1. A flame detection apparatus for detecting fires, comprising: first and second infrared detectors, said first detector sensitive to a wavelength emitted by combustion of hydrocarbons and other carbon containing materials, said second detector sensitive to infrared wavelengths present in sunlight and emitted by artificial radiation sources; a data acquisition system coupled to outputs of said first and second infrared detectors, said system adapted to analyze and interpret the signals generated by the two infrared detectors to detect radiation from a fire while distinguishing sunlight and artificial radiation sources, said system including a first channel coupled to a first detector output of said first detector for analyzing the flicker rate of low frequency components of said first detector output to detect amplitude fluctuations characteristic of small fires, and a second channel coupled to said first detector output for analyzing the flicker rate of high frequency components of said first detector output to detect amplitude fluctuations characteristic of large fires.