Nokia T21 user guide

Blue light is a color in the visible light spectrum that can be seen by the human eye. Of all the colors that the human eye perceives (violet, indigo, blue, green, yellow, orange, red), blue has the shortest wavelength and thus produces a higher amount of energy. Since blue light passes through your eye’s cornea and lens before reaching the retina, it may cause itchy and red eyes, headaches, blurred vision, and poor sleep, for example. To limit and reduce blue light, the display industry has developed solutions such as the Low blue light mode. To switch on the Low blue light mode on your tablet, tap Settings > Display > Night Light > Turn on. If you need to look at your tablet’s screen for a long time, take frequent breaks and relax your eyes by looking at distant objects.

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