To avoid harm to the eyes.

Blue light is part of the natural light wave. But while the light blue spectrum of the sun has long wavelengths due to the distance of the Earth's atmosphere, it is unlikely that the blue light emitted by the screen can be displayed at higher frequencies. Blue is not dangerous. But exposure is too long, such as by touching a smartphone screen. The use to create a clear screen under the sun has been widely studied recently to gather or exclude connections with early onset of lenses in the lens, such as cataracts. Inflammation of the eye and cornea.