Abstract: The invention describes a method for adjusting supply powers for a first source of artificial light (5, 5?, 5?, 5??) in a first zone (W) of a room (1) and of a number of second sources of artificial light (9, 9?, 9?, 9??, 11, 11?, 11?, 11??) in a number of second zones (K1, K2) of the room (1). Thereby, the first zone (W) is closer to an external light source (3, 3?, 3?, 3??) than the second zones (K1, K2), and the supply powers for the first and second sources of artificial light (5, 5?, 5?, 5??, 9, 9?, 9?, 9??, 11, 11?, 11?, 11??) are reduced when a level of combined light level (PComb), comprising light (L1) from the first source of artificial light (5, 5?, 5?, 5??) and light (Le) from the external light source (3, 3?, 3?, 3??), increases.