Quote:
Originally Posted by Ironduke
The first one of those four burned out in September 2007, after about 27,000 hours of use. The other three are still good, and have clocked up over 30,000 hours, as are the ones in his desk lamp and bathroom.
|
There is another issue regarding life expectancy. All lamp types suffer light loss over a period of time. This is certainly true with any fluorescent lamp. Cathodes erode and the phosphor coating gets "tired". Light loss on a typical, good quality CFL is a 20% reduction at mean output, which is generally at about 40% life. So, after about 3,200 hours on a 8,000 hour lamp, its light output is only 80% of what it started at. This is pretty good, but it gets much, much worse as time goes by. So, a lamp that is still burning many thousands of hours after its rated life is no longer efficient and should be replaced. More importantly, it simply is not doing its intended job and the lighting environment is very poor. I bet replacing those "good" lamps with new ones will have pretty startling results.
This situation is rarely a problem with incandescents since they normally have the decency to completely fail before lumen depreciation gets too low. The all time winner for the "lamp that refuses to die" award is mercury vapor. They typically have a rated lamp life of 24,000 hours, but it is not uncommon for them to last 50-60,000 hours. G.E. has shown that in those cases, output can drop to only about 10-15% of their initial output. Since the owner sees that the lamp is still burning, he or she thinks that it is still good; however, it has become a money pit that is not producing needed illuminance levels. It is the same for fluorescent, just not as dramatic.