Chlorophyll fluorescence appears to be a measure of photosynthesis, but this is an over-simplification. Fluorescence can measure the efficiency of PSII photochemistry, which can be used to estimate the rate of linear electron transport by multiplying by the light intensity. However, researchers generally mean carbon fixation when they refer to photosynthesis. Electron transport and CO fixation can correlate well, but may not correlate in the field due to processes such as photorespiration, nitrogen metabolism and the Mehler reaction.