Don't use a light meter, use a laser thermometer and do a side by side comparison. I would, but I don't have a laser thermometer.
Opie Yutts Reviewed by Opie Yutts on . Mylar vs. foil For a long time I assumed everyone knew what they were talking about when they said not to use aluminum foil, and to use mylar. Apparently foil can create hot spots. But here's the thing, so can mylar. In fact, it's often used precisely because of its ability to reflect heat! Anyway, I've heard all sorts of misinformation, like that aluminum foil is only 40% reflective whereas mylar is 98% reflective. So I looked up some data in my thermodynamics textbook from college. Actually, Rating: 5