The way chlorophyll works, usable light passes through one-way. Lighting from the underside is wasteful, you're better off putting the light inside the canopy, not underneath it.

If you had a centrifuge and could make a suspension of chlorophyll in a test tube, then had an incandescent light to observe the tube, you'll see two different things depending on the orientation of tube and light relative to you. If you held the tube in front of you and had a light next to you, you would see the tube as green. Now, take that light, put the tube between the light and your field of vison, suddenly you're seeing red. This is a characteristic of aggregate chlorophyll. Now the little bit of reflecting light from the undersides of the leaves hitting the tops of other leaves helps, yes, but otherwise quite a bit of light is being wasted.

I've tested this many times in my younger days. Underside lighting is rather wasteful, side or inside lighting is much better.
khyberkitsune Reviewed by khyberkitsune on . Lighting Grow From Underneath? i went by a buddies place this morning to check out his grow for him and see how things were going. hes growing in a space about the same size as mine. hes got 8 plants (4ft tall) on flower right now with 1 1000w MH above them (he never uses HPS and always grows nice tight crystallized potent firebud) , but he has a 500w output florescent on the ground shining up into his plants. in the middle of his grow. ive been growing for years and never saw such a thing (side lighting?...yea, Rating: 5