I am not sure what they are exactly called. Those cones that vets put on dogs so they can't bite themselves. What if there was something like that covered in Mylar and then put around the base of the plant to help reflect the light upwards back onto the plant? Can plants only produce energy from the light being absorbed on the top of the plant or could they absorb light from the bottom of the plant?
They're called "Elizabethan collars" or E collars for short. Some people put foil on top of the soil to reflect light. Light bounces around until it gets absorbed by something, so it could potentially bounce off the foil or mylar, then hit another surface from which it could be reflected to the top side of a leaf. Personally, I need to look at or feel the soil to judge if it's dry, so I don't put anything on it. I don't think the collar would be worth the effort but it probably wouldn't hurt anything.