Patent Application
20060186785
The present invention is directed to method of improving lumen maintenance of an electrodeless lamp and to an electrodeless lamp with improved lumen maintenance. Electrodeless lamps are disclosed in U.S. Pat. Nos. 5,834,905 and 6,777,867.
Lumen maintenance is a ratio, expressed as a percentage, of (i) lamp lumens output at a predetermined number of lamp operating hours to (ii) lamp lumens output at a reference number of lamp operating hours (typically 100 hours). For example, the Icetron™ lamp sold by OSRAM SYLVANIA (generally described in the above-noted U.S. Pat. No. 6,777,867 and shown in
Of particular interest in the present application is the decline of lumen maintenance when the electrodeless lamp is operated in a cold environment, for example when the bulb wall temperature of the lamp is 35° C. or lower. It has been found that some electrodeless lamps have detectably lower lumen maintenance when operated at a low temperature compared to electrodeless lamps operated at a normal ambient temperature. When an electrodeless lamp is operated at room temperature (normal ambient), the bulb wall temperature of the lamp typically is 70° to 80° C. and can reach 110° C. in an enclosed fixture. By contrast, when an electrodeless lamp is operated outdoors in a cold environment, the bulb wall temperature may be 35° C. or lower. Lamp operation in the cold environment has been found to reduce lumen maintenance below the rated amount.
An object of the present invention is to provide a novel method of improving low temperature lumen maintenance of an electrodeless lamp whose glass body has an interior surface with red and green emitting phosphors thereon, where the method includes coating the red emitting phosphors and/or the green emitting phosphors with an aluminum-containing coating to thereby increase the low temperature lumen maintenance of the lamp, where the low temperature lumen maintenance is a ratio of (a) lamp lumens at a first number of lamp operating hours to (b) lamp lumens at a reference number of lamp operating hours, when the lamp is operated with a bulb wall temperature of 35° C. or lower.
A further object of the present invention is to provide a novel method of increasing low temperature lumen maintenance of an electrodeless lamp whose glass body has an interior surface with red emitting Y2O3:Eu (YOE) phosphors and green emitting (Ce,Tb)MgAl11O19 (CAT) phosphors thereon, in which an aluminum-containing coating of aluminum oxide or aluminum oxynitride is coated directly on the CAT phosphors and/or the YOE phosphors (preferably at least the CAT phosphors) to increase low temperature lumen maintenance.
A yet further object of the present invention is to provide a novel electrodeless lamp that includes a glass body containing a medium that generates UV radiation, where the glass body has an inner surface with red emitting Y2O3:Eu (YOE) phosphors and green emitting (Ce,Tb)MgAl11O19 (CAT) phosphors thereon, the YOE and CAT phosphors emitting light when excited by the UV radiation in the absence of an electrode, and where the YOE and/or the CAT phosphors (preferably the CAT phosphors) are coated with an aluminum-containing coating to thereby improve the low temperature lumen maintenance of the lamp. The interior surface of the glass body may also have blue emitting BaMgAl11O17:Eu (BAM) phosphors thereon.
These and other objects and advantages of the invention will be apparent to those of skill in the art of the present invention after consideration of the following drawings and description of preferred embodiments.
a and 1b are side and top views of an electrodeless lamp of the prior art.
An electrodeless lamp of the prior art shown in
In the invention, the low temperature lumen maintenance of an electrodeless lamp such as described above and whose glass body has an interior surface with red and green emitting phosphors thereon is improved by coating the red emitting phosphors and/or the green emitting phosphors with an aluminum-containing coating to thereby increase the low temperature lumen maintenance of the lamp. The aluminum-containing coating is coated directly on the respective phosphor particles, such as shown in
The low temperature lumen maintenance is the above-described ratio of (a) lamp lumens at a predetermined number of lamp operating hours to (b) lamp lumens at a reference number of lamp operating hours, when the lamp is operated with a bulb wall temperature of 35° C. or lower.
In a preferred embodiment, the red emitting phosphors are YOE and the green emitting phosphors are CAT and the aluminum-containing coating is an aluminum oxide coating that is coated directly on either the YOE phosphors or the CAT phosphors, or both. Low temperature lumen maintenance is improved most by coating the alumina directly on the CAT phosphors and may be yet further improved by coating the alumina directly on the YOE phosphors as well. The alumina coating may be applied in accordance with the process described in U.S. Pat. No. 4,585,673. The aluminum-containing coating also may be aluminum oxynitride.
The phosphors on the interior surface of the glass body may also include blue emitting phosphors such as BAM. Oxidation of Eu2+ to Eu3+ in BAM adversely affects the blue emission of the BAM. The conventional process (e.g., described in the above-noted U.S. Pat. No. 4,585,673) for coating phosphors oxidizes the Eu2+ to Eu3+ and thus BAM phosphors in the electrodeless lamp are not coated when this conventional coating process is to be used.
By way of further explanation, tests have shown that coating the CAT phosphors with the alumina coating provides a significant improvement in low temperature lumen maintenance. A comparison of lamps with uncoated and coated CAT phosphors, with high (about 110° C.) and low (less than about 35° C.) bulb wall temperatures, revealed an improvement in lumen maintenance at the low bulb wall temperatures from 81% to 88% when the coated CAT phosphors were used. Similar tests for coated YOE revealed a less significant improvement, but an improvement nonetheless.
The electrodeless lamp of the invention includes a glass body 10 containing a medium 14 (
While embodiments of the present invention have been described in the foregoing specification and drawings, it is to be understood that the present invention is defined by the following claims when read in light of the specification and drawings.
