Focused radiation, the second law of thermodynamics and temperature measurements

The paradox proposed by Panse (1992)-that some reflector systems can focus sufficient radiation from a number of objects to heat another to a higher temperature-has been resolved for two specific cases. The problem highlights the fact that all focusing systems must be limited by the second law of thermodynamics, whence a corollary to the second law is proposed for focusing systems. The states that 'no system may focus from one object, through an aperture onto a second identical object, more radiation than may be emitted by the second object through the same aperture'. The application of this type of system to non-contact temperature measurement is discussed.