The Kolorlux lamp (high pressure Mercury), shown in Figure 9.4, was one of the first HID lamp types to appear on the market in 1930s. The outer bulb stabilises and maintains the necessary high temperature around the arc tube and also absorbs the potentially hazardous UV radiation coming from the arc. Nitrogen gas within the outer bulb protects the metal parts from oxidation. The bulb is phosphor coated to generate some red light that is added to the light from the arc tube, improving the colour rendering and appearance of the lamp. The light direct from the arc is mainly blue and green.

Figure 9.4. Kolorlux lamp construction.

Inside the arc tube the starting gas is Argon. See Figure 9.5. Mercury ions support the arc after the lamp starts. The main electrodes are double layers of tungsten wire with rare earth oxides for long life and good lumen maintenance. The starting resistor limits the current to a low value for starting. After the lamp starts the current bypasses the resistor and starting electrode as soon as the resistance between the main electrodes fails to below that of the starting resistor.

Figure 9.5. Kolorlux lamp starting system.

Kolorlux lamps offer distinct advantages over incandescent lamps - see Figure 9.6.

• High lumen output per watt
• Cool colour appearance
• Long life
• Low operating cost