It may seem to be a stupid question but please take a serious look at it: 1) (hypothetical): Imagine a perfect hollow orb (ball, sphere...) of some heatproof material - inside metallized to reflect most wavelenghts of light (a one-way-mirror). Assumed a perfect vaccum inside: what happens if you put this ball into sunlight? 2) (practical): Constructing an octahedron (or even more sides) of one-way-mirrors and optimizing the design could lead to objects even more efficient in transmuting sun energy than solar cells, couldn't it? I think thermal balance of such an object would be reached at relative high temperatures. Do I miss something in my considerations or am I completely naive thinking? 3) (simplified): Consider a setup of 2 parallel mirrors - one of them being one-way: projecting a laser beam through the one-way-mirror: what happens if the laser is projecting continously?