460 nm Blue Light Heavily Supresses Melatonin (study summary)

Nighttime light exposure can prevent sleep.

One study found 460 nm to have a strong negative affect on circadian rhythm.

Researchers sought to find the range of effects of 460 nm light exposure on alertness, thermoregulation, and heart rate.

Night time 460 nm light exposure will suppress melatonin, increase body temperature, increase alertness, and increase heart rate.

Three groups received 2 lux  polychromatic white light for 1.5 hours, followed by 2 hours of darkness.

One group received 460 nm. The second received 550 nm. The third continued in darkness.

Three groups then received 2 lux of polychromatic white light for another 1.5 hours.

All subjects had 7.75 hours sleep.

Subjects receiving 460 nm blue light experienced greater alertness and reduced sleepiness.

Their heart rates were higher than control groups’ heart rates, sometimes significantly higher.

Blue light subjects’ body temperatures rose 1.5 degrees over controls.

Self-reported sleepiness was lower in the blue light group than in the control groups.

The blue light correlated with melatonin shifts inconsistent with good sleep. The 460 nm group melatonin was suppressed through the evening and night, but then rose above the controls the next morning. This is the opposite of a healthy melatonin pattern.

460 nm blue light is more damaging than 550 nm blue light.

460 nm exposure higher body temperature, suppressed melatonin, and raised heart rates, compared to the control group.