Warm-white fluorescent lamp having good efficacy and color rendering and using special phosphor blend as separate undercoat

摘要

Special commercially available fluorescent lamps of warm-white correlated color temperature of about 3000° K. have both good coloring index and efficacy. These lamps utilize as the light-emitting component a special three-component phosphor blend having emissions principally confined to the wavelength regions of from 430 nm to 485 nm, from 515 nm to 570 nm, and from 588 nm to 630 nm. This phosphor blend is relatively expensive and to decrease expense, it is known to utilize an undercoat of halophosphate phosphor of the same emission color, which decreases the amount of expensive phosphor required. To provide the dual function of decreasing the amount of expensive phosphor blend and also to screen any possible color shifts which might occur in the high performance phosphor blend, without appreciably affecting overall lamp performance, there is provided a phosphor undercoat of very particular phosphor which not only is less expensive than the three-component blend, but which in itself has both good color rendering properties and efficacy. In this manner, lamp costs are decreased and possible color shifts are screened without materially affecting overall lamp performance.