Indoor lighting tenfold less bright than sunlight. Bright light needed to make serotonin, needed to feel upbeat. UVA in sunlight sets local circadian clocks. Blue light sets master clock Shawn Stevenson: "Is the average person light deficient?" Dr. Alexis Cowan: "Yeah, I would say we're not only deficient in specific wavelengths of light that you would find within sunlight, in particular, UV and infrared, and red to a certain extent as well, but we're also deficient in total brightness. […] People may not know that serotonin is made in the pineal gland. Serotonin gives us feelings of connection, kind of, you know, feeling upbeat, feeling motivated in a different way than dopamine in some ways, but it's more of a social neurohormone that plays really important roles in how we move through the world. […] Its production is stimulated in the pineal gland in response to not only the right parts of the light spectrum, including UVA, but also total brightness is very important when it comes to stimulating beneficial neurochemistry that makes us alert, awake, able to learn, able to have an upbeat mood, etc. "If we're living an indoor lifestyle, most people aren't experiencing more than 10,000 lux of light at a given time. (Lux is a measure of brightness.) […] Bright light is really, really important for stimulating serotonin production in the brain. And if we're outside on a bright sunny day midday, we're talking upwards of 100,000 lux or more compared to the max around 10,000 lux that you would experience if you're in an indoor environment. […] A lot of people are walking around or living in indoor environments during the day that are around 1,000 to 5,000 lux. At best, you're looking at around 10,000 lux. Outdoors, if you're out on a sunny day or even a cloudy day, you're looking at 50,000 to 100,000 lux, so you're looking at a tenfold difference." Shawn Stevenson: "Holy moly. So, so many of us, especially not on a consistent basis, aren't getting bright light, period." Dr. Alexis Cowan: "Yep. Exactly. So, that's number one. The brightness of the light is a problem. "Number two is the spectrum of the light. […] Even just simply cracking windows, if you're able to do that, letting that full-spectrum light in is going to make a difference with regards to this. The UVA component of light is also really important. UVA stimulates a photoreceptor on our skin and eyes and other parts of the body as well called neuropsin. Neuropsin is specifically a UVA light detector. It is a protein receptor that's on our surfaces that's looking for UVA light. That's why I always kind of like laugh when I hear the dermatologists and ophthalmologists saying you need to avoid UV light at all costs when our bodies are literally coated with a UVA light-sensing protein that is looking for the stimulus to help set local circadian clocks. […] "Blue light through the eyes, […] and through our systems in general, is kind of what's telling our body what time it is. […] The back of our eye, the retina, is directly connected to a structure within the hypothalamus in the brain called the suprachiasmatic nucleus or the SCN. This is the master timekeeper for the body, the master clock. And so the blue light comes in through the eye, stimulates the retina, is propagated back to the hypothalamus to the SCN. That master clock gets set. It says, 'OK, based on the intensity of this blue light, it's XYZ time of day.' Then the downstream effects are we're basically telling the peripheral clocks throughout the rest of the body, 'OK, this is what time it is.'" […] "And I want to definitely talk about UVB light as well as well as red and infrared. […]" Dr. Alexis Cowan with Shawn Stevenson @ 08:27–12:29 & 14:10–14:13 (posted 2025-11-13)