Effects of short wavelength control in polychromatic light sources on nocturnal melatonin secretion

In this study, 12 healthy males were exposed to various light conditions (2300 K, 3000 K, 5000 K and dim) for 1.5 h at midnight. The conditions of 3000 K and 5000 K were created by commercial fluorescent lamps. The light at 2300 K was achieved by fitting a 3000 K fluorescent lamp with a special filter that absorbed short-wavelength light. The vertical illuminance level was kept at 200 lx. Saliva samples were taken before and after the light exposure. The light at 5000 K suppressed melatonin secretion acutely. The 2300 K lamp condition appeared to have no effect on melatonin secretion as well as the dim condition, while melatonin secretion was measurably suppressed by the light at 3000 K. (c) 2008 Elsevier Ireland Ltd. All rights reserved.