A handheld device has a light source (30, figure 3), a movement detector (34) which measures the speed of movement of the device over a user s skin, and a control means (36) for modulating the amount of radiation emitted by the light source in accordance with the detected speed such that a constant radiation density is applied to the skin. Preferably, the modulation is achieved by varying the duty cycle of the light source, but its intensity may be adjusted instead. The motion sensor may be a roller or an image detector. When the device is stationary the control means reduces the amount of radiation to nil, or to a low value. Also disclosed is a device which detects the reflectance of the skin and alters its output accordingly, and a device which can crop hairs and then destroy the hair follicles by changing the direction of its light beam output.
