Hi,
HQL is not the best choice. HQL bulbs do contain Hg as the only component of metal vapour and hence need fluorescent coating of the glass to produce visible light. This results in quite a loss of intensity and also only allows a discontinuous spectrum with larger gaps between narrow emission peaks. So their light efficiency is limited to like 40-50 lm/W and their colour rendering poor. Due to their significan heat emission still a meaningful light source to use for a basking spot also, quite surprisingly, many reptiles do love them), but not a good choice for the only representation of sunlight in a tank. A metal halide where the Hg is supplemented by carefully selected metal iodides (and/or -bromides)like for the Osram HQI or better HCI or Philliops CDM types (sorry, do not knowe much about respective US brands and names) is much, MUCH better. Due to the high light efficiency (80-100lm/W) these lamps do produce much less heat per watt than all other light sources. So overheating is definitely not a problem. (for the fishh keepers heat in fact may matter, if they replace 80 W of fluorescent lighting by 150 W metal halide....but thats a different story...also take care not to buy the 10 000 K bulbs, coral keepers use) In contrast, you often have to supplement these lights by eg halogen bulbs to reach the desired basking temp.
In Europe, since a couple of years these type of bulbs have become the gold standard for lighting in the enclosures of diurnal reptiles. Today, already a lot of experience has accumulated regarding their usefulness, effects on reptile behaviour an health and people still are very enthusiastic about them. Only by using these bulbs you can implement basking spots at about 100 000 Lux which equals the brightness, even heliophile herps do experience in their natural habitat.
Since the advantages are that obvious, the experiences that plentiful and good and especially for chameleons, Uromastyx, Pogona, north american desert iguanids, lacertids and you name it , the differences in behaviour, colour and health are clearly visible, I am always surprised to hear that these bulbs are still not widely used for herpetoculture in the US.
Maybe this is relaed to the fact that US herpers for waht reasons ever tend to ignore or not read european -and especially german- papers on herpetoculture
Its more than wort the try, believe me.
If you have doubts, lokk at the respective spectra, light yields and overall intensities. Nothing better on the market today (but I am still waiting for the sulfur vapour lamps to come.. 
)
Best regards
Ingo
