I'm using this, it was a cheap led grow light off eBay (there are lots of options). It keeps my ball of cheato pearling (producing small oxygen bubbles) constantly which is a sign of strong photosynthesis. I'm the 2.5 weeks I've had it running the ball of cheato in my refuge has tripled in size and this is on a brand new tank with very little bioload.
The light is 10" x 10" which work perfect for my fuge
The cheato is probably doubled since this picture
Sent from my iPhone using Tapatalk