There are actual a couple different nonphotochemical quenching mechanisms,
including transmembrane potentials, gradients in pH and conversion of
energy to heat through the xanthophyll cycle.
Some references:
Demming-Adams, B. 1990. Biochim. Biophys. Acta 1020: 1-24
Schreiber et al. 1986. Photosyn. Res. 10: 51-62
Weis and Berry. 1987. Biochim. Biophys. Acta 894: 198-208
