People spend much of their time in buildings. This means the indoor environment (temperature, light, air and noise) affects our health, comfort and productivity during the day. Buildings use a lot of energy to regulate temperatures in buildings, but this does not always lead to healthy conditions and satisfied building users. This dissertation looked at how light conditions affect the temperature perception, alertness and thermophysiological parameters such as body temperature. An important conclusion is that light conditions that are experienced as comfortable also have a positive effect on the temperature perception. Energy-efficient led lights can potentially be used to apply large temperature variation in buildings and thereby reduce en...