I think it must be something more to it than only the sun. I have lived north of the arctic circle in the land of the midnight sun (Norway) most of my life, potatoes and carrots grown here are not bigger than what is grown in the south where the growing season is much longer.
the part of Europe inside the Arctic Circle where the sun is in the sky very late at night in the summer.
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Collins: Land of the Midnight Sun
in American English, noun.
1. any of those countries containing land within the Arctic Circle where there is a midnight sun in midsummer, esp. Norway, Sweden, or Finland
2. Lapland
in British English, noun.
1. any land north of the Arctic Circle, which has continuous daylight throughout the short summer, esp N parts of Norway, Sweden, and Finland
2. an informal name for Lapland