Agreed, Arnauti, but if you've ever camped out above the Arctic Circle in mid-summer, few native English speakers would say either of those things to describe the experience, partly, I would argue, because "bright night" could be construed as "starry". It would be more natural to flip it around and say "In summer it doesn't get dark at night" or something like that. (I am not suggesting this as a solution for the exercise!) Perhaps "In summer it/there is still light at night" comes closest to the Swedish.
The problem here is that using 'light' by itself to refer to a high ambient light level without a physical location qualifying things is not idiomatic English (at least, not idiomatic American English, and I've never heard any Australians or Brits using it in this way either). 'light outside' (or the clipped equivalent 'light out') instead of 'bright' would work here and be idiomatic, but without the location qualifier it sounds strange when talking about a period of time being 'light' in the 'not dark' sense instead of the 'not heavy' or 'not intense' sense.