A light source is provided capable of maintaining the temperature of a collector surface at or below a predetermined temperature. The light source in accordance with various embodiments of the present disclosure includes a processor, a droplet generator for generating a droplet to create extreme ultraviolet light, a collector for reflecting the extreme ultraviolet light into an intermediate focus point, a light generator for generating pre-pulse light and main pulse light, and a thermal image capture device for capturing a thermal image from a reflective surface of the collector.