The development of the metal halide lamp is a real success story. The improvements of recent years such as higher colour stability and colour rendition or electronic control gear allow them to be used in demanding architectural lighting applications. They are extremely energy-efficient, have a long service life and constitute a brilliant, virtually point-form light source. The latest advancements like the miniaturisation with the 20W lamp and the development of dimmable systems are starting to find their way into practical designs with ERCO lighting tools.