Thermal qualification of space equipment is performed in a thermal/vacuum (T/V) chamber. Here the chamber pressure is maintained near 10−6torr, imitating the vacuum of space and ensuring that all heat transfer occurs by conduction and radiation. In addition, the chamber walls are flooded with liquid nitrogen to simulate the background radiation from space.When performing tests in T/V conditions, an equivalent sink temperature for the test article is normally specified. However, the quartz infrared lamps that are currently used in T/V testing cannot be used to provide a uniform sink temperature over surfaces with varying optical properties. The present work defines an innovative method of applying the sink temperature that yields uniform results despite variations in the surface optical properties.