In health terms, what constitutes well-lit?

How we can optimise our exposure to light throughout the day to protect our natural body rhythms.
21 March 2022

Interview with 

Tim Brown, University of Manchester


A woman sitting on a park bench watching the sunset


We've discussed the importance of darkness during sleep, but what about getting the light right too? That’s the thrust of a paper in PLOS Biology this week, which attempts to provide some expert guidance on appropriate light levels. Tim Brown is one of the authors...

Tim - Of course we do have regulations for how much light we should have in our buildings. These are all focused on providing enough light for us to be able to see, read, navigate safely, etc, but they don't take into account effects of light on our body function. Regulating our body clock, which is a really important determinant of our health and wellbeing and effects on our alertness. And actually the systems that regulate them in our body are quite different from the rod and cone cells in the eye that we rely on for vision. It's a completely different system and it needs a new way of measuring light.

Chris - So in essence, then we understood the science because research is like yourselves have been talking about the importance of light exposure to feeling good mood waking up in the morning, setting your body clock, getting over jet lag, et cetera. They've been talking about that for decades, but are you saying that it just hasn't made its way into the sort of workplace psyche, domestic psyche in a way that really needs formalizing and people need clear unequivocal guidance.

Tim - You are quite right that we've recognized this idea that we probably need to get more light during the daytime and less light in the evening for a long time. But the question has been, how do you put a number on that? And actually it's not just a question of agreeing for numbers, but really it was agreeing the proper way of measuring light, because as I said, it's a different system. As you can imagine, when you experience light, what you are seeing is a range of different wavelengths and those different wavelengths of light don't equally affect these systems. The importance of blue light is because actually the biological system that regulates these things has a light sensitive protein that's particularly sensitive in that short wavelength, blue part of the spectrum. There's been disagreements about exactly how we should measure that. One of the things that came out of our report, which is a consensus agreement across many experts working in this field from across the world, was a new way of measuring light, which is relevant to this system. We were able to formulate our recommendations in this new, more appropriate light measurement approach

Chris - Is one frustration that lighting technology has completely changed out of all recognition in the last two decades where you said light bulb to someone in the year 2000, that means something completely different in the year 20 you two where most lighting is now LED. We went through a phase of having compact fluorescence and people said they were disturbing their sleep. Are you able to make your regulations or your guidance kind of future proof in that respect?

Tim - Yes, because they're not tied to any particular lighting technology. Although what I would say is actually, although people have been worried about the idea that there's a big blue component in LEDs, you have so much more control over LEDs to the extent where you can now tune the different wavelength bands within it to produce a light of a particular property. And the upshot is that we can start thinking about having two different lights. They might visually appear identical. One would have a stronger effect on our body clock than the other, just by tuning the mixture of wavelengths that are present

Chris - Is the elephant in the room, though, you might go to enormous lengths to advise on how to build better offices, better homes, better bedrooms that illuminate people in a way that's gonna be more in sync with their physiology, the way their body's trying to work. But if they're sitting there deluging themselves in bright light from a screen, then they completely undo all the good work you're doing.

Tim - One thing I imagine is that actually, we now know that increasing the amount of light we see in the daytime has some kind of a protective effect against the disruptive effects of light later on. In that sense, making things better during the day helps. But I suspect that increasingly we'll see personal light monitoring devices, similar to the kind of things that many of us wear on our wrists. Now that tracks other aspects of our health.


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