Neutral daylight illumination with electrochromic glazing: simulation of ‘light mixing’

Electrochromic glazing generally exhibits a shift in spectral transmission as the glass darkens, e.g. causing it to appear blue as it tints. Occupants however are believed to prefer a neutral spectrum of daylight illumination without any pronounced hue. In this paper the authors show that it is possible to maintain a neutral spectrum of illumination with EC glazing under normal operation provided that just a small proportion of the EC glazing is kept in the clear state. Predictions from a theoretical model are compared with measurements of the daylight spectra in an office with EC glazing under various states of tint. The predicted spectra show excellent agreement with the measurements. The theoretical model is further validated using lighting simulation to demonstrate that, under normal operation, illumination from clear and full-tint EC is well-mixed, with that from clear glazing dominating the overall illumination.