Circadian Lighting

Scientists identify exact light to trigger sleep-wake cycle

A close-up of an eye with blue light
A paper, published in the Journal of Biological Rhythms today, reveals that 477 nanometres is the most potent light to control people’s circadian rhythm.

SCIENTISTS say they have identified the exact wavelength of light which controls the sleep-wake cycle of humans. 

A paper, published in the Journal of Biological Rhythms today, reveals that 477 nanometres is the most potent light to control people’s circadian rhythm. 

The researchers have dubbed it ‘Circadian Blue’.

The study has major implications for how artificial lighting will be engineered to optimise human health.

Blue light exposure at night is a well-established public health hazard. It suppresses melatonin, the body’s sleep-wake hormone, and causes circadian disruption, and is linked to an increased risk of sleep disorders, obesity, diabetes, and breast and prostate cancer. 

‘Our goal was to define the exact wavelengths of light that trigger the human circadian system in real-world lighting conditions’ said Dr. Martin Moore-Ede, a former professor at Harvard Medical School and CEO at Circadian ZircLight. 

‘We found the critical blue light signal falls between 438-493nm with a peak at 477nm. This is the missing key to managing the health risks of light at night.’ 

The Circadian Light Research Center team used an interesting feature of white light to tease out the circadian-sensitive wavelengths: white lights can be built from a wide variety of colour spectral combinations.

They recruited 34 male and female study subjects, who were exposed on each test night to a different LED or fluorescent white light spectra for 12 hours. Throughout each night, melatonin levels were measured. 

‘We found melatonin suppression levels varied widely depending on the light source’s unique spectral characteristics,’ said Dr. Anneke Heitman, a study co-author. 

‘This data enabled us to isolate the impact of individual wavelengths of light and determine the colour of Circadian Blue.

‘Previous research into the spectral sensitivity of the circadian clock was done in dark-adapted conditions with short exposures to monochromatic lights. 

‘However, at home and at work, we spend the vast majority of our time in a light-adapted state, exposed to white polychromatic light,’ said Dr. Moore-Ede.

‘Our study reflects how we interact with light in the real-world.’

Based on these findings, the company Circadian ZircLight has built and patented spectrally-engineered LEDs that synchronise circadian rhythms during the day and prevent circadian disruption at night by controlling the Circadian Blue dosage. 

The firm said this work led to the first UL verified LED to emit less than 2 per cent blue light at night. 

In addition to building their own fixtures, Circadian ZircLight has licensed the LED technology to other lighting companies, including Acuity Brands, to meet the growing demand for circadian lighting. 

Circadian ZircLight says it expects to have lamps for the domestic market next year.