Figure 1. The skin of a two-year-old boy with mental retardation appears unspotted in a photograph taken in normal daylight (left-hand panel). A photograph taken under Wood's light shows a hypopigmented spot in the shape of a leaf from the mountain ash tree (right-hand panel). Wood's light is a blue light with an emission peak of 360 nm. The blue end of visible light is absorbed by epidermal pigmentation. If there is no epidermal pigmentation in a site, the area will appear nonpigmented as compared with the surrounding skin. Minimally visible hypopigmented spots are more easily visualized with the Wood's . . .