Helsinki is up north. Most people probably know that. In fact, it is the northernmost capital of all EU member states and on the second place in the world ranking, being only beaten by Icelands Reykjavík. Here is a map putting into perspective just how far north it actually is. Flensburg, as the northernmost city in Germany does barely make it into the frame.
And with 60 degrees northern latitude, Helsinki is pretty much the southernmost point of Finland. The country spans all the way up to 70 degrees and therefore almost half of it lies above the arctic circle. Being that far north has the implication that the amount of variance in the length of the day over the seasons is significantly higher than in Central Europe. The length of a day in Helsinki varies between almost 19 hours in the summer and not even 6 hours in winter. That means that in December the sun does not rise before 9am and starts setting shortly after 3pm. All of this can be seen in this nice sun graph, where yellow represents daylight, red dusk, blue dawn and grey darkness.
And just for fun and because the graphs look so nice, here is one for northern Finland.
The missing daylight in winter can negatively influence motivation and mental-health. I personally am also noticing that when it is dark at 4pm it is harder for me to motivate myself to get some more work done. However, the Finnish medical system and society, as far as I can tell, focusses way more on mental-health than in Germany, going so far that e.g. at university there are information events at university about the topic of winter depression and easy to find pointers to services where you can find mental-health support. In addition to that, taking vitamin D supplements is very common, since the amount of sunshine in Finnish winter is not enough for the body to produce the required amount of vitamin D based on the UV radiation. I could try to summarize some facts about vitamin D supplements, however this has just recently been done by maiLab in a way more detail that I could have done it (unfortunately only in German, but I really recommend watching it if you understand it).
One last thought about sunshine in Finland: As I could just realize again today, if the sun does actually come out in the winter (which due to clouds is even rarer than just based on the northern location) it is a beautiful country. You can find some new images of the first snow of the season in the gallery.
I am the light of the world. Whoever follows me will not walk in darkness, but will have the light of life. — John 8:12