Great question. And this is critical.
Yellow lenses block blue light (400-480nm) but let other wavelengths through. They're perfect for daytime and evening use—protecting your eyes while working, but not making you drowsy.
Red lenses block blue light PLUS green spectrum (400-550nm)—the full range that affects melatonin. These are for nighttime only, 1-2 hours before bed.
Here's the problem: most people only buy one pair.
They either:
- Buy yellow and wonder why they still can't sleep (not strong enough for nighttime)
- Buy red and can't wear them during the day (too strong, makes you drowsy at work)