Quantification of visible light-induced melanogenesis in human skin.

Exposure of normal skin to visible light (400-700 nm) resulted in the induction of immediate pigment darkening (IPD), immediate erythema and a persistent (delayed) tanning reaction. The intensity of pigmentation and time course of the reaction were monitored by measuring chromaticity coordinates. Both IPD and immediate erythema faded over a 24-h period but, unlike erythema, the pigmentation did not totally disappear and the residual tanning response remained unchanged for the rest of the 10-day observation period. The threshold dose for IPD with visible light was between 40 and 80 J/cm2, while the threshold dose for "persistent" pigmentation was greater than or equal to 80 J/cm2.