Context-robust influences of illumination on perceived friendliness of faces

Interpreting people’s facial expressions at dim lighting conditions can be challenging and the perception of facial expressions might be influenced by lighting qualities. This is important to lighting designers trying to accommodate for friendly urban environments at dark, especially for public places with a high degree of social activity and social interaction. In an earlier rating experiment, judgments of the “friendliness” of photographed Styrofoam heads under different lighting directions were shown to vary. In the current experiment we tested whether such judgments depend on context. A set existing of a rendered face under ten systematically varied illuminations was superposed on five different backgrounds: White neutral, Grey neutral, Friendly forest, Creepy forest, and Neutral forest. The mean luminance for the grey neutral and three forest scenes was equalized. 20 subjects rated the ten differently lighted heads on the five different scenes on a 7-step friendliness scale, from very unfriendly to very friendly. Results showed that perceived friendliness varied consistently in similar manners as was found earlier and showed no significant consistent differences between the five scenes. For a neutral facial expression, we found that the perceived friendliness varied from light from below right giving most unfriendly (means around 2.5) and light from above giving most friendly (means around 4.5) ratings. This suggests that lighting qualities are a major factor in perception of facial expressions, and that the main effects might be quite robust throughout different contexts. When considering light installations this should be taken in account. In future studies we will randomize the images of the heads and background, and render the complete scene i.e., head and context.