Clamp lamps will work just fine on a 55. I think 4 would be ideal, since a 55 is 48" long and you can get 10" clamp lamps. I would *strongly* suggest you start with 13w CFLs rather than 23w because your aquarium will be new and you will struggle with the various algaes that pop up. 13w will be more than ample for your needs. I can't emphasize this enough. The #1 mistake people make is over-driving with light.