Probably a dumb Q about exposing LO to sunlight

EvenAngelsFall

I had read in a couple places that it's good to expose LO to the sun's rays first thing in the morning, and again in late afternoon, to help them distinguish day vs. night.

My (probably) dumb question is: you don't have to bring LO OUTSIDE to do this, do you...? Is standing in a sunny window with him enough? Does some kind of cruscial element get filtered out through glass? Its way too cold in the northeast to be bringing him outside twice a day!