yield is a term used in fluorescence
spectroscopy to define the effiency with which a compound takes light
that it absorbs
and converts it to emitted light. If a compound absorbs light and emits nothing (i.e. dark), then the quantum yield is zero. If every photon
absorbed results in photon emitted, the quantum yield is one. Tryptophan
, for example, has a quantum yield of 0.14, the highest of all the amino acids
Compounds with a high quantum yield are often useful to spectroscopists because it is much easier to detect their fluorescence.