Just because they are shining, does not still mean they are emitting uvb rays. No such thing as a "lifetime" bulb to my knowledge. As the other member stated, 6-9 months they should be changed if you do not have a UV meter because if you do not, you have no idea if they are bad. edit: I see what you are saying about lifetime. Sorry, I misunderstood. I guess you meant life expectancy.