[en] A study of the use of phototherapy was conducted in nine Norwegian hospitals. It was particularly focused on the light sources and the irradiation methods. Large differences were found between different hospitals and between single units within the same hospital. Irradiance values varied with a factor of more than ten and a number of different light sources were in use. It is recommended that a certain standardization of the treatment is performed in order to improve the therapeutic efficiency and to limit the risk of unwanted side effects. 15 refs., 16 figs