"But I'm not sure how much affect it will really have. I just figure it's more light shooting back at the plant....so it can't be a bad thing! "

Well, I'll tel you it doesn't work very well. If you take a test tube of chlorophyll and an incandescent light, depending upon the location of the tube relative to you and the light, it will either appear green, or red. With the test tube in front of you, between you and the light, you will see red, with the test tube in front of you, and the incandescent bulb beside or behind you, you will see it as green. Chlorophyll has some properties of a metamaterial, and as such light doesn't act in the typical fashion when it strikes those tissues.

Lighting from the underside is not that viable of an idea. The mesophyll layer is also closer to being on the top of the leaf (typically right under the eipdermis and spongy layer,) and the underside tends to block light, making underside lighting far more inefficient.