How much daylight do you actually get in Sweden in winter, and what do you do with the evenings?

How many hours of daylight do you get where you live?

The table shows the time between sunrise and sunset, calculated with NOAA's solar equations for six Swedish cities. On 21 December the sun rises in Gothenburg at 08:54 and sets at 15:26. In Stockholm it is down by 14:48, in Luleå by 13:04. North of the Arctic Circle it does not clear the horizon for weeks.

That is what the sky offers. What the eye actually receives is another matter, because most of those hours are spent indoors, behind windows, in offices and in front of screens. And that is where the research has something to say.

How much light does the eye need by day?

In 2022 an international expert group, including Brainard, Cajochen, Czeisler and Lockley, published consensus recommendations for indoor light in PLOS Biology. Their measure is melanopic EDI, light weighted by the sensitivity of the eye's clock cell, as defined in the CIE S 026 standard. The daytime recommendation is at least 250 melanopic lux at the eye, measured vertically at seated height, and daylight should be used first to get there. How the clock cell works is covered in Your eye's third cell type.

Ordinary room lighting often sits far below that. In one of the studies the recommendations draw on, standard 4000 K lighting gave about 100 melanopic lux. Daylight outdoors gives far more, even on an overcast winter day, which is why the expert group puts daylight first.

The 2013 camping study in Current Biology shows the same thing from the other direction. Electric lighting and the built environment went together with less sunlight by day, more light after sunset and a later internal clock. After a period of natural light only, the clock lined up with the sun: the biological night began at sunset. What that means for the evening lamps is in Firelight is orange.

Why is the morning the hour that matters most?

In the camping study the clock settled so that the biological night ended just after sunrise, before waking. That is the order winter disturbs. On 21 December the sun rises at 08:54 in Gothenburg and 09:55 in Luleå, long after most people have started the day indoors, and the first hour of daylight lands behind a window or a screen. The recommendations do not solve that for you, but they point the way: the 250 melanopic lux should come from daylight first, and there are only a few hours of it to collect. A walk at lunch, when the sun is at its highest, is the simplest route there.

What happens in the evening when it is dark at four?

The same expert group sets two evening targets: under 10 melanopic lux for the three hours before bed, and under 1 lux in the bedroom. In December that means an evening that starts just after three in Gothenburg and runs for six or seven hours under lamps, the TV and the phone.

The light from those sources sits in the middle of the clock cell's band. When Brainard and colleagues mapped its sensitivity in 2001, 446 to 477 nm was the most potent region, and that is the part an orange or red lens removes. Orange · Evening filters 98% of blue light between 400 and 500 nm, Red · Night 99% of blue and green light between 400–550 nm. Whether the room then ends up under 10 melanopic lux depends on the lamps. We have measured lenses, not rooms.

Does a yellow lens help by day in the winter dark?

No, and that needs saying plainly. Yellow · Day filters 95% of light between 400 and 500 nm, which is exactly the band the daytime signal is made of. It is meant for the screen hours at the desk, not as a substitute for daylight. If you want the day's signal, it is outdoors in the morning without glasses, for as many minutes as you can get before the sun goes down.

Winter in Sweden is therefore two different jobs. The day is about getting enough light, and no lens solves that. The evening is about removing the blue, and that is what the lenses are built for. Which tint suits which hour is in Yellow, orange or red lens.

What does a winter day look like in practice?

• Morning: out into the daylight without glasses. In Stockholm on 21 December that is between 08:43 and 14:48, in Gothenburg between 08:54 and 15:26.
• The screen hours: a yellow lens if you like, but it gives no light. Sit by the window.
• From sunset: the orange lens, and the lamps turned down. The target is under 10 melanopic lux for the last three hours.
• The last two hours: the red lens, and under 1 lux once you are in bed.

The whole evening, hour by hour, is in The Evening Routine. The winter protocol for the darkest months is in Winter Arc.