Hue-heat hypothesis: A Step forward for a Holistic Approach to IEQ

For many years different human factors contributing to the IEQ have been studied separately. Concerning thermal perception, despite it is almost accepted that thermal comfort can be influenced by concomitant stimulation of non-tactile modalities, relatively few investigations have succeeded in delineating non-tactile stimulations as the visual ones. The hue-heat hypothesis is based on the idea that, when spectral irradiance pattern at the observer's eye shows a great amount of short wavelengths, the space is perceived as cooler. Conversely, when long wavelengths are predominant, the space is perceived as warmer. This means that operating on light characteristics could help in improving thermal comfort for the occupants with possible energy savings obtained by acting on the set-point temperature of HVAC systems. To verify this hypothesis, this paper will deal with a subjective investigation carried out in a special mechanically conditioned test room equipped with white-tuning LED sources. Investigated subjects have been exposed to two different light scenes consisting of warm (3000 K) and cool light sources (6000 K) at a fixed task illuminance value. Preliminary results seem to demonstrate that cool light is effective in shifting to cool the perceived thermal sensation with a general increase of people under neutral conditions.