[postoak]

I'm guessing they aren't saying the light is necessary for school/learning, but that it is unknown whether it is needed for human development. Most of the time mammals and humans evolved they probably spent a substantial amount of time outdoors and if kids spend the majority of the day without sufficient light it could effect their development. Of course there probably isn't sufficient research to know, but it seems pretty clear that sunlight exposure affects sleep and mood which are pretty important for the brain to function well.