You don't need much to grow chaeto at all. A 6500k CFL or LED bulb on a standard light fixture is plenty. I grow mine with a small JBJ LED refugium light and it grows no problem with that and it's connected to the side wall of my sump w/ the light having to penetrate through the glass.
i use one of them 39 dollar marineland led on my sump and have it switched to just blue 24/7 and i switch to all leds when i cleaning skimmer and working in sump