Variable color temperature fluorescent lamp

Color temperature change in a mercury-rare gas low pressure discharge has b een investigated. Different pulse waveforms have been employed to increase the ratio of mercury upper level transitions with respect to the resonant 2 54 nm radiation. Low pressure fluorescent light sources were made with coat ings consisting of a blue phosphor, sensitive to 365 nm ultraviolet radiati on, blended with the standard 254 nm excited red/green phosphors. With a fa st rise excitation waveform, a color temperature rise of as much as 1700 K was realized although at a cost of 26% in relative luminous efficacy. An im proved scheme for greater color temperature change is proposed based on a p hosphor that is excitable by the mercury 185 nm ultraviolet radiation but w hich does not absorb 254 nm radiation. (C) 2000 American Institute of Physi cs. [S0021-8979(00)04209-2].