You want to keep a mixed reef then... 40g of water isn't a whole lot, so if you stick a metal halide unit over the top of it, it will generate a lot of heat and keep the temp unstable. I like T5HO fixtures and retrofit kits personally. Although, you will have to use higher quality bulbs like that of UVL or ATI. Dixie reef is a pretty good source. I don't think they have anything on lighting just yet.
LED lighting is also a pretty good source of light. They have come a long way in DIY LED reef lighting, as well as fixtures. A good fixture could cost you $500. Like those made by AI, like the Vega.