Awsome! Ya that y splitters and double the amount of light = better yield! White walls/mylar is best. Not mandatory, but when growing with cfl lights, you only have a useable range of light to about 4". So if you surround your plant with reflective material and light seal your box, then you can use ALL of the lumens being produced. I have mine in a box made of thermo ply ( for draft stop behind tubs, im a house framer) but it has reflective material on one side. And the.inside of my box is covered in a mylar-type pad material and iys light tight. I have 110w of cfl light goin (all 2700k since seed) and my plant is doing AWSOME!!