An arc lamp assembly which includes in combination a reflector and a light source which is surrounded by said reflector. A dichroic coating on the reflector functions to reflect radiation in the range of about 300 to 600 nm. The light source is an arc lamp which contains a metal halide fill component which includes a mixture of scandium iodide, or other suitable lanthanide, indium iodide and cesium iodide, whereby the lamp assembly emits effective amounts of UV radiation to cure selected chemical compositions. The fill mixture, which contains no sodium component, contributes to improved lamp life and a reduction in passive lamp failure over halide fill mixtures which contain sodium iodide as a fill component.