Examples described herein generally relate to apparatus and methods for rapid thermal processing (RTP) of a substrate. The present disclosure discloses pulsed radiation sources, used to measure a broad range of low to high temperatures in the RTP chamber. In one example, two or more lasers, one of which emits pulses of radiation at 1,030 nm and one of which emits pulses of radiation at 1,080 nm, which measures temperatures below about 200° C., are used. In another example, two or more LEDs, one of which emits pulses of radiation at 1,030 nm and one of which emits pulses of radiation at 1,080 nm, are used. In yet another example, a broadband radiation source is used to emit pulses of radiation at least at 1,030 nm and 1,080 nm. These radiation sources are useful for detection of a broad range of low to high temperatures in the RTP chamber.