From Forever Fat Loss by Ari Whitten:
"1. Deficiency in sunlight exposure during daylight hours. We need sunlight for numerous reasons, like making vitamin D (from the sun‚Äôs UV rays), stimulation of cellular energy production (largely from light in the red wavelengths), and melatonin suppression (from light in the blue wavelengths). Sunlight is bioactive! It affects numerous aspects of our physiology and is an essential requirement for health. The deficiency of red and UV wavelengths can result in deficient cellular energy production and the problems associated with low vitamin D, but as sleep and circadian rhythm are concerned, the big problem is blue light. Blue light is what the circadian clock is wired to respond to. Why? Because the only time an organism was exposed to light in the blue wavelengths (prior to the invention of electricity), was from the sun‚Äî particularly around midday. You know, like bright sun and the blue sky. If blue light photons were entering the eyeballs and feeding back into the brain, that meant that the sun was up and it was time to be awake. So what happens when you spend all day indoors (as many of us in the modern world do)? Well, we do not get enough of the stimulus that tells our brains ‚Äúthis is daytime, the time to be awake,‚Äù and melatonin (the hormone that should be suppressed during daylight hours) is not adequately suppressed."
Light is also necessary to improve blood glucose. It helps "sulfate" cholesterol which causes it to go in to cells where it belongs rather than staying in the bloodstream. (not sure about this, I just started reading about it). When you get sun in the morning, it signals something in the pituitary gland which has an effect on hormones when you sleep at night. (According to Jack Kruse). It seems to have an appetite suppressing effect.
Morning sun contains red light which is anti inflammatory. It's probably anti-aging, and if nothing else helps balance whatever blue light there is. After noon blue light predominates which we already get too much of because of fake lighting, computers etc. If you go outside after noon it's probably not a big deal, but it doesn't do anything to help beyond keeping you alert and awake, which you already are. Blue light is aging and damages the skin and eyes (and probably every cell in your body), so there's reasons to avoid it.
If you can't get morning light, you could always buy a red bulb but I've read it has to be pressed on to the skin to make a difference. You could buy something like the Light Stim or a DPL which can be pressed on to the eyes and entire face:
I avoided sun a lot the last ten- 15 years. I have a lot of mid-life health problems because of it. I walked for years in the late afternoon thinking I was avoiding UV, but never felt better and couldn't figure out why. I was so tired I couldn't get out bed a lot of days and became a zombie. On good days now I wake up before the alarm at 5:30 and for a while this winter I slept through the night without getting up. I only use food and a few supplements (selenium, zinc, b vitamins, aspirin, salt, coconut oil, calcium, progesterone cream)currently; I'm not on thyroid. I get 15 minutes- 2 hours of sunlight before noon daily.