There's a couple of reasons: * There's some evidence that light is useful for the biological process of waking up and keeping people wakeful in the morning. An

There's a couple of reasons: * There's some evidence that light is useful for the biological process of waking up and keeping people wakeful in the morning. Anecdotally, if it's a particularly cloudy day when I wake up, I am far slower to get going in the morning versus if it's a very sunny day. * If you live in a region that is afflicted by snow and ice in winter, you want the sunlight to help with warming up pavement and melting snow and ice [in conjunction with road salt]. This use in particular isn't solved with artificial light.