Quantum Efficiency

Quantum efficiency (QE) is a quantity defined for a photosensitive device such as photographic film or a charge-coupled device (CCD) as the percentage of photons hitting the photoreactive surface that will produce an electron–hole pair. It is an accurate measurement of the device's sensitivity. It is often measured over a range of different wavelengths to characterize a device's efficiency at each energy. Photographic film typically has a QE of much less than 10%, while CCDs can have a QE of well over 90 t some wavelengths.
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In an optical source or detector, the ratio of the number of output quanta to the number of input quanta. Note: Input and output quanta need not both be photons.