First thing’s first: Look at the lenses themselves. “If you see that the lens is pretty much clear, even light yellow, it’s probably not blocking out most of that light,” says Banik. Best to opt for darker tinted lenses (think amber, orange, or even a deep red) to completely block out the blue light. That’s not to say clear lenses don’t help at all, but if you really want to up the ante, you might want to invest in a pair of ambers. 

If you do already own a set of clear lenses, though, Banik does offer another trick to tell whether the glasses actually do their job well: “Put them on, then look at your screen at something that’s blue. If you can still see that color blue, it means that it’s not really blocking the blue light.” On the flip side, if blue tones on your screen have an orangey hue, this means the lenses effectively omit the wavelength. 

We should note that you don’t have to necessarily block every single trace of blue light. Not all blue light is bad! It’s chronic exposure that will typically affect your sleep cycle by interfering with melatonin production. On the day-to-day, it ultimately differs from person to person: Some feel just fine with a little filtered light, while others need the full-on amber-tinted lenses in order to concentrate. “It’s really based on your comfort level,” says Banik. “But I can tell you when I wear my denser blue blockers, I definitely feel the difference.”

https://www.mindbodygreen.com/articles/functional-eye-doctors-tip-to-test-your-blue-light-glasses