High-pressure mercury-vapor discharge lamp having a light output with incandescent characteristics

Abstract

The light output of a high-presure discharge lamp that employs a mercury arc tube is selectively modified by two luminescent coatings on the inner surface of the outer protective envelope to provide color rendering and a source-color that are similar to those of an incandescent-type lamp. The coating in contact with the envelope surface comprises a blend of two selected phosphors -- one which absorbs and is excited by blue-violet radiations produced by the arc discharge and emits in the green portion of the spectrum, and another which also absorbs and is excited by the blue-violet radiations and by yellow radiations produced by the discharge and emits in the red portion of the spectrum. The second luminescent coating facing the arc tube comprises a phosphor that absorbs ultraviolet radiations produced by the mercury discharge and converts them into red radiations. The ultraviolet-converting phosphor coating is such that it transmits blue-violet and yellow radiations generated by the arc tube so that they can be absorbed and converted by the first phosphor coating. The desired color-rendering characteristics and reduction in the color temperature of the light emission are achieved with a minimum drop in light output and efficacy by using a mixture of green-emitting CaS:Ce phosphor and red-emitting CaS:Eu phosphor as the first-applied coating, and europium-activated yttrium vanadate phosphate phosphor as the second coating. Various other combinations of phosphors for the two luminescent coatings are also disclosed.

Dependencies are inferred from the claim text.