The common recommendation when looking for sunglasses is to find a pair that blocks 100% of UVA/UVB radiation or offers 100% UV 400 protection. The advice is simple enough. However, this then begs the question, what is the difference between the two? Is one better than the other?
What is UVA and UVB?
The sun emits 3 types of UV waves - UVA, UVB and UVC. Both UVA and UVB make it through to the earths surface. UVC (the most dangerous) on the other hand is mostly absorbed by the earth's atmosphere.
95% of UV radiation that makes it to the earth is UVA (this is also what is used in tanning beds). The other 5% is UVB (which is what causes most sunburns). Both types of radiation have been found to cause damage if directly exposed to our eyes.
This is the reason most experts will tell you to look for sunglasses that block 100% of UVA and UVB rays.
What is UV 400?
Simply put, UV 400 means that the lenses will block Ultraviolet (UV) waves shorter than or equal to 400 nano-meters (nm). All UV waves come in different lengths as shown in the chart below.