Why good guys wear white.

Affect is a somewhat abstract concept that is frequently linked to physical metaphor. For example, good is often depicted as light (rather than dark), up (rather than down), and moving forward (rather than backward). The purpose of our studies was to examine whether the association between stimulus brightness and affect is optional or obligatory. In a series of three studies, participants categorized words as negative or positive. The valence of the words and the brightness of the letters were varied orthogonally. In Studies 1, 2, and 3, we found that categorization was inhibited when there was a mismatch between stimulus brightness (e.g., light) and word valence (e.g., negative). Studies 4 and 5 reveal boundary conditions for the effect. The studies suggest that, when making evaluations, people automatically assume that bright objects are good, whereas dark objects are bad.