It is lightest around the summer solstice on 21 June and darkest around the winter solstice on 21–22 December in the Northern Hemisphere. In London, day length swings from about 16 hours 39 minutes at midsummer to roughly 7 hours 50 minutes in midwinter. Below you can see when – during the year and during the day – it is lightest and darkest, and why.
The year peaks for light at the longest day of the year around 21 June. The sun is highest in the sky at midday and there are the most hours of daylight. In the weeks around the summer solstice the difference from day to day is tiny – the days «stand almost still» – before slowly shortening again towards autumn.
Note that the earliest sunrise and the latest sunset do not fall exactly on the solstice. The earliest sunrise comes a few days before 21 June, and the latest sunset a few days after. This is due to Earth's elliptical orbit and axial tilt.
It is darkest around the shortest day of the year at the winter solstice. There are the fewest hours of daylight and the sun stays low. After the winter solstice the days start getting longer again – slowly at first, then faster towards the spring equinox, when day length grows the most (up to 4–5 minutes per day).
On a daily basis it is lightest at solar noon, when the sun is highest. It is darkest in the middle of the night, as far as possible from solar noon. Between day and night lies twilight: in summer at high latitudes it never gets fully dark, because the sun does not drop far enough below the horizon.
To see exact figures for your location, use the calculator on the front page, check the solar calendar, or view the whole year in the year chart. You can also look up sunrise and sunset for your city.
It is lightest around the summer solstice on 21 June, the longest day of the year, when there are the most hours of daylight.
It is darkest around the winter solstice on 21–22 December, the shortest day of the year, when there are the fewest hours of daylight.
The earliest sunrise comes a few days before the summer solstice, and the latest sunset a few days after. This is due to Earth's elliptical orbit around the sun and its axial tilt, which shift solar noon slightly through the year.