Figure 1.

(a) Fluorescence quantum yield Q_av of many types of visible fluorescent proteins (VFPs) versus their peak emission wavelengths obtained from the literature.²¹ The quantum yield was determined using ensemble-averaging methods that do not discriminate between dark and bright states. (b) (left) Cartoon of an ensemble of identical emitters that yield an accurate value for the fluorescence quantum yield when using a method that averages over the whole ensemble. (right) Cartoon of a heterogeneous ensemble of bright and dark emitters. The presence of dark emitters limits the apparent quantum yield determined by averaging methods.