but theres one thing
when the mylar isnt perfectly flat I seemed to notice hot spots whereas a mirror wont do that. I know you are probably right though. and I have plenty of mylar so I'm not worried about ruining it. what happened actually is I sprayed some takedown spray for pests and some got on my mylar and dulled it so while wiping it off I created scratches on it. It shined it right up though and brought back some effectiveness. Heres another Idea for you what about if you used two mirrors for a reflector up by your light? the reflection of the light bulb might be as bright as the bulb itself therefore increasing the effectiveness almost 3x. I have seen on a science website where they increased effectiveness of solar cells by 3x by having mirrors reflect light from the sides and into the solar cell. being the mirror is flat I would think it wouldnt create any hot spots hotter than the bulb itself whereas the standard reflectors are bent and compress the light therefore creating hot spots.