Stimuli are perceived as lasting longer when there is something bright on the screen.

Perceived time often diverges from physical time. This discrepancy is important given the crucial role of time perception in numerous cognitive processes. A critical question concerning the non-veridicality of timing is whether and how different physical attributes (e.g., size, speed, and numerosity) influence perceived duration. The present study deals specifically with how perceived time depends on stimulus brightness, both of a to-be-timed stimulus and the background on which this stimulus is presented. The results of two experiments show that increased brightness lengthens perceived duration, and, surprisingly, that this is the case both for the stimulus and the background. The finding that stimulus brightness affects time perception is a much needed replication of classic studies; however, the finding that background brightness similarly affects time perception is novel, and suggests that time perception may be biased by low-level visual perception. Additionally, we tested the hypothesis that large pupils (as a result of spontaneous pupil-size fluctuations) are associated with longer perceived durations. This hypothesis was based on the common assumption that arousal affects both pupil size and time perception; however, in contrast to this hypothesis, results show that pupil size has no relation to perceived time. Taken together, our study suggests that time perception is strongly affected by low-level visual input (brightness) but not-or hardly-by pupil-linked arousal.