I notice huge improvements in my well being and energy levels spending time in the sun without much clothing on, even in the winter when there isn't enough UV f

I notice huge improvements in my well being and energy levels spending time in the sun without much clothing on, even in the winter when there isn't enough UV for Vitamin D production. I suspect there are many other benefits to sunlight other than vitamin D, and that the modern advice to avoid the sun and supplement D instead has been a huge mistake. In addition to what you mentioned about "mitochondria need infrared," I've also seen at least three additional mechanisms: (1) We need bright sunlight for proper circadian rhythm, e.g. people in darkness experience disregulated sleep and ~26 hour waking periods. (2) Sunlight lowers blood pressure by producing nitric oxide. (3) Sunlight is necessary to regulate the dimensional growth of the eye, to prevent nearsightedness. I suspect there are many more than this also. I doubt that regular incandescent lamps have enough infrared to compete with natural sunlight or satisfy our biological need for infrared. People that do 'red light therapy' often use high wattage heat lamps close to the body without clothing or other barriers.