Social, daylight or internal time?
We’ll be ‘springing the clocks’ forward to British Summer Time on the 29th of March, marking the shift to longer days after a long, damp winter – When do the clocks go forward and why does the UK observe Daylight Saving Time?
Along with the ongoing debate about whether these national experiments in jet lag should take place at all, clients often ask me whether a ‘proper’ circadian lighting system shouldn’t progressively adjust so that the light levels and CCT mirror those outside.
After all, our internal clocks are still locked onto natural daylight time, with reduced sensitivity to evening light during the summer compared to the shorter winter days – Seasonal Variation in the Responsiveness of the Melanopsin System to Evening Light: Why We Should Report Season When Collecting Data in Human Sleep and Circadian Studies. Interestingly, for those suffering from moderate depression, photoentrainment (the power of light to keep the sleep-wake cycle on track) is depressed regardless of the season, helping to explain the benefits of bright light therapy beyond the ‘winter blues’ – Circadian photoentrainment varies by season and depressed state: associations between light sensitivity and sleep and circadian timing, Bright Light Therapy: Growing Evidence Beyond Seasonal Depression.
But social and working times stay the same year-round, especially visible in 24/7 settings like airports and hospitals, with an estimated one in five adults working shift patterns to keep those essential services on track while we sleep – Associations between shift work patterns and sleep disturbance: an analysis of cross-sectional data from UK Biobank.
So what does that mean for the lights?
When it comes to the body clock, there’s growing evidence that ‘circadian-informed’ lighting (essentially creating an ‘artificial day’) can support the sleep-wake cycle and improve alertness – Lighting the path forward: the value of sleep- and circadian-informed lighting interventions in shift work.
And when it comes to visual comfort, safety and how spacious and comfortable we feel in a space, even on long summer days, only a fraction of those rays will penetrate further than a couple of meters into a room, with north-facing room getting up to 15% less light than a west-facing one – Daylighting assessment of window layouts and architectural elements in early design stages. High-quality, well-designed artificial lighting installations can help to balance the dynamic full-spectrum qualities of daylight with consistency and control – Investigating the Impact of Combined Daylight and Electric Light on Human Perception of Indoor Spaces, while integrating light-sensing ‘daylight harvesting’ controls will reduce energy use and meet new Part L regulations here in the UK too.
We live ‘unplugged’ from solar time, thanks to millions of unsung heroes working through the night to keep our loved ones and us safe while we sleep. My experience working in residential care settings, and the evidence from large-scale studies, suggests that circadian-aware lighting, set to a 12/12 solstice schedule, can help to chart a safe and sustainable path between solar, social and internal time.
Retail therapy for a lighting geek in Heathrow Terminal 5
Flight delayed – the perfect opportunity to mooch around the duty-free shops and food concessions with my light meter.
Fascinated to spot the difference between the basic tourist-bait and JD Sports stores and the premium fashion and whiskey brands.
Although, apart from the video advertising panels, the lighting was fixed, it won’t be long before the high-end brands are exploiting the latest research to create dynamic displays that adjust the colour rendering (range of wavelengths in a light source) in your peripheral vision. This subtle shift will change the pattern of your gaze. And where you look, you’re more likely to touch and then to buy – An exploratory study of retail lighting with continuous modulation of color rendering properties to influence shoppers’ spatial range of browsing, Exploratory Shopping: Attention Affects In-Store Exploration and Unplanned Purchasing.
Take a look at the lights next time you’re delayed.
Just don’t miss your flight!