Light-emitting diodes and cool white fluorescent light similarly suppress pineal gland melatonin and maintain retinal function and morphology in the rat.

Background and purpose: A novel light-emitting diode (LED) light source for use in animal-habitat lighting was evaluated.

Methods: The LED was evaluated by comparing its effectiveness with that of cool white fluorescent light (CWF) in suppressing pineal gland melatonin content and maintaining normal retinal physiology, as evaluated by use of electroretinography (ERG), and morphology.

Results: Pineal melatonin concentration was equally suppressed by LED and CWF light at five light illuminances (100, 40, 10, 1, and 0.1 lux). There were no significant differences in melatonin suppression between LED and CWF light, compared with values for unexposed controls. There were no differences in ERG a-wave implicit times and amplitudes or b-wave implicit times and amplitudes between 100-lux LED-exposed rats and 100-lux CWF-exposed rats. Results of retinal histologic examination indicated no differences in retinal thickness, rod outer segment length, and number of rod nuclei between rats exposed to 100-lux LED and 100-lux CWF for 14 days. Furthermore, in all eyes, the retinal pigmented epithelium was intact and not vacuolated, whereas rod outer segments were of normal thickness.

Conclusion: LED light does not cause retinal damage and can suppress pineal melatonin content at intensities similar to CWF light intensities.