HQI is s type of metal halide bulb, it was a proprietary brand name but has now come to mean any double ended MH bulb. For a given wattage, the bulbs burn brighter with a cleaner color spectrum and allegedly last longer. They require special ballast; usually an electronic one is specified but is not required. Used in Europe for many years. Bulb selection for planted aquaria is limited, AB has a 5.5K in 150W and 250W. Most any Reef based vendor will have pictures of the bulbs,. Here is a link. http://www.premiumaquatics.com/Merc...&Product_Code=10K-150HQI&Category_Code=Hbulbs
Been running on this for some a month or two now, and I'm not really that happy about it. It packs quite a punch, but color are very limited. My L. Repens has always been looking incredibly red and nice, but now it's now showing the same color. This might be another issue in your contry, but here in norway, color selection is to small...
One lesson I learned the hard way, when choosing your MH setup, go with whatever offers the largest variety of bulbs, spectrums and kelvin ratings. Many regular MH bulbs appear too green/yellow but there are many out there that are great performers. Balancing them with some flourescents however is quite common, that's what I'll be doing with my next MH fixture.
HQIs are great because they fit in a very small space compared to the huge mogul thread bulbs.
I'm very happy with the looks and performance of the Aqua-Medic aquaspacelight fixture I have. I talked my lfs to being competitive with mail order prices and swapping out the normally supplied reef type lighting to something more plant friendly.
PFO builds a very nice fixture and it can be had in many variations, they are built for you on order.
Sunlight supply is about to relase a new line of MH fixtures.
There are others.
There are a lot of reviews in the Vendor Forum of Reef Central. Keep in mind you probably do not want the 10K+ bulbs normally listed with fixtures.
If you are a DIY guy, MH will cost you less than PC (bulbs excluded). I picked up a 250W MH pendant for $20 on eBay, and the guy had about 50 of them for sale. They were pulled from a shopping mall, I pulled it apart, separated the ballast, reused reflector, mogul socket and UV glass and it's ready to light my new reef tank. Also picked up some spare ballasts on ebay for around $15 each. Bubls on the other hand were between $50-100 each.