The effect of thermochromic windows on visual performance and sustained attention

Thermochromic windows have been widely studied as a technology that can potentially offer increases in energy conservation and provide a desirable luminous environment inside buildings. However, there has been little attention placed on how the tinted states of thermochromic glazing influence occupant behaviour and visual perception. An experiment under controlled conditions was designed to test the influence of different thermochromic tint states on human response. By using a controllable artificial window, five typical luminous conditions were set up, including clear (no tint) and two different levels of blue and bronze tint states, which produced different room colour temperatures. Thirty-one subjects were recruited who completed three visual tasks, including the visual acuity and colour naming tasks using the coloured Landolt ring chart and a sustained attention test using the d2 test. Subjective assessments were also collected using questionnaires. Statistical analyses showed that across the thermochromic window conditions, no significant differences in performance were found for the visual acuity and d2 tests. However, there was a significant effect for the colour naming task from the Landolt ring test. Under blue tint conditions, subjects reported higher alertness and produced fewer errors. More natural and acceptable lighting conditions were found under the bronze-tinted conditions. Therefore, when developing innovative thermochromic windows applied in buildings, it is important to cater for the visual requirements of the occupants in the space, not only energy efficiency goals.