It would be interesting to see more research that breaks out sunlight exposure as an independent variable. There is some reason to suspect that we need both physical activity and sunlight for optimal effects.
I've noticed a significant shift in my mood during June, July, and August, which aligns with those sunny days. My mood changes from "okay" to "fantastic," and I've been tracking this shift year over year. The combination of physical activity and sunlight exposure certainly seems to have an "amplifier effect" on overall well-being.
Of course, I'd prefer advances in construction that would allow large amounts of full spectrum light to enter buildings, but that's only relevant to new construction.
https://www.ted.com/talks/richard_weller_could_the_sun_be_go...