New studies show cycles of blue and red light promote circadian entrainment

Researchers from the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute and the US General Services Administration (GSA) recently published the latest in a series of studies exploring how light impacts alertness during the day and sleep quality at night in daytime office workers.

The study field tested an LED luminaire developed by the LRC to promote circadian entrainment and alertness in the office environment. Nineteen participants from three US Department of State office buildings in Washington, DC, completed the three-week study. The luminaires, mounted near the participants’ computer monitors provided the following light cycles:

1. Morning saturated blue light, delivering a circadian stimulus (CS) of 0.4
2. Midday polychromatic white light, delivering a CS of 0.3
3. Afternoon saturated red light, delivering a CS close to zero

The CS metric has been described in detail by LRC director Mariana Figueiro during the Lighting for Health and Wellbeing conference in 2018; you can learn more in the post-conference report by chief editor Maury Wright. Objective and subjective measures of rest–activity, sleep, vitality, and alertness were used to evaluate the lighting interventions.

Results show that participants exhibited more consolidated rest–activity patterns, indicating better circadian entrainment, and woke up earlier during the intervention compared to baseline. The morning blue light appears to have advanced participants’ circadian phase, causing participants to wake up earlier in the morning. The afternoon red light elicited an acute alerting response close to the post-lunch dip (around 3 PM), reducing subjective sleepiness and increasing subjective vitality and energy.

These field results are the first to demonstrate that red light in combination with ambient white light provides an effective alerting stimulus, and support the inference that light exposures, when properly applied, can promote circadian entrainment and increase alertness.

The research paper, “Light, entrainment and alertness: A case study in offices” was published earlier this month in the journal Lighting Research & Technology. Authors include Figueiro, Mark Rea, Levent Sahin, and Charles Roohan from the LRC.

Past studies help to refine the present

Previous LRC studies measured light levels for 109 participants at five federal office buildings designed to maximize daylight availability indoors. Figueiro and her team found that even in open offices with many large windows, office workers were not receiving enough light to stimulate their circadian system during the day, due to factors such as season, cloud cover, desk orientation, and window shade position.

In response to these findings, the research team theorized that supplemental electric lighting could be used to ensure that office workers receive enough light during the day, and installed circadian-effective lighting for 68 participants at four additional sites.

The study results showed that office workers felt much less sleepy with the use of supplemental electric lighting and, as hypothesized, they also reported feeling significantly more vital, energetic, and alert compared to baseline.

“The present findings show that a tailored lighting intervention can help entrain building occupants and can increase alertness during working hours. The ‘non-visual layer of light’ solution utilized in the present study is practical and inexpensive to implement, while helping to reinforce the bridge between laboratory results and field applications,” said Figueiro.

“Underwriters Laboratories (UL) will soon be publishing a Design Guideline for lighting offices, factories, and educational facilities aimed at promoting better sleep for day-active, night-inactive occupants of buildings. This study adds even more evidence that bright light during the day promotes and consolidates sleep at night,” said Rea.

The circadian-entrainment LED luminaire concept might be implemented into an office setting such as this one via workstation partitions, along with considered use of tunable ambient lighting. (Photo credit: Enhanced image renderings courtesy of the Lighting Research Center.)

How does light impact sleep?

Light has to enter the eye to be effective for circadian entrainment. People in modern society usually spend more than 90% of their time indoors in buildings, yet lighting indoors is typically not bright enough to stimulate the circadian clock. Typical office lighting provides less than 100 lx at the eye, whereas being outside on a sunny day will provide anywhere from 1,000 to more than 10,000 lx at the eye.

We now know that most people are not getting enough light during the day. Unfortunately, too little light during the day is compounded by too much light at night. Many people use luminous electronic devices like smartphones and tablets in the evening or stay up late working on the computer. Light from these screens makes the brain think it’s time to wake up, just as you’re getting ready for bed.

Disruption of the 24-hour rhythm of light and dark affects every one of our biological systems from DNA repair in single cells to melatonin production by the pineal gland in the brain. Circadian disruption is most obviously linked with disruption of rest–activity patterns, which can cause sleepiness during the day and insomnia at night, but it is also linked with increased risk for diabetes, obesity, cardiovascular disease, and certain types of cancer.

Exposure to a robust 24-hour light–dark cycle promotes circadian entrainment, which has many health benefits such as increased alertness and feelings of vitality during the day, improved mood, and better sleep at night. Recent research has shown that healthy, regular sleep patterns may even have a protective effect against Alzheimer’s disease.

A poster summarizing the entrainment results can be downloaded from the LRC website.

Get to know our expert

REBEKAH MULLANEY is the manager of research communications at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (RPI). Working alongside the research center director, Mullaney is responsible for promoting LRC research and increasing public awareness of the many ways in which lighting can benefit society and the environment — from improving human health to enhancing food production to managing clean energy in the new electric grid. Mullaney has worked in public relations, marketing, and editorial roles for Rensselaer Polytechnic Institute, the Naval Nuclear Laboratory, and Albany Molecular Research Inc. (AMRI). She has a BA from Kalamazoo College and an MS from RPI.