Electric lamp and discharge devices – With gas or vapor – Having a particular total or partial pressure
Patent
1995-12-14
1997-11-25
Patel, Nimeshkumar
Electric lamp and discharge devices
With gas or vapor
Having a particular total or partial pressure
313620, 313637, 313641, 313638, 313639, H01J 6112
Patent
active
056916019
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention is based on a metal-halide discharge lamp which can be used for instance for video projection, endoscopy, or medical practice (operating room lights), and which is especially suitable for video projection by the liquid crystal technique (LCD), and especially also for large television screens with an aspect ratio of 16 to 9. Typical power ratings are from 100 to 500 W.
BACKGROUND
The use of aluminum in the discharge vessel of lamps has already been known for a long time. However, it is problematic, in view of the hygroscopic performance of the aluminum compound in the filling process and the severe attack on the electrodes during the service life, which greatly limits the service life. Accordingly, the use of fillings that contain aluminum has until now been limited to either electrodeless lamps (U.S. Pat. Nos. 4,672,267 or 4,591,759, for example) or lamps in which the electrodes are especially coated in order to attain a suitable chemical reaction of the aluminum, see U.S. Pat. No. 3,914,636, to which German Patent Disclosure DE-OS 24 22 576 corresponds.
A metal-halide lamp with wall loading of more than 40 W/cm.sup.2 is known, in which a filling that contains either aluminum chloride or aluminum bromide is introduced into a discharge vessel that has activated electrodes, see German Patent 1,539,516. However, such fillings tend to make for very short service lives, on the order of magnitude of 100 hours. They are intended to generate a daylight-like spectrum, at the cost of high loading.
U.S. Pat. No. 5,220,237, Maseki et al., to which European Patent Disclosure EP-A 459 786 corresponds, describes a lamp for photooptical purposes with a long service life, particularly for video projection, which as filling components contains in addition to mercury and argon iodides of the rare earths dysprosium and neodymium and of cesium. Rare earth fillings were previously the only ones that were usual for such lamps, because they assure good color rendition with a high light yield. This patent disclosure is hereby expressly incorporated by reference.
Although for general lighting rare earth fillings are quite suitable, they do not meet the high demands made of lighting for photooptical purposes. The reason for this is that large quantities of rare earth metals attack the discharge vessel, which is typically of quartz glass, and at the high operating temperatures this gradually leads to devitrification and finally to the risk of bursting. The devitrification worsens the optical characteristics of such lamps so considerably (diffuse projection of the arc) that the lamps can no longer be used for photooptical purposes, where exact projection of the arc by the optical system is critical. Finally, maintenance of these lamps is also unsatisfactory. The light formation with rare earth metals also results primarily from molecular electron transitions which thus occur at the edge of the arc, so that in the application for projection purposes, for instance, color fringes can appear on the projection screen (poor color uniformity).
THE INVENTION
It is an object of the present invention to create a lamp for photooptical purposes that is distinguished especially by a long service life, good maintenance, and homogeneous color distribution, and which has good color rendition.
Briefly, in accordance with the invention, metal-halide lamps for photo-optical purposes provide a color temperature of 5000 K and have the combination of these features: an electrode spacing of 15 mm at most; to create the most pinpoint possible light source, preferred values are between 2 and 8 mm. The color temperature is above 5000 K, and in particular is from 6000 to 10,000 K; and
The lamp was a filling that, as its essential or sole metal-halide component, contains from 0.1 to 4.5 mg/cm.sup.3 of AlI.sub.3. Adding aluminum in this form to the lamp with the aforementioned small electrode spacing has two advantages. First, accurate metering of even small quantities of aluminum is possible, since the atomic weight of
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Barthelmes Clemens
Dittrich Thomas
Frey Anna-Maria
Maier Jurgen
Pilsak Manfred
Patel Nimeshkumar
Patent-Treuhand-Gesellschaft F. Elektrische Gluehlampen mbH
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