No but it helps. Your going to lose some light outwards but if your growing with CFLs probably does'nt matter much they do not give off a whole lot of grow spectrum far. If your using anything other then a CFL I would def add something reflective.
Flat white paint works great. Its cheap.
Is it really "smart" to have a box. Yes it keeps things contained and you have rails on the top to hang stuff and rails on the side to attach things. Makes it easy. It also focus's all of the light on the plant none is wasted. You can reflect back 10-15% of the light back to the plant with reflective surfaces
Do you need one no not at all just makes it all easier imo. If I was to use a basement dont have one then I would not but Id build a grow room down there.
Edited by rhapsodyrcks, 08 September 2012 - 08:48 PM.