How much is a day in sun?

I'm curious to know, just how much value does a day basking in the sun really hold? Is it measurable in terms of vitamin D production, mood elevation, or perhaps even the simple joy of feeling the warmth on one's skin? Are there any tangible benefits that can be quantified, or is the value purely subjective and intangible? I'm eager to learn more about the potential benefits of spending a day in the sun and whether or not they can be quantified in any meaningful way.