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This is: Why indoor lighting is hard to get right and how to fix it, published by Richard Korzekwa on the LessWrong.
The days are getting shorter in the northern hemisphere, and with the ongoing pandemic, most of us expect to be spending more time in our homes than normal. Creating a healthy home environment is more important than usual, and the light inside your home is an often underappreciated part of this.
There has already been some explicit discussion[1] about the importance of lighting for health and productivity, as well as many mentions of it in other places. Nonetheless, based on discussions I've had recently within the community, I get the impression that it is helpful for me to write up the results and tinkering that have done over the past few years.
First, I will cover some of the research on how our bodies respond to light, and which particular characteristics of natural light we want to mimic. Then I will explain solving this problem is hard and my overall strategy for solving it. Finally, I will give some specific advice on what to buy and how to arrange things.
I give quite a lot of background before offering any specific advice. Although I think the background information might help you make good decisions, you should feel free to skip the next section if you're in a hurry or if it seems uninteresting.
Background
Note: My background is in optics, not physiology or psychology and I began researching and writing this document almost four years ago. My original draft, as well as many of my sources, have been lost in the intervening years, so what you're seeing here is based on a combination of my notes that survived, my recollection of the research, and a partial duplication of the research. To make matters worse, it does seem that new research has come along since I began this project, so this is likely out of date. My guess is that most or all of the practical conclusions still stand, but I am only moderately confident of this. As much as I would like to take the time to update the research, past experience suggests that I will never actually publish it if I try to put too much more work into it. I welcome corrections, and if there is sufficient enthusiasm around this topic, I may try to write an updated version.
Your body uses light to synchronize its internal clock and to modulate your mood and alertness[2]. While the particulars of the lighting in your environment are important, your only perceptual access to information about lighting in the moment comes from your visual system, which is poorly adapted to solving the problem of determining the intensity and spectrum of a light source. This is mainly because our vision is optimized more for accurately identifying materials, textures, colors, and other properties of our surroundings than it is for knowing details about sources of light. This has the consequence that some of our default intuitions about the nature of ambient light are wrong, so when we're building our lighting environment, it can be difficult to make accurate judgments just by looking at things. We can do better if we use quantitative measures and our scientific understanding of how things work to solve the problem.
Physiology
In addition to visual photoreceptors that are used for seeing things, your eyes contain non-visual photoreceptors which serve non-visual functions. Melanopsin is a photopigment that is found in cells in the retina[3]. It is sensitive to blue light, and when activated, these cells send signals that help with things such as regulating our internal clocks[4]. Unlike the our visual photoreceptors, which are more densely packed in the center of our retina[5] than in the periphery, these photosensitive cells are distributed relatively evenly throughout the retina[6], so that light coming from both the periphery and the cent...
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