Metal halide lighting with good color during dimming may be obtained. An
appropriate balance of commonly used metal halides (NaI, DyI.sub.3,
CeI.sub.3, CaI.sub.2, TlI) is dosed in the lamp. No mercury is used. A
higher than typical xenon fill pressure from 50 to 500 Kilopascals may be
used to help control thermal properties and voltage. If necessary,
modulation of the power at acoustic resonance frequencies may be used to
straighten and center the arc. Efficient and pleasant white output is
obtained. As the power is reduced, the chromaticity either (1) remains
fairly constant or (2) drifts acceptably towards warm pinkish colors.
Large factors of attenuation in output can be realized. The lumen output
was reduced by at least a factor of twenty in one sample as the power was
dimmed from 70 to 20 watts.