Researchers have designed and tested a "human-centered" LED that emits different wavelengths of blue light depending on day or night, thereby reducing the interference of artificial light on our biological clocks. They hope manufacturers can apply their research results to produce this new type of LED.
Because our body clock, the circadian rhythm, is synchronized with nature's light-dark cycle, we must use or be appropriately exposed to light. However, in modern society, many of us are exposed to large amounts of indoor artificial light, which can throw our circadian rhythms out of whack and lead to sleep disorders.
More than any other color of light, blue light disrupts the body's ability to prepare for sleep because it tricks our brains into thinking it's daytime and inhibits the secretion of our "relaxation" hormone, melatonin. The intrinsically photosensitive retinal ganglion cells (ipRGCs) in the retina of the eye are particularly sensitive to the absorption of blue light with a wavelength of 480 nanometers, and previous research has shown that blue light with a wavelength of 460 nanometers to 500 nanometers regulates our circadian rhythms.
To address blue light's interference with human rhythms, researchers have developed a so-called "human-centric" LED designed to deliver the right type of blue light at the right time of day.
Realizing that two different wavelengths of light affect circadian rhythms, the researchers created two LEDs: one that emits light at a wavelength of 480 nanometers "during the day" and one that emits light at a wavelength of 450 nanometers "at night." These two LEDs are then put into a light bulb. Phosphors are encapsulated in the bulb to convert some of the blue light into red and green light like a traditional light bulb.
Human-CentricLED (HC-LED) bulbs were installed along with conventional LED (c-LED) bulbs on the ceiling of a windowless room containing a desk, treadmill, and bed. The study recruited 22 healthy adult male volunteers who were randomly assigned to HC-LED or c-LED lighting (480 nm). All participants were exposed to both types of lighting as well as daylight/nighttime lighting and remained in the room for three days. Participants may use electronic devices such as smartphones and computers, but must use blue light filters.
Melatonin levels were measured by collecting saliva samples at 15 time points (and lighting conditions) over a 50-hour period, including between midnight and 3:00 AM. The researchers found that exposure to HC-LEDs increased participants' nighttime melatonin levels by 12.2% and decreased daytime melatonin levels by 21.9% compared with exposure to c-LEDs.
The researchers hope that manufacturers of LED lamps and electronic displays can apply their findings to produce HC-LED lamps. Most monitors, including smartphones, televisions, and computer monitors, support modes that block blue light at night (BLAN), but no mode quickly suppresses melatonin by boosting blue light during the day.
"HC-LEDs are expected to improve the circadian rhythm by controlling the light wavelength band directly related to melatonin, and will become a useful item for maintaining a healthy circadian rhythm in modern life," the researchers said.
The research was published in the journal ACSOmega.