here ya go.. a little reading on that subject for ya.
HQI= mercury quartz iodide. ( also seen as Halogon qartz iodide)the H comes from the Hg which is the symble for mercury pnthe per. chart. this type of bulb is a HID bulb , ( High intensity discharge) it actaully uses a powerful arc through a gas to give off the light
this is just atype of MH