Vitamin D
What vitamin D has to do with sleep, mood, and energy — how you make it, why most people run low, and realistic ways to get enough.
Our databases
Measured, not guessed
We test every product ourselves: spectrum, lux, flicker and more. The data is free to use.
- SAD Lamps Tested for m-EDI, lux, glare and spectrum 57lamps tested
- Blue Blockers Spectral transmission data for every lens 61glasses tested
- Smart Lights Circadian-tunable lights for home setups 120lights tested
- Light Bulbs CRI, R9, color temp and flicker, every bulb measured 100+bulbs tested
- Night Oximeters Overnight oximeters, filtered and sorted 18oximeters tested
Our reviews
Ranked and explained
Hands-on best-of picks, backed by our own measurements.
See all reviews- SAD Lamps The few SAD lamps that earn their price 9ranked picks
- Blue Blockers The pairs that filter what they claim 10ranked picks
- Sunrise Alarms The wake-up lamps worth the price tag 4ranked picks
- Light Bulbs Healthy full-spectrum bulbs we'd buy 5ranked picks
- SAD Glasses Light therapy glasses that earn it 3ranked picks
- Circadian Rhythm How light sets your body clock
- Blue Light What it does after dark
- Full-Spectrum Lighting Indoor light closer to daylight
- Vitamin D Sun, UVB lamps and levels
- Sleep Environment Light, sound and air in the bedroom
- Sleep Position Back, side and zero gravity
- Breathing Nasal breathing at night
- Books The reading list behind the site
