Embodiments of the present invention pertain to substrate processing equipment and methods incorporating light emitting diodes (LEDs) for thermally processing substrates. Such light sources offer a variety of advantages including higher efficiency and more rapid response times. Pulse widths are selectable down to under a millisecond but can be for long pulses up to and exceeding a second. LEDs are preferable to tungsten-halogen lamps even in circumstances that allow longer processing times, since LEDs produce light with greater than 50% efficiency and tungsten-halogen lamps operate with less than 5% efficiency.