Metal halide discharge lamp with a quartz discharge vessel and a

Details Metal halide discharge lamp with a quartz discharge vessel and a Metal halide discharge lamp with a quartz discharge vessel and a

1996-06-25

1998-12-29

Patidar, Jay M.

Electric lamp and discharge devices

With gas or vapor

Envelope composition

313112, 313 25, 313570, H01J 6130

Patent

active

058545352

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to methal halide discharge lamps with a sodium containing ionizable fill.


BACKGROUND

Metal halide lamps have long life and light of high quality and are therefore suitable for indoor illumination, for example, of entrance halls and salesrooms and for residential lighting. They have a warm white to neutral white color, that is, a color temperature of about 2500 to 5000 Kelvin which is obtained by a sodium additive in the ionizable fill. A technical problem observed with all sodium containing high-pressure discharge lamps is the occurrence of loss of sodium from the ionizable fill in the discharge vessel, caused by diffusion of the sodium ions through the wall of the discharge vessel. This problem is particularly acute with metal halide lamps of low power rating whose ionizable fill has a low sodium content, and with metal halide lamps operated at unsaturated sodium vapor pressure. The loss of sodium from the fill in the discharge vessel causes a change in the color temperature, increases the ignition voltage and, finally, leads to premature failure of the lamps.
The European Patent Application EP 0 464 083 discloses a lamp as described above. To avoid loss of sodium, the lamp also has an outer envelope of low thermal loading which consists of highly pure quartz glass of low electrical conductivity. A disadvantage of this solution is that a comparatively expensive raw material is required for the outer envelope in order to avoid loss of sodium. Also, the desired low thermal loading of the, outer envelope requires relatively large spacing of the outer envelope from the discharge vessel. This increases the outer dimensions of the lamp and may lead to problems when fitting the lamps into the fixtures intended therefor.
The U.S. Pat. No. 5,111,104 describes a metal halide lamp having a color temperature of about 3600 Kelvin and a luminous efficacy of about 90 lm/W. Its discharge vessel is surrounded by an evacuated outer envelope to avoid loss of sodium from the fill in the discharge vessel. The outer envelope, in turn, is surrounded by a gas-tightly closed second outer envelope filled with inert gas. The second outer envelope, however, increases the manufacture costs of the lamp.
The U.S. Pat. No. 5,196,759 discloses a lamp comprising a light source which emits UV and visible light radiation. The light source is surrounded by a UV-absorbing and visible light transmissive fused quartz envelope codoped with titanium dioxide and cerium oxide to absorb at least a portion of said UV radiation and wherein said envelope is at a temperature above 500.degree. C. during operation of the lamp. The dopants of the quartz envelope suppress the harmful portion of the UV-radiation generated by the light source.
The U.S. Pat. No. 3,662,203 describes a high pressure metal vapor discharge lamp with saturated vapor in operating condition of the lamp comprising a discharge vessel and a double ended cylindrical outer envelope both of thermally highly loadable material permitting an operating temperature exceeding 500.degree. C. The spacing between the inner diameter of the outer envelope and the outer diameter of the discharge vessel is defined by a ratio of from 3:1 to 1.05:1 to provide additional heating of the discharge vessel by heat which is generated by the discharge and partially reflected by the outer envelope.


THE INVENTION

It is the object of the invention to provide a metal halide lamp of the type described which has a longer life and sufficiently constant operating parameters and quality of light over the life of the lamp.
Briefly, the sodium loss from the ionizable fill in the discharge vessel is reduced, in accordance with the invention, by providing the metal halide lamps with an outer envelope of quartz glass comprising a UV doping material in the material of the outer envelope can be seen from the curves of FIGS. 3 and 4.
FIG. 3 shows the lamp operating voltage (in volts) plotted above the time of operation of the lamp (in hours). Curve 1 shows the characteristic o

REFERENCES:
patent: 3662203 (1972-05-01), Kuhl et al.
patent: 4717852 (1988-01-01), Dobrusskin et al.
patent: 4825127 (1989-04-01), Krasko et al.
patent: 5057743 (1991-10-01), Krasko et al.
patent: 5111104 (1992-05-01), Hunter
patent: 5196759 (1993-03-01), Parham et al.

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