3. Content 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.

4. High Intensity Discharge Lamps Mercury Vapour High Pressure Sodium Vapour Metal Halide

5. Mercury Vapour Requires a ballast to limit running current External Internal Starting is achieved buy a auxiliary electrode and resistor in the lamp

6. External Ballasted HPMV Auxiliary electrode Resistor

7. 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

8. High Pressure Sodium Vapour 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

9. High Pressure Sodium Vapour 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 Broadening 1100°C slightly less than 1 atmosphere Near the end of their life exhibit a phenomenon known as cycling

10. Metal Halide Quartz discharge tube containing high-pressure mercury Sodium halide Scandium halides Argon is used to aid ignition.