What kind of lightbulb for 20 gal aquarium?

Well I have 3 fish tanks, a 10 gallon hospital, 20 gallon community, and 50 gallon community. my 50 gallon has a tube lighting sort of thing, and the bulbs I get make the lighting look more natural, but my 20 gallon has the yellow lights which I hate... Im currently using the Marina aquarium light bulb, 15w 120v, Long lasting. My tank takes 2... what kind of light bulb should I use to get the non-yellow lighting. because I can't find any bulbs that do what the tube one does. any ideas?