SAD lights

It seems like everyone I talk to recently is thinking in the same direction: managing their seasonal affective disorder, or SAD. If you live in Estonia, or anywhere with a long winter, or maybe even the less sunny parts of California, you'll know what I'm talking about. If you don't, the TL;DR is that in winter you tend to feel less tired and want to sleep more, this is probably due to your Circadian cycle getting unanchored because you don't get enough light signal, and the obvious fix is just getting enough light.

You want to get the maximum amount of lumens (a measure of how strong the light source is), a high CRI (a measure of how accurately the light spectrum reproduces natural sunlight) and a high color temperature (roughly, whether it looks like white morning light or yellow evening light). You probably also care about cost and design / form factor.

The lumen part is actually a simplification. You want high lux -- the amount of light arriving in your eye per unit area. This depends on distance, diffusion, etc, and you can measure it with your phone (find a lux meter app from the app store). Typical commercial tabletop SAD lights are supposed to give you about 10,000 lux and be used for 30 minutes per day. If making your own setup, you can go lower with the lumens but make it convenient to use for several hours. You need to scale duration inversely with the lux.

For lumens/lux, aim for whatever setup works for you to get roughly 300,000 min x lux. (Fun fact: summer morning sun does that in 3 minutes!) For CRI, aim for 90+, ideally 95+. For color temperature, 5600K+, ideally 6500K.

For design and budget, make whatever trade-offs are appropriate for you. You can do full DIY (getting an LED chip, installing it on a radiator, getting a power supply, adding a diffuser, etc). You can get bulbs and string lights, or a floor lamp with lots of sockets. Or you can get everything in a well-packaged form factor if you buy professional videography lights: they have the exact same light requirements as you, and are sturdy and portable (even if less aesthetic than normal lamps).

My setup, after a large amount of research, consists of two Godox Litemons LA150D lights plus two tiny tabletop light stands. With these, I get:

  • 5,600K color temperature
  • 96 CRI
  • up to about 30,000 lm maximum illuminance

One sits on my work desk and diffuses from the white wall I'm facing. The other sits on top of a tall shelf and lights up the whole room with ambient light, and sort of looks like the sun up in the sky (I don't think this makes a big difference but I like the aesthetic!). Overall, I've measured this gives about 2,500 lux in my normal eye position. At that level I can comfortably sit behind my work desk for several hours with the lights on, and I usually run them for about 2 hours in the morning to get my light dose without catching myself squinting. (The only issue is that my laptop screen seems dim compared to the background!)

All of the above applies to get the morning/daytime lighting setup right. For the evening (when you want to get warm light), most of my home uses these IKEA bulbs that have adjustable color temperature but are still relatively warm compared to the morning lights.

I skipped all of the research, mechanisms, reasoning, and lamp options here on purpose. To get all of those, I recommend reading through LessWrong posts tagged "lighting" and following the links therein. This post is a good start.