However, at some point in time, exactly half of the bulbs will have failed. Follow me?
When this has occurred, you have reached a point of mean lamp life, a value somewhat longer than the manufacturer will claim for mean lamp life. … so if half the lamps burn out after 500 hours and the manufacturer says lamps last 450 hours, then you will experience that the lamps you buy usually last longer than the manufacturer claims. Good marketing. Not a reliable predictive value for the life of any individual lamp, however. that doesn’t mean that all the lamps will not have burned out after 501 hours or that one won’t burn out two minutes after you turn it on. It is not a point on a curve. In a perfect situation where the lamp is never subjected to any temperature swing, vibration and/or voltage variance, the lamp would burn for 750 to 1000 hours before burning out. But because lamps are rarely used in this perfect situation, outside events and elements tend to excessively flex the filament and can eventually break it. The lamps may be installed in a location commonly subject to
