lighting devices having large outer envelopes and providing diffused light patterns
hinder their usage in architectural lighting.
[0009] In addition to the above-described drawbacks of general purpose metal halide lamps,
when lamps with a relatively large light center length are used for architectural
lighting, any small misalignment in the base of the lamp produces a relatively large
displacement of the light source relative to the focal point of the reflector which
commonly causes the desired beam pattern to be unfavorably altered. This unwanted
displacement typically necessitates realignment of the light source in the fixture
and can in some cases necessitate realignment of the fixture itself. It is therefore
considered important to provide lamps which have accurate mounting and which lamps
can be easily mounted in such a way that deviations from a desired position of the
light source within the reflector do not occur even during lamp replacement procedures.
Additionally, since the light fixtures and sources are initially carefully aligned,
it is desirable that readjustment and realignment be unnecessary each time light sources
are replaced.
[0010] A further factor which should be considered with regard to architectural lighting
is the overall size of the light source and the overall size of the outer envelope.
Attempts to reduce the overall size of the outer envelope encounter a problem related
to an increase in the electromagnetic field to which the arc discharge is subjected
from the current return lead located in proximity to the arc tube. The increased electromagnetic
field creates a condition in which the arc is forced close to the walls of the arc
tube leading to excessive temperatures. The walls of subjected arc tube begin to bulge
outward and thus shorten the life of the arc tube. It is desired that means be provided
which allow compacting the size of the outer envelope without encountering the typically
expected shortening of the life of the arc tube.
[0011] With regard to the size of the light sources, if the light sources are relatively
large necessitating a relatively large fixture, the light sources along with the fixtures
need to be placed a relatively long distance away from the building exterior desired
to be illuminated in order not to interfere with the aesthetics of the architecture.
The remote location may cause the illuminated features of the building often to appear
as washed out due to inadequate illumination, and further, much of the illuminating
light spills out of desired beam patterns so as to be wasted light which does not
illuminate the exterior of the building.
[0012] Accordingly, objects of the present invention are to provide a metal halide lamp
not having the previous mentioned limitations but which are particularly suited for
architectural lighting having, (1) particular applicability to building exteriors,
(2) an asymmetrical beam pattern so as to provide overlapping and highlighting of
the features of the building being illuminated, (3) accurate mounting of the metal
halide lamps in their related fixtures so as to provide a desired uniformity of beam
patterns and also to provide for reproducibility of the beam patterns upon subsequent
replacement of the metal halide lamps, (4) a relatively compact outer envelope having
means to substantially reduce the typically expected shortening of the life of the
arc tube housed in such an envelope, and (5) a relatively high anticipated life of
approximately 2000 to approximately 4000 hours and even greater.
[0013] These and other objects of the present invention become more apparent upon consideration
of the following description of the invention.
SUMMARY OF THE INVENTION
[0014] In accordance with the present invention a metal halide lamp particularly suitable
for architectural lighting is provided. The metal halide lamp comprises an arc tube
rigidly supported in an outer envelope having at least a pair of electrically conductive
leads located on opposite sides of the arc tube and connected to a primary electrode
of the arc tube. The arc tube comprises an inert gas, and a mercury vapor in the range
of about 170 mg to about 180 mg effective to establish an A.C. operating voltage for
the arc tube in the range from about 250 volts to about 300 volts. The arc tube further
comprises a halide which develops a vapor during operation. The halide is selected
from the group consisting of (1) sodium iodide, scandium iodide, thorium iodide, cadmium
iodide, and mixtures thereof, (2) sodium iodide, scandium iodide, thorium iodide,
cadmium iodide, mixtures of the selected halide iodide, and the metal cadmium additive
to the selected halide iodide and to the mixture of the selected halide iodides, and
(3) the metal cadmium.
[0015] The present invention may best be understood by reference to the drawing and the
detailed description of the preferred embodiments shown therein.
BRIEF DESCRIPTION OF THE DRAWING
[0016]
FIG. 1 shows a metal halide lamp in accordance with one embodiment of the present
invention.
FIG. 2 shows the arc tube of the present invention.
FIG. 3 illustrates the functional arrangement of the metal halide lamp of FIG. 1 relative
to a reflector so as to provide a desired oblong beam pattern related to the present
invention.
FIG. 4 illustrates the oblong beam pattern projected on a typical building.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] FIG. 1 illustrates one embodiment of the present invention of a metal halide lamp
10 particularly suitable for architectural lighting. The lamp 10 comprises a glass
outer envelope or jacket 12 of an ellipsoidal shape with a relatively narrow diameter
typically of 12 cm and having a neck 14 to the end of which is attached a screw base
16. The neck 14 is closed by a reentrant stem 22 having a press portion through which
extends relatively stiff inleads 24 and 26. The inleads 24 and 26 are connected externally
to the contact surface of the base, namely the insulated center contact or eyelet
18 and the base shell 20.
[0018] The lamp 10 further comprises an inner arc tube 42 which is provided at opposite
ends with a pair of main discharge supporting electrodes 50 and 58. The main electrode
50 is connected to one inlead by means of an inlead 48, a foil portion 46, an external
lead 44, and a pair of fly-leads 40A and 40
B. These fly-leads 40A and 40
B are of primary importance to the present invention as to be described.
[0019] The main discharge electrode 58 is connected to the other inlead 26 by means of an
inlead 56, a foiled portion 54, an external lead 52, an electrically conductive member
60, and a side rod 28. The foiled portions 46 and 54 are comprised of molybdenum and
have a desired coefficient of expansion to provide respectively for proper sealing
of the opposite ends of arc tube 42.
[0020] The side rod 28 is welded to the inlead 26 and has a loop portion 28 which provides,
by means of support and strap member 30, support for one end of the arc tube 42. The
other end of arc tube 42 is supported within the outer envelope 12 by a cross member
32 which is attached at each end to a U-shaped support member 34 anchored to a dimple
38 at the dome of the envelope 12 by engagement of a loop clip 36.
[0021] The arc tube 42 further comprises an auxiliary electrode 62 which is connected to
the relatively thick inlead 24 by means of a foil member 64 similar to foil members
46 and 54 of arc tube 42, an inlead 66 of arc tube 42 and a series resistor 70. In
operation the auxiliary electrode 62 is connected to a main electrode 58 by means
of a thermal switch 78 which is connected to a conductor member 60, which, in turn,
is connected to the previously described side rod 28 having a connection to the relatively
thick inlead 26. The thermal switch 78 short-circuits the starting electrode 62 to
the main electrode 58 after the arc tube 42 has warmed up and achieved its starting.
Such a thermal switch is described in U.S. patent 3,965,387 which is assigned to the
same assignee as the present invention and is herein incorporated by a reference.
[0022] The arc tube 42 shown in detail in FIG. 2 is of the double-ended type and has typically
dimensions of a length of 120 mm, a width of 20 mm, and a thickness of 2 mm and is
designed to operate at 1500 watts. The arc tube 42 is comprised of a material selected
from the group consisting of fused silica, mullite and alumina.
[0023] The arc tube 42 contains a filling comprising metals and halide along with a mercury
vapor. The halide and the mercury vapor droplet have respective weight ratios of about
1:7 to about 1:3. The halide develops a vapor during the operation of the arc tube.
The halide is selected from the group consisting of sodium iodide, scandium iodide,
thorium iodide, cadmium iodide and halide mixtures of the selected halide iodide.
Still further, for one embodiment to be described, the halide is preferably selected
as a compound sodium iodide including cadmium.
[0024] As discussed in the "Background" section above, attempts to reduce the overall size
of the outer envelope housing an arc tube such as arc tube 42 have encountered an
increase in the electromagnetic field to which the arc tube is subjected causing a
decrease in the life of the arc tube itself. It is of primary importance that the
present invention provides means to substantially reduce the unwanted effects of the
increased electromagnetic field while still housing the arc tube 42 in a relatively
compact outer envelope 12.
[0025] Initially in our housing of the arc tube 42 into the relatively compact envelope
20 it was discovered that the walls of the operating arc tube 42 developed an outward
bulge detrimental to the life of the arc tube 42. The initial housing for the arc
tube 42 had a single fly-lead such as 40A shown in FIG. 1. It was discovered that
the increased electromagnetic field from the current in the single fly-lead were causing
the arc within the arc tube to undesirably be dislocated from the axial central region
of the arc tube toward the walls of the arc tube. This dislocation was causing the
detrimental bulging of the arc tube 42. In order to substantially prevent this dislocation
it was determined that effects of the increased electromagnetic fields needed to be
reduced. Such a reduction is accomplished by the practice of the present invention.
[0026] The lamp 10 of FIG. 1 by means of at least a pair of fly-leads 40A and 40
B, positioned on opposite sides of the arc tube 42, provide a pair of current return
leads for one of the primary electrodes effective to reduce the electromagnetic field
to which the arc tube 42 is subjected. The effect of a pair of looped wires 40A and
40
B is to cause the arc of the arc tube 42 to be substantially maintained in its desired
axial central region of the arc tube effective to substantially inhibit any reduction
in the life of the arc tube with regard to the increased electromagnetic field.
[0027] As further discussed in the "Background" section above, it is desired to have a compact
light source, such as arc tube 42, for architectural lighting that provides a warm
incandescent light color temperature. As further discussed, the obtainment of an incandescent-like
color for arc tube containing a metal halide, such as arc tube 42 usually creates
undesired high wall temperatures of the arc tube, which, in turn, decreases the operating
life of the arc tube and the metal halide lamp itself.
[0028] In the practice of the present invention the arc tube 20 provides an incandescent-like
color achievable without elevating the wall temperatures of the arc tube that would
result in the usually expected decreased life of the arc tube 42. This is primarily
achieved by the particularly advantageous group of metal halides given above, including
the compound sodium iodide, in combination with the use of cadmium which additionally
lowers the color temperature nearer to incandescent. It is preferred that the metal
halide and cadmium have respective percentage weight ratios of about 40 and about
1. The combination of these features not only achieves the desired color, but also
increases the efficacy of the light source with only a relatively small reduction
in the useful life.
[0029] Another factor of the present invention related to useful life of the metal halide
lamp 10 is the A.C. operating voltage of the arc tube 42. This operating voltage is
primarily determined by the amount of mercury contained in the arc tube 42. The amount
of mercury vapor contained in the arc tube 42 is selected to effectively establish
an A.C. operating voltage for the arc tube 42 in the range of about 250 volts to about
300 volts. For the dimensions previously given for arc tube 42 and for this range
of about 250 volts to about 300 volts, the selected amount of the mercury vapor is
in the range of about 170 mg to about 180 mg.
[0030] The arc tube 42 having the A.C. operating voltage range, the mercury vapor, the halide
gas and the dimensions all noted above, although having a relatively high wall loading
characteristic such as 20 watts per cm
2, yields an anticipated life of approximately at least 2000 hours and somewhat greater
than approximately 4000 hours which is particularly advantageous for architectural
lighting related to the present invention. This 2000 to 4000 hour anticipated life
is intermediate between stage and studio lamps, having an anticipated life of about
50 to 500 hours, and the general purpose metal halide lamps having an anticipated
life in the order of 15,000 hours.
[0031] The metal halide lamp 10 of FIG. 1 is of a relatively high wattage in the order of
1500 watts which is particularly advantageous for architectural lighting desiring
an intense illuminating light source so that the exterior features of the building
may be highlighted. The high wattage lamps allow for a lower number of fixtures to
illuminate the building.
[0032] The operating arc tube 42 yields a warm incandescent-like color which is particularly
suitable for illumination of the outside of buildings and various architectural construction.
For example, the metal halide lamp 10 of FIG. 1 having the arc tube 42 is particularly
suitable for certain types of limestone exteriors found on buildings. The operating
halide lamp 10 has a correlated color temperature of about 3400°K to about 3900°K
which substantially approaches that of an incandescent lamp.
[0033] A further feature of the present invention is the accurate and fixed positioning
of the light source 42 in the metal halide lamp 10 so as to obtain uniformity in the
beam pattern transmitted by one or more lamps 10. The present invention accomplishes
uniformity by, (1) a double-ended light source 42 so that each of its ends is correctly
positioned and aligned relative to a reflector cooperating with lamp 10 to achieve
desired illumination, and (2) a light source 42 having a relatively small light center
length.
[0034] The double-ended light source 42 is shown in FIGS. 1 as rigidly clamped and is positioned
relative to the focal point of lamp 10 by an accuracy in the range of about 3 mm.
This accurate positioning of light source 42 in turn provides an accurate and predetermined
placement of the metal halide lamp 10 relative to the desired location of a reflector
for which the metal halide lamp 10 is advantageously employed.
[0035] The lamp 10 has a light center length which is meant to represent the distance between
the center of the arc and the bottom base contact of the lamp 10 which is about 160
mm. This relatively small light center lig]`t provides a compact light source 42 that
may be accurately positioned within the lamp 10. The midsection of the arc tube 42
may be predeterminedly located within a range of about 1 to about 20 mm, relative
to the focal point of the reflector for which it is utilized so as to develop an asymmetrical
beam pattern particularly suitable for architectural lighting. This arrangement develops
an oblong light source which results in an asymmetrial beam pattern. The asymmetrical
beam pattern allows for overlapping of the light transmitted by a plurality of metal
halide lamps 10 so that desired features of the exterior of the building being illuminated
may be highlighted and also preventing a complete loss of a portion of the building
being illuminated from occurring upon a failure of any one particular metal halide
lamp 10.
[0036] The metal halide lamp 10 substantially reduces the misalignment problems of the light
source location relative to the focal point of the reflector which would otherwise
cause the desired beam pattern emitted by the cooperation between the lamp and reflector
to be undesirably altered. Further, the metal halide lamp 10 by its accurate and rigidly
fixed light source 42 provides for repeatable and accurate mounting from fixture to
fixture thus eliminating any misalignment problems between the metal halide lamp 10
and its cooperating reflector that may otherwise occur during lamp replacement procedures.
[0037] It should now be readily understood that the present invention provides architectural
lighting designers with a metal halide lamp 10 used with a reflector unit which can
be accurately positioned at the time of the original installation. Further, if a metal
halide lamp burns out and maintenance is necessary, the replacement light source used
with the reflector is accurately positioned relative to the reflector unit.
[0038] Another important feature of the present invention is the outer envelope 12 of the
halide lamp 10 which reduces interference with the beam pattern. This is accomplished
by an outer envelope 12 having a relatively narrow diameter such as an E37 hard glass
bulb.
[0039] The metal halide lamp 10 is functionally illustrated in FIG. 3 for an illuminating
lighting fixture 84 having a reflector device 74. The reflector may have an aperture
of 60 cm and a radius of curvature of 20 mm. The metal halide lamp 10 is preferably
positioned so that the midsection of the arc tube 42 is located at the focal point
76 of reflector 74. The ballast circuitry for operating the metal halide lamp 10 is
lodged in a housing 80 and the necessary power and control functions related to the
ballast circuit are routed to the metal halide lamp by cabling 78.
[0040] The metal halide lamp 10 in cooperation with reflector 74 transmits a plurality of
rays 86A, 86
8, 86
c and 86
N that combine into an oblong beam pattern 86 shown in FIG. 3 which is particularly
suited for architectural lighting. More specifically, the oblong beam pattern 86 does
not have the limitation of a narrow beam pattern or a diffused beam pattern both as
discussed in the "Background" section. More particularly, the oblong beam pattern
86 is particularly suited for illuminating the exterior of a limestone building as
illustrated in FIG. 4.
[0041] FIG. 4 illustrates a portion 88 of an exterior of a building having limestone bricks
90. The beam pattern 86 developed by the 1500 watt metal halide lamp 10 provides for
up to 60 footcandles depending on the number of fixtures and distance of the fixtures
away from the building being illuminated. The high wattage of lamp 10 allows for locating
the lamp 10 and their related fixtures away from the illuminated building which, in
turn, allows the metal halide lamps 10 to be hidden in structures away from the building
themselves and at places where the maintenance of metal halide lamps 10-along with
the reflectors 74 may be easily achieved. Further, a plurality of metal halide lamps
10, each having a respective reflector 74, can be arranged to form a lighting system
so as to produce overlapping beam patterns shown in FIG. 4 as phantom lines 92 and
94. The overlapping is accomplished by suitable alignment of the various fixtures
84. The overlapping of the beam patterns provides for desired illumination of the
building even in the event of a lamp 10 failure.
[0042] In accordance with the present invention the metal halide lamps 10 were tested in
experimental fixtures and provided desired beam control with a Correlated Color Temperature
of 3600°K.
[0043] It should now be appreciated that the practice of the present invention provides
a metal halide lamp 10 particularly suitable for architectural lighting and having:
(1) particular applicability to the exteriors of buildings; (2) when used in cooperation
with a reflector unit, in accordance with the hereinbefore given description, provides
an asymmetrical beam pattern so that overlapping and highlighting of the building
being illuminated are achieved; (3) accurate mounting for related reflector units
so as to provide a desired beam pattern and also provide for reproducibility of the
beam pattern upon subsequent replacement of the metal halide lamp 10; (4) a relatively
compact outer envelope having means to reduce the effects of the electromagnetic field
to which the arc tube is subjected so as to substantially inhibit the typically encountered
shortening of the life of the arc tube itself for such an envelope; and (5) a relatively
high anticipated life of at least approximately 2000 hours and slightly greater than
4000 hours.
1. A metal halide lamp particularly suitable for architectural lighting comprising
a light-transmissive outer envelope, an arc tube rigidly supported within the outer
envelope and having primary thermionic electrodes sealed in the opposite ends thereof
and an auxiliary electrode located adjacent to one of said primary electrodes;
said rigidly supported arc tube having at least a pair of electrically conductive
leads located on opposite sides of said arc tube and connected to one of said primary
electrodes;
said arc tube further comprising;
an inert gas;
a mercury vapor in the range of about 170 mg to about 180 mg effective to establish
an A.C. operating voltage for said arc tube in the range from about 250 volts to about
300 volts; and,
a halide which develops a vapor during operation said halide being selectable from
the group consisting of (1) sodium iodide, scandium iodide, thorium iodide, cadmium
iodide and mixtures thereof, (2) sodium iodide, scandium iodide, thorium iodide, cadmium
iodide, mixtures of the selected halide iodide, and the metal cadmium additive to
the selected halide iodide and to the mixture . of the selected iodides, and (3) the
metal cadmium.
2. A metal halide lamp according to claim 1 wherein the metal halide is preferably
sodium iodide and cadmium having respective percentage weight ratios of about 40 and
about 1.
3. A metal halide lamp according to claim 1 wherein said arc tube is a double-ended
type and has a length of about 120 mm, a width of about 20 mm and a thickness of about
2 mm.
4. A metal halide lamp according to claim 1 wherein the metal halide and the mercury
vapor have a respective weight ratio of about 1:7 to about 1:3.
5. A metal halide lamp according to claim 1 having an anticipated life of at least
2000 hours and somewhat greater than 4000 hours.
6. An illuminating light fixture comprising a metal halide lamp according to claim
1 and a reflector; said metal halide lamp being located relative to said reflector
effective to position the midsection of said arc tube substantially at the focal point
of said reflector fixture.
7. An illuminating lighting system comprising a plurality of metal halide lamps according
to claim 1 and a reflector for each of said lamps;
each of said lamps being located relative to its respective reflector effective to
position the midsection of each arc tube substantially at the focal point of said
respective reflector.