Abstract: Apparatus for therapeutic or cosmetic photo-treatment comprises a flash lamp and a lamp operating circuit. The lamp is cooled by water in contact with the lamp which acts as an infra-red filter to reduce skin burning. Light from the lamp reaches the skin through a light guide which has a convex curved end to focus the light and to press away haemoglobin in the target area or has a concave end to reduce pressure on the skin depending on the desired treatment. Relatively long and low power square shaped power pulses drive the lamp to produce light output pulses adapted to the relaxation time of the target structure to maximize the heating of the target while minimizing heating of the skin surface. Target structures may be blood vessels or hair follicles. Automatic detection of a glass filter may be provided.