Improvized small aquarium lighting
Plenty of cool white (and straight UV, if you like) LEDs are available (and the cool types actually have better lumens-per-watt efficiency than the "warm" types, as a general rule.) 

Lumens-per-watt efficiency is all over the map, so you have to check the particular LEDs you are considering using. Some are awful, some are quite good.

Cooling is something you'll have to sort out, especially with high power LEDs, where thermal design is most of the design work. Stock aquarium hoods are terrible for it, so most folks with serious lighting setups end up building something that allows the lamps to cool more effectively (may involve a fan, may involve a barrier between the water and the lamp which will slightly reduce light into the aquarium, but greatly reduce humidity at the lamps, etc.)

One factor you may have missed is that the LEDs drive all the light towards the water, where the florescent has considerable losses from the parts of the lamp where light is reflected before hitting the water. I have 8.9 watt LED ceiling fixtures which are undeniably brighter than 13 watt CFLs for exactly this reason, even though they are "only" 70 lumens per watt.