Hamamatsu UVTron Flame Detector

The UV-Tron is a unique sensor for detecting flames. It is extremely accurate and can detect a lit candle from several meters away. The sensor uses a Photomultiplier Tube, or PMT, to detect photons in the ultraviolet wavelength that match the signature of a flame. It works in broad daylight flawlessly. In fact, you'll probably need to put a baffle around it in order to use it properly.