Key points:
- Blue wavelengths near 450 nm have been shown to suppress melatonin production in humans and cause wakefulness.
- Researchers designed two new LEDs that emit different wavelengths of blue light—one for daytime use and one for evening use.
- Saliva samples showed that the new LEDs increased nighttime melatonin levels by 12.2% and reduced daytime melatonin by 21.9%.
Since the invention of iPhones and tablets, researchers have cautioned against using them in bed too often as the blue light they emit disrupts production of the natural sleep hormone melatonin. Now, researchers report in ACS Omega that they have designed more “human-centric” LEDs that could potentially enhance drowsiness or alertness on command.
Blue light ranges in wavelength from 380 to 500 nanometers (nm), but not all blue light is created equal. The wavelengths that suppress melatonin production and cause wakefulness are in the range of 460 to 500 nm. So, the researchers designed two LEDs that emit different wavelengths of blue light. One LED, intended for daytime use, restricted its blue emissions to wavelengths close to 475 nm. The other LED, for evening use, emitted blue wavelengths near 450 nm.
The new LED bulbs were then placed along with conventional LED bulbs in fixtures installed in the ceiling of a windowless room furnished with a desk, treadmill and bed. Twenty-two male volunteers stayed in the room for a stretch of three days. A computer controlled which type of LED was turned on or off during the stay; that way, the researchers could compare the impact on melatonin levels of conventional bulbs versus the new daytime and evening bulbs.
Saliva samples from all 22 volunteers showed that using the new LEDs increased the participants’ nighttime melatonin levels by 12.2% and reduced daytime melatonin by 21.9% compared with consistent conventional LED exposure.
The researchers say they hope manufacturers of LED lamps and electronic displays can apply these findings to help people increase daytime vitality and work efficiency while also improving nighttime relaxation and sleep quality.