623 Variations in in vivo visible light phototesting methodologies

While previously regarded as nonsignificant with minimal to no photobiologic effects, visible light (VL) has now been shown to have biologic effects on skin in subjects with all skin phototypes. However, currently there are no standardized guidelines to perform VL phototesting. A review of the published in vivo VL phototesting methodologies was performed to compare the various phototesting parameters. The methodologies were found to vary at multiple levels including spectral output of the irradiation sources, irradiance level, dosage, single vs. multiple exposures, assessment methods, assessment time points after irradiation, and calculation procedure for VL protection factor (VL-PF) among other variables. Variations in these parameters can cause significant differences in biologic response to VL. Burning and blister formation with VL irradiation reported in some studies, at doses that have been reported to be well tolerated in others, can be attributed to this. The growing interest in VL photobiology warrants careful investigation of the impact of above listed parameters. This in turn will aid in development of a standardized protocol enabling efficient comparisons among studies and establishment of adequate VL-PF