A flame detector includes an infrared detector and a first window covering the infrared detector. A second window is positioned in front of the first window. The flame detector is adapted to reject light having a wavelength below approximately 2 μm and to reject light having a wavelength above approximately 6 μm, allowing detection of flame from multiple sources. In variations, the windows in combination with the infrared detector may provide the rejection or a band pass filter provides the rejection. Still further variations utilize notch filters or a band reject filter to provide notches of light to the infrared detector corresponding to the wavelength of different flame sources to be detected.