Various spectral regions isolated from mercury and carbon arcs affect wool as follows: ultraviolet at 331 mµ and below increases yellowness, visible light above 398 mµ decreases yellowness, and the transition region in between does both. Thus, near uv, at 365 or 389 mµ, yellows wool in the first few minutes but subsequently removes this yellowness and then continues to bleach the wool. Aside from the visible effects, the various uv bands, even when close together, have distinct effects upon the uv reflectance curves. The results with electric sources confirm, extend, and resolve those with sunlight.