simulated solar light (290–1200 nm) or to blue light (380–480 nm)
(Fig. 6). Exposure for two 30 min periods resulted in the
appearance of vitamin D in skin with both light sources (Fig. 7),
with full spectrum simulated sunlight producing more vitamin D
than blue light. Furthermore, increasing amounts of 1,25(OH)2D3
were detected in blood of these
fish after irradiation (Fig. 8). The
identity of vitamin D obtained from the skin of trout irradiated
with 380–480 nm blue light was confirmed by mass spectrometry
(Fig. 9). In other experiments in which dead rats, with the hair coat
closely clipped to the skin, and dead trout were both exposed to
380–480 nm blue light, vitamin D was again found in the trout skin
but there was no change in the small quantities of vitamin D in rat
skin. It was, therefore, concluded that some characteristic of trout
skin structure had enabled the energy of blue light to convert
7-dehydrocholesterol into cholecalciferol.