For a 300 gallons refugium? or a refugium for your 300 gallons DT tank?
Depending on what you plan to keep in the refugium. A simple clip on 5600k light bulb will do or a grow light from ebay or amazon would be suffice to grow macro.
I've gotten great growth from the cheap black boxes running the white channels only. Once that died, I switched to a par 38 LED from Cree and it's ok for chaeto, so now that I upgraded to RB photon v2+ for my DT, I took one of my current ocean revives to use with my fuge and guess what? The white channels produces quick growth of chaeto.