An HQI metal halide lamp belongs to the family of metal halide HID lamps. Hydrargyum quartz iodide (HQI) lamps differ from standard metal halide lamps in that they are often smaller and are offered in double ended versions and require a special socket. The gasses and metal halide salts used in HQI and standard metal halide lamps are the same.

Between Metal Halide and Mercury Vapor the higher output is emitted from the Metal Halide lamp.

No, the ballast has to be matched to the lamp. 250 watt ballast, 250 watt lamp. Also be sure to match the lamp type to the proper ballast even though the wattage is the same. HPS ballast to HPS lamp, Metal halide ballast to metal halide lamp and mercury vapour lamp to mercury vapour ballast.

No. The lamp has to match the ballast. The lamp will not ignite if the wrong ballast is used.

K. Hick has written:

'Temperature profiles of the electrodes of single ended metal halide discharge lamp'