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Your sunlight wavelength cheat sheet ☀️ ⠀ UVB (280 to 315 nm) • Makes vitamin D in your skin • Builds new melanin, your lasting tan • Triggers beta-endorphin, the feel-good hormone • Only shows up when the sun is high, around midday ⠀ UVA (315 to 400 nm) • Releases nitric oxide from your skin, relaxing blood vessels and lowering blood pressure • Pulls existing melanin to the surface, your quick glow • Shows up about an hour after sunrise and sticks around all day ⠀ Violet (about 380 to 420 nm) • Picked up by a light sensor at the front of your eye called neuropsin • Linked to healthy eye growth in kids • Mostly missing from indoor lighting ⠀ Blue (about 450 to 490 nm) • The main signal your body clock reads • Boosts alertness and mood during the day • Pushes back melatonin at night ⠀ Yellow and orange • At sunrise and sunset, your eyes compare them against the blue sky • That contrast tells your clock what time of day it is ⠀ Red (about 620 to 700 nm) • Supports your mitochondria, the energy makers in your cells • Works best in the morning • Dominant at sunrise, with almost no UV ⠀ Near-infrared (700 nm and up) • Penetrates deep into your body, even through your chest • Together with red, it makes up more than half of sunlight • There all day, even when it's cloudy ⠀ Every one of these comes free in sunlight, all at once. ⠀ A lamp gives you one or two. The sun gives you the full set.

Bright light in the morning raised people's cortisol by more than 50%, almost instantly. The same light in the afternoon did nothing. ⠀ Here's the study. ⠀ Researchers kept 8 healthy men awake through the night, in dim light, and measured their hormones every 15 minutes. Then they changed one thing: ⠀ • In one version, the men got 3 hours of bright light early in the morning, from 5 to 8am ⠀ • In another, they got the same bright light in the afternoon, from 1 to 4pm ⠀ • In the third, they stayed in dim light the whole time ⠀ Here's what the morning light did: ⠀ • Cortisol jumped by more than 50%, right away ⠀ • Melatonin, the sleepy hormone, got shut down ⠀ • And even after a full night with no sleep, the men stayed noticeably more alert ⠀ The afternoon light? No effect on hormones or alertness at all. ⠀ A separate study backed it up. Men exposed to bright light right after waking had about 35% more cortisol in the first hour than men who woke up in the dark. And the same light in the evening didn't change cortisol at all. ⠀ That's the key: timing. Your body is primed to respond to light in the morning in a way it simply isn't later in the day. ⠀ Cortisol gets a bad rap, but that morning spike is your body's natural wake-up signal. It's what gets you out of grogginess and sets up your energy for the whole day. ⠀ So the most powerful sunlight of your day might be the first sunlight of your day.