Temperature measurement using a pyrometer in a processing chamber is described. The extraneous light received by the pyrometer is reduced. In one example, a photodetector is used to measure the intensity of light within the processing chamber at a defined wavelength. A temperature circuit is used to convert the measured light intensity to a temperature signal, and a doped optical window between a heat source and a workpiece inside processing chamber is used to absorb light at the defined wavelength directed at the workpiece from the heat source.