Abstract
Visual experiments in psychology, psychophysics, and cognitive neuroscience require precise control over stimulus characteristics, such as luminance and contrast. In such experiments, stimuli are most often presented using computer monitors. These monitors bear an often neglected and rarely reported source of experimental confounds and uncontrolled variation: they take a warm-up time in which their luminance systematically changes until a stable level is eventually reached. Here we demonstrate this problem by measuring luminance over time for five different monitors. Results indicate that not only the warm-up time but also the course that the warm-up takes can vary greatly between different monitors. To address this problem, we propose a simple method of approximating a monitor\IeC {\textquoteright }s warm-up time, which takes into account theoretical considerations of the specific experiment. On this basis, we suggest a standardized experimental procedure and a standardized way of reporting its results to enable experimenters to control for monitor warm-up time.