What about a single metal halide light . I think you can get them down to 75w now and i think that arcadia do them but iam not sure , hope this can help . Something to look into though .
You could check this out depending on the size of your tank, i dont know if this would give you enough wattage, but these look interesting for a nano tank, although they come supplied with an origional lamp which is a drawback IMO, its only new on the market as far as i know. But a good price if it worked for you.