EP0377899A2

EP0377899A2 - Lighting discharge lamp

Info

Publication number: EP0377899A2
Application number: EP89124095A
Authority: EP
Inventors: Mitsuo Narita
Original assignee: Ushio Denki KK
Current assignee: Ushio Denki KK
Priority date: 1989-01-12
Filing date: 1989-12-28
Publication date: 1990-07-18
Also published as: EP0377899A3; JPH02186552A

Abstract

A lighting discharge lamp includes a light-emitting tube in which a halogen and lutetium are sealed together with mercury and a rare gas. The sealed amount of lutetium falls in a range of from 2 x 10⁻⁷ mol/cc to 2 x 10⁻⁵ mol/cc. The premature clouding of the light-emitting tube can be avoided to enhance its luminous flux utilization and the variations of its color temperature depending on those of supply power for operation can be reduced to a small extent.

Description

BACKGROUND OF THE INVENTION

1) Field of the Invention:

This invention relates to a lighting discharge lamp.

2) Description of the Related Art:

It is necessary for lighting discharge lamps employed in studios by way of example to emit white light with high efficiency, have excellent color rendering properties and be almost of a point source. For this purpose, so-called short-arc metal halide lamps in which a halide of a rare earth element is sealed within a light-emitting tube and the ratio of an interval between both electrodes to the maximum inner diameter of the light-emitting tube is small are used advantageously.
Conventional short-arc metal halide lamps have however been accompanied by a problem that the materials of their light-emitting tubes react with rare earth element halides sealed therein during their operation, whereby the walls of their light-emitting tubes become cloudy in their premature stage to result in the reduction of their luminous flux utilization. Besides, there have been, in some cases, a problem that their color temperatures decrease gradually during the operation, whereby subtle variations in color temperature occur.
Owing to the development of electric power units, it has recently been possible to regulate the quantity of light by controlling supply power for operation. However, the conventional short-arc metal halide lamps have involved a problem that their color temperatures vary to a great extent depending on the variations of the supply power for operation, whereby the color tones of light change due to the regulation of the light quantity.
With the foregoing in view, the present inventor has carried out an extensive investigation. As a result, it has been found that when lutetium is sealed in a specific proportion within a light-emitting tube, high color rendering properties can be obtained while maintaining the emission of white light with high efficiency and the above problems can be solved, leading to completion of the present invention.

SUMMARY OF THE INVENTION

An object of this invention to provide a lighting discharge lamp, which is free from premature clouding of its light-emitting tube to enhance its luminous flux utilization and undergoes only a little variation in color temperature depending on those of supply power for operation.
In one aspect of this invention with a view toward attaining the above object of this invention, there is thus provided a lighting discharge lamp comprising a light-emitting tube in which a halogen and lutetium are sealed together with mercury and a rare gas. The sealed amount of lutetium falls in a range of from 2 x 10⁻⁷ mol/cc to 2 x 10⁻⁵ mol/cc.
Since a halogen and lutetium are sealed together with mercury and a rare gas within a light-emitting tube in the lighting discharge lamp according to this invention and the sealed amount of lutetium is controlled in a specific proportion, the premature clouding of the light-emitting tube is avoided, as will be understood from the description of the Experimental Examples which will be described subsequently, so that its luminous flux utilization is increased, and moreover the variations of its color temperature depending on those of supply power for operation are reduced to a small extend, thereby obtaining light of an excellent color tone. Although the reasons why such excellent effects are exhibited are not understood fully, one of these reasons is thought to attribute to the fact that lutetium halide is stable and its vapor pressure is low.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a lighting discharge lamp;
FIG. 2 diagrammatically illustrates the relation between the sealed amount of lutetium and luminous efficiency:
FIG. 3 diagrammatically illustrates the spectral distribution of a lighting discharge lamp in Experimental Example 2;
FIG. 4 diagrammatically illustrates the relation between the operation time and color temperature of a lighting discharge lamp; and
FIG. 5 diagrammatically illustrates the relation between supply power for operation and the color temperature of a lighting discharge lamp.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[Example]

The present invention will hereinafter be described specifically by the following Example.
In this Example, a lighting discharge lamp is fabricated by sealing a halogen and lutetium in a specific proportion together with mercury and a rare gas within a light-emitting tube 10 made of, for example, quartz glass as illustrated in FIG. 1.
In this type lighting discharge lamp, an emission space-surrounding portion of the order of 2 cc is defined in the center of the light-emitting tube 10. Within this emission space-surrounding portion, a pair of electrodes 21,22 are disposed in an opposing relation. The electrode interval is at most 10 mm, for, example, about 7 mm. Discharge of an arc takes place between the pair of electrodes 21,22 during operation to emit light. Numerals 31,32 indicate bases.
Mercury is an essential component for retaining the discharge of the arc and their sealed amounts are suitably selected. As exemplary rare gases employed in this invention, may be mentioned xenon and argon.
It is desirable that a halogen and lutetium should be sealed in the form of lutetium halide. Described specifically, lutetium iodide, lutetium bromide and the like include.
It is necessary in this invention that the amount of lutetium sealed within the light-emitting tube falls in a range of from 2 x 10⁻⁷ mol/cc to 2 x 10⁻⁵ mol/cc. So long as the sealed amount of lutetium is inside the above range, as will be understood from the description of below-mentioned Experimental Examples, the premature clouding of the light-emitting tube is avoided effectively to enhance its luminous flux utilization and the variations of its color temperature depending on those of supply power for operation are reduced to a small extent.
In this invention, an alkali metal such as lithium, sodium, potassium, rubidium or cesium may be addionally sealed within the light-emitting tube, for example, in order to stabilize arc discharge.
Experimental Examples, which were performed with a view toward supporting the effects of this invention, will hereinafter be described.

[Experimental Example 1]

Lighting discharge lamps in which a halogen and lutetium in various amounts were sealed together with mercury and a rare gas (argon) within a light-emitting tube were actually fabricated by way of trial. The thus-fabricated discharge lamps were lighted at the rated power consumption to investigate the relation between the sealed amount of lutetium and the luminous efficiency.
Incidentally, each light-emitting tube had an internal volume of 2 cc, the electrode interval was 7 mm and the rated power consumption of each lighting discharge lamp was 575 W. The lutetium was sealed in the form of lutetium iodide (LuI₃)
Results in the present Experimental Example 1 are illustrated in FIG. 2. It was confirmed that the luminous efficiency is maintained to at least 60 lm/W so long as the sealed amount of lutetium falls within a range of 2 x 10⁻⁷ mol/cc - 2 x 10⁻⁵ mol/cc. Namely, when the sealed amount of lutetium exceeds the upper limit of the above range, light emitted is remarkably absorbed in halogen vapor outside the arc. On the other hand, any amounts less than the lower limit of the above range will result in predominant light emission caused by mercury. Any amounts outside the above range will hence lead to decreased luminous efficiency.

[Experimental Example 2]

A lighting discharge lamp was fabricated by way of trial in the same manner as in Experimental Example 1 except that the sealed amount of lutetium was changed to 3 x 10⁻⁶ mol/cc. The this-fabricated discharge lamp was lighted at its rated power consumption. As a result, its color temperature and luminous efficiency were found to be about 5500 K and 85 lm/W respectively.
The spectral distribution of the lighting discharge lamp in the present Experimental Example 2 is illustrated in FIG. 3. As is understood from the drawing, light emission caused by lutetium was continuously observed throughout the wavelength region of visible rays. It was hence confirmed that the lighting discharge lamp has a luminous distribution suitable for lighting discharge lamps.

[Experimental Example 3]

A lighting discharge lamp was fabricated by way of trial in the same manner as in Experimental Example 1 except that the sealed amount of lutetium was changed to 3 x 10⁻⁶ mol/cc. The thus-fabricated discharge lamp was lighted at its rated power consumption to investigate the variations of its color temperature as the operation time went on.
In FIG. 4, a curve A indicates a result of the present Experimental Example 3. I was confirmed therefrom that variations of its color temperature are scarcely observed even when 800 hours pass since the lamp has been lighted.
On the other hand, the same experiment as described above was conducted on a short-arc metal halide lamp in which dysprosium and holmium were sealed in a total amount of 3 x 10⁻⁶ mol/cc instead of lutetium. As shown by a curve a in FIG. 4, its color temperature gradually lowered as the operation time went on. Upon elapsed time of about 800 hours after the lighting, its color temperature decreased by a degree as great as about 1,000 K.

[Experimental Example 4]

A lighting discharge lamp according to this invention was fabricated by way of trial in the same manner as in Experimental Example 3 to investigate the variations of its color temperature as supply power for operation was changed.
In FIG. 5, a curve B indicates results of the present Experimental Example 4. It was confirmed therefrom that variations of its color temperature are a little even when the supply power for operation was changed to a considerable extent.

[Experimental Example 5]

A lighting discharge lamp according to this invention was fabricated by way of trial in the same manner as in Experimental Example 3 except that lutetium iodide (LuI₃) was changed to lutetium bromide (LuBr₃) to investigate the variations of its color temperature as supply power for operation was changed.
In FIG. 5, a curve C indicates results of the present Experimental Example 5. It was confirmed therefrom that although this lamp is somewhat inferior to that (the curve B) in Experimental Example 4 in which lutetium iodide (LuI₃) was used, the variations of its color temperature are reduced to a sufficiently small extent so long as it is used at a power consumption of at least 400 W.
Data obtained by conducting an experiment in which the same short-arc metal halide lamp with dysprosium and holmium sealed therein as the convenional metal halide lamp in Experimental Example 3 was used and it was operated at varied power consumptions are shown by a curve D in FIG. 5.

[Experimental Example 6]

Lighting discharge lamps were separately fabricated by way of trial in the same manner as in Experimental Example 3. The thus-fabricated lighting discharge lamps were subjected to a continuous lighting test to investigate whether their light-emitting tube became cloudy.
With respect to the conventional short-arc metal halide lamp, the clouding of its light-emitting tube considerably proceeded in 100-200 hours. With respect to the lighting discharge lamp according to this invention on the other hand, the clouding of its light-emitting tube was not observed even when the operation was conducted for a long period of time beyond 200 hours. It was hence confirmed that the lighting discharge lamp according to this invention is sufficiently high in luminous flux utilization.

[Example 7]

Based on the structure illustrated in FIG. 1, lighting discharge lamps were fabricated by sealing respectively DyI₃, HoI₃, CeI₃, ErI₃, GdI₃, LuI₃, SmI₃, TbI₃, NdI₃ and PrI₃ within their light-emitting tubes. These lamps were lighted at the rated power consumption to observe conditions of the clouding in their light-emitting tubes upon elapsed time of 100 hours after the lighting. Results are shown in Table 1. Table 1

Rare earth halide Evaluation Rare earth halide Evaluation

DyI₃ B LuI₃ C

HoI₃ A SmI₃ A

CeI₃ B TbI₃ B

ErI₃ A NdI₃ A

GdI₃ A PrI₃ B
In Table 1, the meanings of "A", "B" and "C" are as follows:

A: The light-emitting tube becomes significantly cloudy and both electrodes cannot be seen;
B: The light-emitting tube becomes slightly cloudy and both electrodes can be seen; and
C: The light-emitting tube remains clear.

It was found from the results of Table 1 that LuI₃ (lutetium iodide) is inhibited in reaction with the light-emitting tube.

Claims

1. In a lighting discharge lamp comprising a light-emitting tube in which a halogen and lutetium are sealed together with mercury and a rare gas, the improvement wherein the sealed amount of lutetium falls in a range of from 2 x 10⁻⁷ mol/cc to 2 x 10⁻⁵ mol/cc.

2. The lighting discharge lamp as claimed in Claim 1, the halogen and lutetium are sealed in the form of lutetium iodide.

3. The lighting discharge lamp as claimed in Claim 1, the halogen and lutetium are sealed in the form of lutetium bromide.

4. The lighting discharge lamp as claimed in Claim 1, an alkali metal is additionally sealed.

5. The lighting discharge lamp as claimed in Claim 1, an interval between both electrodes is at most 10 mm.