Lighting is a substantial energy consumer, and a major component of the service costs in manybuildings. Lighting renovation was done on the Department of Electrical and CommunicationsEngineering at the Helsinki University of Technology. The lighting in the renovated auditorium wasalmost 40 years old. New lamps with electronic ballast are more energy efficient and the ballast lossesare smaller. Also the optical properties of the new luminiares have been greatly improved. This papershow the results obtained in one auditorium. The old luminaires with T12 lamps with oldelectromagnetic ballasts were replaced with new luminaires with T5 lamps and dimmable electronicballasts. The luminaire output ratio in old luminaires was 0,39 and 0,74 in new ones.The illuminance was more than doubled after the renovation and at the same time the powerconsumption was reduced 30 %.