So. You have yourself a mirror, and you have yourself a ridiculous bright source of light. Maybe it’s a laser and an aiming mirror, maybe it’s the sun and a solar sail deployed at a dangerously close perihelion. Since no mirror is 100% reflective, some of the light is absorbed and the mirror temperature climbs. Assume the mirror is made out of something that can take very high temperatures (say, iridium)… so high that the mirror becomes incandescently hot without melting. So, the question is… if your shiny iridium mirror is glowing white hot… is it still a reflector? I know that with gases, the most transparent vapor become a near-perfect absorber of incoming radiation if it’s incandescent. But how about a solid reflector?