I know that you get more out of the spiral bulbs by having them vertical, however this makes for very ugly mounting for the most part. It would be much nicer making a hood that has horizontal orientation. I was thinking of making a 4 bulb fixture for my 20g long high light tank. The bulbs would be horizontal and placed in a wooden hood like so:
except I would line it with aluminum tape for better reflection.
As long as the 4 bulbs could still achieve as much par as 3 vertical bulbs I would be happy, I really dislike the brooder lights or the enormous wooden canopies with vertical bulbs...
It would be placed directly over the aquarium which has a glass top.