To achieve warm-white luminous colors, metal halide discharge lamps generally contain tin iodide. However, this also requires accurate dosing with metallic tin. As a fill in the discharge vessel, the lamp often includes, in addition to mercury and a noble gas, metal iodides and metal bromides of sodium, tin, thallium, indium and lithium. Tin-containing fills of this type often have a luminous flux which is too low and lead to electrode corrosion and electrode burn-back. Tin-containing fills of this type therefore require special electrodes which are able to withstand this particularly aggressive fill, cf. for example U.S. Pat. No. 4,782,266. When producing lamps of this type, this entails longer changeover times when changing lamp type and therefore involves high storage costs.
Furthermore, U.S. Pat. No. 5,694,002 has disclosed a lamp which contains a metal halide fill comprising the metals Na, Sc, Li, Dy and Tl, with a warm-white luminous color. The color temperature is 3000 K.
Scandium-containing fills of this type have a very poor maintenance, which means that the luminous flux drops considerably during the operating time. Moreover, the color rendering of scandium-based lamps is relatively poor.
US-A 2004253897 has disclosed a metal halide lamp with a two-ended outer bulb which surrounds only part of the discharge vessel.
USPTO Backgrounds
USPTO Backgrounds