So this seems REALLY unnecessary, and the answer may be blatantly obvious to most, but it's a preference that actually swings both ways shockingly enough.
So here's me; I work in industry, I get eye protection speeches jammed in through my ears constantly, I'm fully aware of risk, and more over, having been on a safety committee, I know what to look for in eye protection.
What do I look for when I'm shopping for new lenses?
1) Glasses or goggles?
What level of protection I'm comfortable with, and I'm okay with glasses.
***special note: glasses are made for dozens of different types of faces. If at all possible try on a pair of glasses before buying them. Even if it's someone elses glasses at a game. make sure the contours fit your face well.
FYI for European standards they go by CE and EN166. Simply being marked "CE" doesn't necessarily mean anything; they could just block 99% UVA/UVB.
EN166 has the actual letter markings denoted the ballistic protection of the glasses.
2) Safety rating! Z87.1+
Z87.1 is rated to just over 1 joule. It's specifically a dust shield. Keep in mind safety GLASSES have lower standards than safety GOGGLES. And this is going off the 2003 standard.
Z87.1+ is around 3-4 joules, "good enough" for airsoft under normal conditions, assuming everyone is obeying the joule limits.
After finally being able to find a full, completely copy of the Z87.1-2010 documentation (couldn't freaking find one a year ago for some reason), it seems that they're just using the deflection test as proof of high impact resistance. Couldn't find any evidence that they were still doing a high velocity impact test, but apparently the deflection test doubles as the high velocity impact test
CSA Z94.3
Section 229
(a) safety eyewear must meet the impact strength requirements of the CSA Standards listed – able to withstand the impact of a 6.4 millimeter diameter steel ball travelling at 46.5 metres/second.
0.982g at 152.5fps - 1.06j
Equivalent to Z87.1, and not nearly good enough for airsoft
If it's mil-spec rated;
MIL-PRF31013
3.5.1.1
Ballistic Resistance
The ballistic resistance of the spectacles shall be such that they will pass a Vo test using a 0.15 caliber, 5.8 grain, T37 shaped projectile at a velocity of 640 to 660 feet per second when tested as specified in 4.4.1.1.
MIL-DTL-43511D
3.5.10
Ballistic resistance. The ballistic resistance of the lenses shall be such that they will pass a V0 test using a 0.22 caliber, 17.0 + 0.5 grain, T37 shaped projectile at a velocity of 550 to 560 feet per second when tested as specified in 4.3.5.
**MIL-PRF-32432, CLAUSE 4.4.3.3.5, SUPERSEDING FORMER MIL-DTL-43511D, CLAUSE 3.5.10
Same test as above, with more impacts and requirements. (Thanks to docholiday for that one)
Test specifics here
Wherein a "T37 shaped projectile" is a
BULLET. And 17 grains is
1.1 GRAMS. At 550fps. That's about
15 joules of force for MIL-DTL-43511D, and 7.5 joules for MIL-PRF-31013.
Yeah, that'll stop a BB alright.
3) Documentation.
How do you know some chinese manager looking to make a quick $ didn't just use a mold with "Z87.1+" stamped in it and fill it with clear plastic? You know, because China has a reputation for doing shit like that.
Documentation means actual tests were performed, it means quality control, it means LIABILITY.
4) BRAND.
Okay some of you will think this is stupid. You can get a $5 pair of safety glasses that do the same thing as a $50 pair, right?
Where's that extra money go?
If it does turn out your $5 pair was just recycled paper bags, and it shatters in game and you lose an eye, what's your next course of action? Sue the manufacturer! Sue China? Yeah good luck with that.
***Also keep an eye out for REPLICAS. If you see a $140 set of oakley M-frames being sold for $30, chances are pretty darn high that they are fake. Good luck trying to sue oakley with a set of fake glasses.
5) More importantly, BRAND!
These people make thousands, maybe millions of lenses a year, and they can get sued or fined for hundreds of thousands of dollars for every single one that breaks. That's a lot of nerve wracking potential lawsuits out there.
I know soldiers wear the same lenses I have, day in day out, and I know some of them have seen how good the protection really is.
You never hear soldier say "Yeah those $5 princess auto glasses saved my eyes when our tank got hit with an RPG and it was like a frag went off inside!"
So obviously the minimum rating of your glasses needs to be at least 2.3 joules which is 500fps on .20s. That covers normal airsoft use.
There are some clubs that allow bolt action or other guns up to 600fps on a .20 (3.34j). You need to be aware that this is OVER the test limit for Z87.1+, and you should adjust your minimum eye protection requirements accordingly.
As well, there are some clubs that just don't chrono often or at all. We only chrono'd for fun back in the day, no one was ever required to chrono on a given weight of ammo. Be aware that some stock gas rifles, particularly 20" barrel length rifles, can shoot well over 500fps stock. I once clocked in a WE M16 at a whopping 570fps on .20s, just image what it would have shot on .36s... Figure it would have been well over 4.5j
There's also the occasional douchebag that wants to crank up the fps on their GBBR/P*/SMP/whatever.
So given all these unlikely, but very possible scenarios, I feel pretty safe having a minimum protection of 7.5j
Now the point of this is not to get you to run out and go buy a $50 set of glasses.
The point is to educate you so YOU can make that decision YOURSELF.
Either you're happy with $5 glasses that may shatter when hit and leave you screwed with a lost eye and nobody to sue. Or you feel safe in the fact your glasses are combat tested to protect you from high velocity shrapnel.