The light of discharge lamps is generated by sending an electrical discharge through an ionised gas or metal vapour. Low-pressure discharge lamps like fluorescent lamps, or high-pressure discharge lamps like metal halid lamps accordingly have low or high operating pressure inside the discharge lamp. As halogen metal halide lamps offer good luminous efficacy and colour rendering properties combined with a compact size, a long life and low power consumption they are not only ideally suited for outdoor illumination. They are nowadays also increasingly deployed in commercial and private spaces.