Electric lamp and discharge devices – With temperature modifier – For filament or heated cathode
Patent
1989-04-11
1990-11-20
O'Shea, Sandra L.
Electric lamp and discharge devices
With temperature modifier
For filament or heated cathode
313491, 313632, H01J 1706, H01J 6152
Patent
active
049721151
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a hot-cathode type low-pressure rare gas discharge lamp comprising electrodes at least one of which operates as a hot cathode during operation of the lamp
BACKGROUND OF THE INVENTION
A discharge lamp for use as a light source for office automation equipment is keenly required to have a uniform luminance over the entire length thereof.
As a prior art relating to improvements of the luminance distribution of the discharge lamp, for instance, Japanese Patent Application Laid-Open (KOKAI) No. 57-11465 (1982) discloses a system in which electrode filament coils are heated into white-incandescence to emit light, thereby compensating for the reduction in luminance which would tend to occur particularly at end portions of the lamp.
In the above-mentioned prior art, however, it is necessary to heat the electrode filaments to a color temperature of 2600.degree. to 3200.degree. K, and, therefore, it is necessary to provide another pair of filament coils for maintaining the life of the lamp, namely, for maintaining the discharge under the heated conditions. Accordingly, the prior art involves an increase in the number of component parts of electrode structure, with the result of a very complicated electrode structure, leading to a complicated manufacturing process and a rise in cost.
DISCLOSURE OF THE INVENTION
It is an object of this invention to provide a hot-cathode type low-pressure rare gas discharge lamp which can prevent the life thereof from shortening, with a non-complicated ordinary electrode structure, can obtain a luminance distribution over the nearly entire length thereof satisfactory for practical use of the lamp as a light source for office automation equipment, and can realize enhanced luminance distribution characteristics.
For attaining the above object, the hot-cathode type low-pressure rare gas discharge lamp according to this invention is characterized in that at least one of electrodes provided at both ends of a glass bulb is heated to a temperature of 800.degree. to 1200.degree. C.
The hot-cathode type low-pressure rare gas discharge lamp of this invention, in which at least one of the electrodes is heated to not lower than 800.degree. C during lighting, is different from a general discharge lamp filled with mercury, in that a favorable discharge condition is obtained between the electrodes provided at both ends of the glass bulb and, in addition, the upper limit of the heating temperature is set to not more than 1200.degree. C., whereby the life of the lamp is securely prevented from shortening. The improvement in luminance distribution and the effect on the life, as mentioned above, have been confirmed by experimental data.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a partially cutaway front view of a hot-cathode type low-pressure rare gas discharge lamp according to one embodiment of this invention;
FIG. 2 is a characteristic chart showing the luminance distribution of a mercury vapor lamp;
FIG. 3 is a characteristic chart showing the luminance distribution of the lamp according to this invention;
FIG. 4 is a characteristic chart showing the relationship between filament temperature and lamp life; and
FIG. 5 is a characteristic chart showing the luminance distribution of a lamp when the lamp is lighted by a direct current.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a partially cutaway view of a hot-cathode type low-pressure rare gas discharge lamp provided with an aperture window portion, according to this invention. In the figure, numeral 1 denotes a glass bulb 15.4 mm in outside diameter and 0.7 mm in wall thickness, and a reflection film 2 is provided on the inner peripheral surface of the bulb 1.
The reflection film 2 is coated with a phosphor layer 3, which comprises a green phosphor GP.sub.1 G.sub.1, a product by Kasei Optonix, Ltd.
At a common portion of the phosphor layer 3 and the reflection film 2 which extends in the longitudinal direction of the bulb 1, an aperture window portion 8 having a width of 2 mm
REFERENCES:
patent: 4117374 (1978-09-01), Witting
patent: 4329622 (1982-05-01), Corona et al.
Adachi Hiromi
Kamano Yujiro
Kobayashi Toshihiko
Mitsuhashi Seishiro
Murakami Katsuo
Mitsubishi Denki & Kabushiki Kaisha
O'Shea Sandra L.
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