Current USA vs. Coralife...

[Ruth]

To further what Chin said I would also consider going with a bigger tank to start off.
There is a lot more that good light required to keep healthy coral IMO. Water quality is your first and foremost requirement for keeping healthy fish and corals. I would rate water quality and water movement ahead of light when it comes to the health of a reef system.
With a 20g tank it is a lot harder to keep pristine, consistent water quality than it is with a larger system - it can be done with a low bio load, good skimming, good water movement, meticulous water changes and cleaning.
JMO