A repeated measures design was used, with two independent variables: screen luminance (or light intensity emitted from the screen) and light wavelength. The first, luminance at two levels: low - 80 lux (35mw/cm2) and high - 350 lux (160mw/cm2). The second, wavelength at two levels: short (SWL)-485 nm (13500k) and long (LWL)-620 nm (4250k). Luminance and wavelength levels were measured and adjusted using a light metering device (AvaSpec-2048-FT-SDU; Avantes, Inc., Eerbeek, Netherlands). There were three dependent measures that were analyzed separately, sleep, melatonin secretion, and oral temperature. Each participant underwent all four experimental conditions in counterbalanced order.