Fluorescent lamp using high performance phosphor blend which is protected from color shifts by a very thin overcoat of stable phosphor of similar chromaticity

摘要

Fluorescent lamps have a predetermined correlated color temperature and a combined efficiency and good color rendition of illuminated objects. The lamps utilize a two-layer phosphor coating comprising a layer coated onto the envelope interior surface and formed of a very high performance three-component blend which includes a blue-emitting phosphor, a green-emitting manganese-activated zinc silicate phosphor, and a red-orange emitting phosphor, all mixed in predetermined amounts and relative proportions to provide an emission of approximate predetermined x-y coordinates. Under some conditions, the phosphor blend when used as a single layer is subject to depreciation of the light output of the green component, particularly in the vicinity of the lamp electrodes which results in color shifts which are objectionable from an aesthetic standpoint. To protect the green-emitting component of the high performance blend, there is provided over the phosphor blend layer a very thin layer of finely divided phosphor which is very stable and which has an emission of approximately the same x-y coordinates as the high performance phosphor blend layer. The resulting lamp has overall improved performance from an aesthetic standpoint.