Medium / high pressure lamps

These lamps are also referred to as HID (high intensity discharge) lamps. They produce much more light per unit of lamp volume than low pressure lamps.

Medium / high pressure lamps have tungsten electrodes that are not preheated as in low pressure lamps. Ignition voltages of several Kilovolts are required to start the lamps. HID lamps have generally an arc tube and an outer envelope, which protects the arc tube and provides the proper thermal environment for the arc tube and blocks the UV.

One type is the MH (Metal Halide) lamp. It produces almost white light by a high pressure mixture of mercury, argon and metal halides in the arc tube. The arc tube can be made of quarz or alumina and is small (5cm for 400W) compared to other lamp types. The latter one is referred to as Ceramic Metal Halide and has better color rendering than the quarz MH lamp. The luminous efficacy of MH lamps is up to 115 lm/W.

Another one is the High Pressure Sodium (HPS) lamp that produce a yellowish light due to the sodium in the alumina arc tube. Its arc tube is somewhat longer (10-20cm for 400-1000W) than for MH lamps. They are mainly used for street lighting and horticultural lighting (photosynthesis) and have a luminous efficacy of 150 lm/W.

For UV applications medium pressure mercury lamps are made in lengths up to several meters and powers up to several tens of Kilowatts.

Lamp life for HID lamps and color rendering for MH lamps in particular depends greatly on lamp usage (number of starts) and the ballast performance. The high frequency lamp drivers from Nedap Light controls offer significant better performance than standard low frequency ballasts. They are available in 320 to 400W for metal halide lamps, 600-1000W for HPS lamps and 400W to 48kW for medium pressure UV lamps.