High-intensity discharge lamp

Construction and Types of HID Lamps

• HID lamps utilize various types of chemistry in their arc tubes, including mercury-vapor, metal-halide, ceramic metal-halide, sodium-vapor, and xenon short-arc lamps.
• The light-producing element in HID lamps is a stabilized arc discharge within a refractory envelope arc tube.
• Mercury-vapor lamps were the first commercially available HID lamps, while metal-halide and ceramic metal-halide lamps produce neutral white light, and low-pressure sodium-vapor lamps are highly efficient.

Radioactive Substances in HID Lamps

• Some HID lamps incorporate radioactive substances like krypton-85 and thorium to aid in starting the lamps and improving their operating characteristics.
• Krypton-85 is mixed with argon in the arc tube, while thorium is used in the electrodes to produce ionizing radiation within the lamp.

Applications and Uses of HID Lamps

• HID lamps are commonly used for high light levels over large areas, such as in gymnasiums, stadiums, roadways, and parking lots.
• They find applications in indoor gardening, aquarium lighting, automotive headlamps, and aircraft lighting.
• HID lamps produce UV radiation, necessitating the use of UV-blocking filters in certain applications.

Ballasts and Starting Mechanisms for HID Lamps

• HID lamps require ballasts to start and maintain arcs, with various methods used to strike the arc.
• Ongoing experiments aim to replace toxic mercury in HID lamps, with mercury-vapor lamps initially using a third electrode and other styles employing pulses of high voltage for starting.

End of Life Considerations and Phosphor Coating

• Factors affecting the longevity of HID lamps include wear from on/off cycles, with the highest wear occurring when the burner is ignited while hot.
• The end of life for HID lamps may exhibit a cycling phenomenon due to rising internal gas pressure, with aging indicated by a blue/violet discoloration of the emitted light beam.
• Some HID lamps, like Mercury Vapor lamps, utilize phosphor coatings to absorb UV light emitted by gas atoms and improve color rendering properties.

High-intensity discharge lamp Data Sources