has this been done? i just had this crazy idea of cutting a wedge to accommodate the main stem and placing unwanted CDs/DVDs face down on the soil. i know a guy who knows a guy who has a lot of them, and they would be more durable than tinfoil at least.
suppose the grower superglued little lego spacers or "feet" to the bottom (in fact the labeled top/front side) of the upside-down disc, to keep it elevated above the soil surface. once the airflow concern is addressed, would this be worth doing? i'm afraid i don't understand the physics of bouncing light well enough to guess.
Other then what the above said you would probably eventually have a nice mold build up since the evaporated water would hit it.
Use them or not probably wont have a major impact. The light reflected back is only about 10% of the total light given. Wont make or break you.