A metal halide high pressure discharge lamp with warm white colour and high efficacy

A Na, Tl, In, Sn high pressure discharge lamp of warm white colour was developed for an efficient energy utilization in indoor illumination. The lamp is characterised by: (1) low colour temperature (CCT = 3300 K) with good colour rendering (Ra = 85). (2) high luminous efficacy of approx. 90 lm/W, corresponding to the 5- to 6-fold of an incandescent lamp, (3) high life time of approx. 4000 h, corresponding to the 4-fold of an incandescent lamp, (4) arbitrary burning position as with an incandescent lamp. These data were achieved through utilization of strongly pressure broadened line radiation (Na, Tl, In) combined with molecular radiation (SnI, SnBr, HgI, HgBr). The main features of the lamp are discussed, in particular a deviation from local thermal equilibrium in the mantle of the discharge.