Lighting needs to consider circadian rhythms and how people are impacted by light in the built environment, confirms a new study released on Frontiers. The report shows that 248 scientists, with a total of 2,697 peer-reviewed publications on light and circadian clocks since 2008, reached consensus on 25 statements about the impact of light on circadian rhythms and health based on accumulated scientific evidence. In short: How we light our built environments needs to change.
A brief history on light
Since the beginning of time, humans have relied on the sun to dictate patterns of daily life. Bright daylight (10,000 – 100,000 lux) signified the start of waking, active hours. As evening and night-time came along, those numbers significantly dwindled (0.0001-0.1 lux). But modern lighting has in fact flipped things around, with electric light typically 100 times dimmer in the day than natural light and 100 times brighter after dusk than the brightest moonlight.
The research, conducted by Moore-Ede et. all, drew on authors who had 4 or more scientific peer-reviewed articles covering the topics of ‘circadian’ and ‘light’. Forty statements about lighting were then designed and emailed to the authors.
Consensus 1: Bright daylight supports circadian rhythm and boosts health
The first set of statements related to the role of bright light and daytime lighting on circadian rhythm. There was strong consensus that robust circadian rhythms are important for health (95.1%) and that disrupting circadian rhythms can cause ill health (98.4%).
There was also consensus that increasing daytime light intensity indoors within the normal indoor intensity range of 50–500 lux enhances circadian entrainment and strengthens circadian rhythms (70.5%), improves daytime alertness and reduces sleepiness (74.7%). The majority (59.1%) of respondents indicated there was “good evidence” or it was “well established” that increasing indoor daytime light intensity enhances sleep at night, but this did not reach the two-thirds consensus level.
Consensus 2: Bright lighting at night has negative impact on health
There was strong consensus that increasing indoor light intensity at night increases the disruption of circadian rhythms (90.6%) and increases the suppression of nocturnal melatonin production (94.6%). There was also consensus that repetitive and prolonged exposure to light at night bright enough to cause circadian disruption increases the risk of breast cancer in women (67.6%), obesity and diabetes (74.7%), and sleep disorders (87.4%).
Consensus 3: Blue light is a major sleep disruptor
Blue wavelengths, which typically tell the mind its daytime but is now found in artificial lighting, was deemed ‘one of the most potent wavelengths for circadian entrainment’ (92.7%).
There was also consensus that “blue-enriched (460–495 nm) light in the evening (during the 3 hours before bedtime) disrupts nocturnal sleep more (70.3%), phase delays the circadian system more (75.5%) and disrupts circadian rhythms more (70.1%) than blue-depleted light at the same intensity. There was also strong consensus that exposure to 460–495 nm blue light at night suppresses melatonin production (90.6%) and disrupts circadian rhythms” (84.9%).
Consensus 4: Evening lighting should be different from daytime lighting
There was consensus that “light used in the evening (during the 3 hours before bedtime) should have as little blue content as practically possible” (82.5%) and that “the risk of circadian disruption during the 3 hours before bedtime can be reduced either by 1) dimming indoor lighting which may compromise the ability to perform visual work tasks, or 2) reducing the blue content of indoor lighting maintained at the intensity required for visual tasks” (72.0%).
While some questions did not evoke a complete consensus, there was overall agreement on 3 main statements:
- Increasing indoor light intensity at night increases the suppression of nocturnal melatonin production
- Exposure to 460–495 nm blue light at night suppresses melatonin production
- There is significant variation in individual sensitivity to light; therefore, circadian lighting should be optimised where possible using personalised solutions
Overall, the study points to the significant impact of lighting on our circadian rhythms, health, and wellbeing – a key lesson we should carry with us when designing the built environment.
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Sophie Crossley is our Content Editor. She has 5+ years of experience in comms with a focus on wellbeing, the built environment, and lifestyle.