The present invention relates to a device for administering electromagnetic radiation to human tissue, in particular light to skin. The device comprises a treatment head with a recess (10) in which the light is emitted and in which the air pressure may be decreased by a pump (11). The device also comprises a pressure gauge (8) for measuring the pressure in the recess (10). Above a certain threshold value the device will not function, because this indicates an incorrect positioning of the device on the skin, which might cause harm to persons. By providing the pressure gauge (8), an operator may determine whether the positioning of the treatment head is correct. The device is advantageously automated in that the pressure gauge (8) is connected to control means (5) for controlling the source (3) of radiation.