The invention relates to a system for controlling work lights in a forestry machine, which system includes a harvester head (16), attached to the set of booms (14) of the forestry machine (10), for felling and processing trees, at least one work light (20) attached to the harvester head (16) for illuminating the harvester head (16) and its surroundings, and control means (15) for controlling the operation of the work light (20). The control means (15) are the valve control unit (25) belonging to the harvester head (16) for controlling the valves of the harvester head (16), which control unit (25) is arranged to feed power and/or control the power feed to the said work light (20).
