Because LED lights emit a high quantity of blue lightwaves, which scientists have increasingly found to reduce human melatonin secretion and disrupt the circadian rhythm, these types of lights are not ideal for night-time reading. Though research has shown that LED and fluorescent lights provide measurable benefits during daytime, their blue tint at night may cause significant damage to natural sleep cycles and contribute to serious long-term health problems, according to the Harvard Health Letter.
Researchers have found that human melatonin production is most sensitive to exposure to blue-green colors with light wavelengths between 459 and 485 nanometers, as reported by David C. Holzman in his article "What’s in a Color? The Unique Human Health Effects of Blue Light," published in Environmental Health Perspectives. While LED lights are more energy efficient than traditional incandescent light bulbs, Harvard Health Letter notes that they also produce more melatonin-suppressing blue wavelengths.
Because of the human eye's sensitivity to their blue wavelengths, LED and fluorescent lights provide benefits during the day, including reduced sleepiness, increased heart rate and alertness, and improved working memory. However, this same sensitivity causes LED and other fluorescent lights to be particularly harmful at night. One study showed that an hour of exposure to blue-light-emitting bulbs delays deep sleep cycles by 30 minutes, according to the Harvard Health Letter. Preliminary studies have also associated lowered melatonin levels with hormonal changes and some types of cancer.
To reduce the potentially harmful effects of blue wavelengths, Harvard Health Letter recommends that individuals use only dim red lights at night, wear blue-blocking glasses and avoid electronic screens within about three hours of bedtime.