Children need to spend around three hours per day under light levels of at least 10,000 lux to be protected against myopia. This is about the level experienced by someone under a shady tree, wearing sunglasses, on a bright summer day. (An overcast day can provide less than 10,000 lux and a well-lit office or classroom is usually no more than 500 lux.)
Here were I live, we do not get almost any direct sunlight from October till March - sun is just too low and it is cloudy most of the time.
Another problem is the light levels in the offices that are not optimized for the good sight but for the least allowed energy consumption.