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 lamp. Ash-leaf spots are only one variety of hypopigmented macules present on the skin of patients who have tuberous sclerosis.