Metal Halide Lamp :
Metal Halide Lamps Working and Construction
- This lamp is known as mercury halide or metal halide lamp. It has a short arc tube. Inside it there are series of lamps combined within a single arc-tube with output characteristics of different mixtures of elements.
- When such metals (like thallium, indium, sodium, dysprosium) are introduced into mercury arc tube, the mercury spectrum is suppressed reducing the ultraviolet radiation but added metal atoms partly compensate by causing a wide range of spectral bonds to be emitted.
- It is possible to produce white or green light. If the metals are used in the element form they attack the discharge tube.
- To avoid this instead of metals in element form its halide is used like iodide i.e. sodium iodide. The lamps require high starting voltage.
- This is provided by ignitor as shown connector in the Figure. Ignitor is connected across the lamp terminals. This type of starter (ignitor) enables the lamp to be restruck within a minute of being switched off.
- More pure white light is obtained.
- More energy efficient than mercury lamp, halogen lamp.
- Good for high ceiling indoor lighting.
- Cost is more.
- Produces more light pollution.
- Used for high bay interior and high mast exterior installations.
- Sport stadium where coloured T.V. transmission is expected.
- Flood lighting projectors.