Metal Halide Lamps
Metal Halide lamps are a member of HID lamps family and known as compact, powerful, efficient light source due to its high light beam output compared to its size. Metal halide lamps were developed as a way of improving the performance of high pressure mercury lamps in terms of their colour appearance and light output. They work by introducing the salts of other metals into the arc tube. As each element has its own characteristic spectral line, by adding a mixture of different elements into the discharge it is possible to create a light source with good colour rendering in a variety of colours. There are a lot of problems with introducing new elements into a discharge. First, the element must be volatile and secondly it should not chemically attack the arc tube. To avoid these problems it has become common practice to introduce metals into the lamp as metal halides. Metal halides are generally more volatile than the metals themselves and the metal halides do not attack the arc tube. The metal halide compound breaks up into the metal and halogen ions at the high temperatures in the centre of the discharge and reforms at the lower temperatures near the wall of the tube. As shown in the picture of HP-mercury vapor lamp’s post, there are few changes seen in the structure but the main change is the arc tube size highly reduced.
It can be informed that general structure of MHL same as HID lamps. On the other hand, arc tube contains argon and mercury gas mixture in it but it is reached with halide metal salts. Due to argon’s property, it facilitates striking arc across the two electrodes when potantial different applied on lamps tips. The arc vaporizes mercury and halide that produce light as temperature and pressure increases.