Light that is brighter than is possible inside most homes makes you more alert (almost immediately), and if done during the first 3 hours of wakefulness has benefits that last throughout the day according to Andrew Huberman.
Specific qualities present in sunlight when the sun is very low in the sky (or under the horizon, namely yellow-blue contrasts detected by the intrinsically-photosensitive retinal ganglion cells) entrain the body's clock, making it easier to get to sleep at a consistent and suitably early time of day.
UVB exposure triggers a skin-brain-gonadal axis through skin p53 activation (nothing to do with vitamin D). I.e., 20 or 30 min every other day of strong sunlight on bare skin and into your eyes increases your levels of the sex hormones.
Certain red and infrared wavelengths help cytochrome c oxidase turn serotonin into melatonin, which is a potent antioxidant right where antioxidant activity is most needed (in the mitochondria).
What's the fifth one?
ADDED. It just occurs to me that with "I know 5" the conversation might have jumped from the object level to a comment on the social and emotional effects of my comment. D'oh!
They seem a bit remote for someone at high risk of skin damage due to skin type and location. I am surprise the immune system does not get more attention in discussions like this. I would put it high on the list.
There is an interesting wtf correlation between incidence and severity of multiple sclerosis and latitude. Sunlight (or alternatively narrowband UVB in a controlled clinical setting) can be an effective treatment for some skin conditions.
