I don't know if it's really ten lumens though.. But nevertheless it is a bright little light!
I guesstimate they really are about 10 lumens, but only on fresh cells. Of course, like most button cell lights, that outupt starts declining immediately after turn on.
It'll probably decline to 5 lumens after 30 minutes of constant running, then decline much, much more slowly down to 1 lumen over several hours of constant running.
Even 1 lumen from a keychain light can still be useful - probably enough light to walk a trail in a pinch.
However, when the output gets that low you might want to think about putting in some fresh cells - unless you're a really cheap smurf like me. ;>
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