ContentContent• Types of high intensity discharge lights• Colour rendering of high intensity discharge

lights• Operating principles of high intensity

discharge lights• Control equipment associated with high

intensity discharge lights• Efficacy of high intensity discharge lights• Common faults in discharge lights discharge

lamps.

High Intensity Discharge Lamps

•Mercury Vapour•High Pressure Sodium Vapour•Metal Halide

Mercury VapourRequires a ballast to limit running current•External•Internal Starting is achieved buy a auxiliary

electrode and resistor in the lamp

External Ballasted HPMV

Auxiliary electrode

Resistor

Internal Ballasted HPMV

• High-pressure mercury tube in series with a tungsten filament• Runs on mains voltage without additional gear• Combines a continuous spectrum from the incandescent

source and high pressure mercury source

High Pressure Sodium High Pressure Sodium VapourVapour• Requires a Ballast for control of running current• Ignitor to start the arc in the lamp

Some smaller lamps may have an Ignitor incorporated in the lamp

High Pressure Sodium High Pressure Sodium VapourVapour

Contains xenon as well as some mercury

The colour difference between HPS and LPS is due to

• Higher gas pressure• Higher temperature• Addition of mercury

Efficacy 100 lm/W

Arc tube is typically made of translucent sintered aluminium oxide.

Pressure Broadening1100°C

slightly less than 1 atmosphere

Near the end of their life exhibit a phenomenon known as cycling

Metal HalideMetal Halide

Quartz discharge tube containing•high-pressure mercury•Sodium halide•Scandium halidesArgon is used to aid ignition.