A film formation system 10 has a processing chamber 15 bounded by sidewalls 18 and a top cover 11. In one embodiment, the top cover 11 has a reflective surface 13 for reflecting radiant energy back onto a substrate 19, pyrometers 405 for measuring the temperature of the substrate 19 across a number of zones, and at least one emissometer 410 for measuring the actual emissivity of the substrate 19. In another embodiment, a radiant heating system 313 is disposed under the substrate support 16. The temperature of the substrate 19 is obtained from pyrometric data from the pyrometers 405, and the emissometer 410.