Well the 50,000 hour ratings are guesses based on a heat soak test. They run the 24/7 in a heated room around 85-90*C till they fail. Then calculated back to math out the average life.
We have some LEDs that last 100,000 hours that run 12 volts. The problem is they are not quite as bright in the light they produce. When you start to jamb the power to them and over clock them you need a large heat sink like an aluminum block or finned rad to cool them. Leaving them on 24/7 is harder on them and will degrade their life much faster because they can't get rid of the heat and will cook the nanocrystalline, the little yellow part of the led that glows making the light.
Our company has found that it is better to run with the strength with numbers theory. We do not over clock our leds keeping the heat down but lighting up 3X as much nanocrystalline material increasing the life span and the amount of light. Then we can only make special lights that allow us the room to do this. Our warehouse light and street light retro fit are the best on the market for cost, life, light spread, and light produced. The picture is our 40 watt light in a cobra head street light.
Ocean Clear L.E.D. Solutions
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Cheers Don.