Why getting enough bright light during the day is just as important as avoiding light before bed

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The main villain responsible for our poor sleep habits and wonky circadian rhythms, we’ve been led to believe, is too much evening screen time. Keep those pesky iPads out of the bedroom.

But as scientists learn more about how our biological rhythms are kept in sync, it’s becoming clear that the flip side of the coin – getting enough bright light during the day – is just as important as avoiding light at night. This has important implications for how we organize our work spaces.

In May, a new version of the WELL Building Standard, focusing on how indoor spaces affect human health, was announced. Launched in 2014 and overseen in Canada by the Canada Green Building Council, the WELL standard offers independent certification to buildings that meet standards relating to factors such as air, water, fitness, comfort and light. Canadian participants include the Toronto-Dominion Centre in Toronto and MNP Tower in Vancouver.

While office design has traditionally considered the importance of having enough overhead electric light to read and write properly, WELL also includes formal guidelines for what it calls circadian lighting. During the critical hours between 9 a.m. and 1 p.m., the guidelines suggest, you should be exposed to at least 200 “equivalent melanopic lux” to maximize your alertness and mood and keep circadian hormones such as melatonin in sync.

Making sense of this recommendation requires some background on how your eyes work. Your vision depends on the light-sensing properties of rods and cones, which are most sensitive to green-blue and green-yellow light. But there’s a third type of light sensor called “intrinsically photosensitive retinal ganglion cells,” or ipRGCs, that doesn’t help you see but detects light to synchronize your circadian rhythms. These ipRGCs are most sensitive to blue light.

As a result of these different light-detecting cells, brightness (typically measured in units of lux) isn’t the only lighting characteristic that matters. Instead, the WELL standard uses melanopic lux, which is adjusted to reflect how much light the circadian-linked ipRGCs are detecting. For example, they detect about 45 per cent of the light from a “soft white” LED light with a colour temperature of 2,700 Kelvin, and 75 per cent from a “cool white” LED at 4,000 Kelvin.

Figuring out whether you’re getting the recommended 200 melanopic lux from your monitor, lamps, overhead lights, windows and even light reflected from walls is far from trivial. At an industry conference last year, Martin Brennan and Alex Collins of Portland-based ZGF Architects LLP presented the results of detailed simulations of different office configurations to determine which factors made the most difference.

The key takeaway for office workers who don’t necessarily control their building layout, Brennan explained in an e-mail, is “customize your work station lighting to work for you.” A bright computer monitor and a lamp can give you about half the suggested melanopic lux. Adding free software such as f.lux can automatically tune the colour and intensity of your computer monitor throughout the day depending on your precise latitude, giving you the brightest light when your circadian rhythms expect it. It’s also possible to get task lamps with tunable LEDs that do the same thing.

If you do have a window, the best orientation will depend on your personal preferences, but Brennan suggests considering orienting your desk at 90 degrees from the window. This will minimize glare and hopefully reduce the temptation to shut the blinds when it’s bright out. Having neutral, reflective finishes on the wall can also make a big difference to your light quota, particularly in smaller rooms such as home offices.

Following all this advice still doesn’t mean that spending your evenings in front of a screen is a good idea. Still, it’s worth noting that a 2016 study by Swedish researchers, published in the journal Sleep Medicine, found that volunteers who read for two hours from a regular book or a tablet before bed showed no difference in sleep or melatonin levels – as long as they got 6.5 hours of bright light exposure during the day.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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