Although using daylight is a strategy for reducing lighting energy, its effect on space brightness perception remains unclear. A few studies that examined the effects of daylight demonstrated that the brightness produced by daylight was not as efficiently enhanced as expected by horizontal illuminance. However, they did not consider the scenic views through windows. In this study, as a pilot study toward generalizing brightness estimation indices in the future, we investigated the effects of daylight on space brightness with different scenic views (natural and urban) outside a window, with different window types (regular and frosted glass windows), and with or without a human form (a human-shaped board covered with a full-length photograph of an adult male placed in front of the window). In our experiment, we used two scale models to simulate two offices: a room with a window (test room) and a room without a window (reference room). In each trial, the observers viewed the two models and rated the space brightness of the test room relative to that of the reference room. The results showed that the estimated brightness values “at the same illuminance” and the efficiency of brightness enhancement provided by daylight was lower in the case with a scenic view than that without a window, and the pattern of the results did not change with a human-shaped board. This general tendency aligns with the findings of a previous study, but neither qualitative nor statistically significant differences were observed between the landscape or window conditions (scenic views and frosted glass). In a previous study, there is a developed provisional model for space brightness using the brightness equation. We examined whether this equation is applicable under the conditions of the present study.
Yamada et al. (2026) studied this question.