  The delayed luminescence of biological tissues is an ultraweak reemission of
absorbed photons after exposure to external monochromatic or white light
illumination. Recently, Wang, B\'okkon, Dai and Antal (Brain Res. 2011)
presented the first experimental proof of the existence of spontaneous
ultraweak biophoton emission and visible light induced delayed ultraweak photon
emission from in vitro freshly isolated rat's whole eye, lens, vitreous humor
and retina. Here, we suggest that the photobiophysical source of negative
afterimage can also occur within the eye by delayed bioluminescent photons. In
other words, when we stare at a colored (or white) image for few seconds,
external photons can induce excited electronic states within different parts of
the eye that is followed by a delayed reemission of absorbed photons for
several seconds. Finally, these reemitted photons can be absorbed by
nonbleached photoreceptors that produce a negative afterimage. Although this
suggests the photobiophysical source of negative afterimages is related retinal
mechanisms, cortical neurons have also essential contribution in the
interpretation and modulation of negative afterimages.
