Canadian winters are dark, and my living space doesn’t get as much natural light as I’d like during the season. Working from home gets a bit depressing! I have a vague sense that things should be brighter. But how much brighter?

The quantity in question is lux - the intensity of illumination on a surface. For seasonal depression, the “surface” you probably care most about is the back of your eyeballs.

The standard regimen for treating seasonal depression is to get a dose of 10,000 lux sustained over 30 minutes each day. This is just a minimal treatment that is effective for most people; other variations may work just as well or better. According to lumenator folklore, different people experience different dose-response to light so you may want to experiment with even brighter doses or longer sessions, even if you already feel fine.

I have seasonal depression but I also get headaches with too much bright light, so I’ll need to thread the needle on this.

Measuring lux

Lux is different from how bright something looks. Our eyes and brains are constantly adjusting levels so that we can see clearly, so it’s impossible to judge lux based on your subjective impression. But luckily, it’s easy to measure with a smartphone.

I did exactly that, in various places around Toronto this winter! I learned some things, and other things I already “knew” were reinforced in a slightly more visceral way.

This was a very easy experiment to run, so I would recommend trying it yourself! You could download an app and take a measurement literally right now. I personally used the free Lux Light Meter Pro but there are many others which work in a similar way. I want to shout out Jenn’s lumenator article for making me aware that I could be measuring lux (literally right now).

Anyway, here are some things I learned from taking a lot of lux measurements.

Most artificially-lit locations are extremely dim

This may be obvious if you are into film photography, but it was not obvious to me.

At night, different parts of my house (which each feel comfortably well-lit) gives me 30-70 lux. That is a tiny amount of lux!

Public spaces that feel bright, like the inside of a TTC subway car (100 lux) or a windowless medical office (150 lux) are better but are still extremely dark on the grand scale of light therapy.

Daylight is extremely bright

When I’m out in the middle of the day, I generally get readings in the range of 1,000 - 10,000 lux. Even on a partially-cloudy winter day, I get up to 6,000 lux when walking in an open area at noon. If I point my phone toward the sun on a sunny day, it reads over 100,000 lux!

In indoor spaces with windows, measurements during the day are mostly dominated by (1) how close I am to a window and (2) how much sky I can see through that window. Facing a first-floor window I measured 100 lux, but facing a 20th story window with no nearby obstructions, I measured 1500.

Unless you are trying (and succeeding) to get more lux indoors, your interior lighting probably does not compare to spending more time outside. This is not to say that you won’t succeed, but rather that you should probably measure lux to make sure that you are having the intended impact.

The other implication is that taking a midday walk outside will give you a pretty respectable dose. Depending on your situation, that may be a much easier, cheaper and less annoying way to get lux than fiddling with your lighting at home. But as a wise person once said, why not both?

Lux drops off rapidly with distance

Okay, I knew this in theory, but it was still helpful to see this born out in the measurements.

Because of the physics of light and the way lux is defined, lux has an inverse-square relationship with distance from a normal light source. So if I position my LUXOR lamp a foot away from my face, in theory I get 10,000 lux, but at 2 feet I would only get 2,500. Actually, when I measure it it’s more like 6,089 and 1,788 - this may be my lack of calibration, the fluorescent bulb slowly warming up, or maybe the lamp isn’t delivering what it promised, but the measurements are at least self-consistent.

You can buy an extremely bright bulb, but if it’s even a meter away, you might not be receiving a lot in terms of lux (although maybe it still contributes to your room looking nice, which you might like anyway).

The other handy implication is that it’s easier to brighten a room if you have a lot of light bulbs that are distributed throughout - these sources are additive, and having them throughout the room means you are (probably) never too far from a light source.

Lux is very sensitive to where you are looking

When measuring with my phone, the results depend a lot on where I point the sensor. Outside, it’s about how much sky (or sun) is visible. Inside, if I’m standing in front of a 20th story window, I get 1500 lux when facing the window but only 150 when looking perpendicular to the window. And obviously, looking at a light bulb will expose you to more lux than looking at a wall illuminated by that same bulb.

When measuring with my phone, even small changes in angle can create large changes in the observed lux. This may be an artifact of my phone’s sensor though - the eye has a very wide field of view, so the exact angle may not matter as much to a person. But it’s something to be aware of if you are taking casual measurements with your phone.

~

This exercise confirmed my original suspicions: from a seasonal depression perspective, working from home is especially depressing in winter, when my house doesn’t get as much natural light, and I also tend to spend less time outside.

At the same time, the solution feels more tangible and achievable than ever. I can buy more and brighter lightbulbs until the lux goes up, I can take more walks, and yes, if it comes to it, I can even commute to the office.