There are a lot of discussions in the lighting forum of Garage Journal that compare different sources of light. You will see discussions about lighting performance comparing lumens, color, CRI, beam angles, reflectance, lux and all sorts of other lighting science that may or may not have any relevance to a shop or a garage space.
One thing that you will often see compared is the life ratings of various lighting products. Average Rated Life numbers get thrown around alot in conversation but I bet that most people outside the lighting industry dont really understand what those numbers mean.
This is my attempt to explain it to the members of GJ, using plain english.
When a manufacturer states that a lamp's life is "X" hours, what does that mean? Does it mean that when the lamp gets used that many hours it will die? How do they know this? How is it possible for an LED manufacturer to know that his lamp will last 50,000 hours when it was only invented last week?
Let's look at a typical F32T8 lamp, which is commonly discussed on this forum. The run-of-the-mill T8 lamp has an Average Rated Life of 24,000 hours. The life testing is done in a laboratory environment. A sample batch of the lamps are installed. For sake of discussion, lets just say that the batch is 100 pieces. These 100 lamps are tortured in various ways. They are turned on and off repeatedly. The voltage and current are turned up high and down low. The temperature and humidity are fluctuated to extremes. And then the lamps start dying. One by one. The torture continues until HALF of the batch (called B50) are dead. When the 50th lamp dies, the clock is stopped....and it reads 24,000 hours. This is the number that is published in the catalog and on the box. Trust me, it's waaaaaay more technical than that, but that's the gist of it.
Something to remember before we continue. If the 100 lamps above were in your shop, after 24,000 hours HALF of them are 100% dead. This would be bad, right?
LED lamps are tested the same way, in the same lab, with the same torture. But there's a problem. LED's dont die until long after they have dimmed out so much that they are useless. So, if you were told that they lasted 100,000 hours but after 50,000 hours they were so dim that you couldn't see anything, you'd be pissed, right?
The lighting industry drew a line in the sand at the point where a lamp is not doing it's job. It's at 70% of full light output, or " 70% of initial lumens" or L70. Once a lamp dims down 30%, it is considered no longer useful and essentially dead. Now, you might not think it's dead. In fact, you might think it's still pretty bright. That's cool. But...lets go back to that laboratory.
Let's put a batch of 100 LED lamps in the torture chamber and start the clock. When 50% of those lamps (B50) dim down to 70% of their initial lumens (L70), the clock is stopped. That's the number that is put on the box and in the catalog.
Can you spot the big difference between the 100 fluorescent lamps in the first test batch we did and the 100 LED lamps in the second test batch? In the LED batch, 100% of the lights are STILL BURNING. None of them are dead. In the first batch 50% of them are completely dark.
This is the huge difference that proponents of fluorescent lighting continually forget to tell you!
So, finally, let's compare a few real world items....
F32T8 generic lamp: 24,000 hours (B50)
LED retrofit tubes: 50,000 hours (B50/L70)
100w light bulb: 750 hours (B50)
LED equivalent to 100w light bulb: 20,000 hours (B50/L70)
26w CFL: 10,000 hours (B50)
As I stated above, the testing is far more technical and scientific than the way I explained it, but you get the idea.
I hope this helps you all understand the lingo a little better. Feel free to ask if there are more in-depth issues you would like to know about.
CD
One thing that you will often see compared is the life ratings of various lighting products. Average Rated Life numbers get thrown around alot in conversation but I bet that most people outside the lighting industry dont really understand what those numbers mean.
This is my attempt to explain it to the members of GJ, using plain english.
When a manufacturer states that a lamp's life is "X" hours, what does that mean? Does it mean that when the lamp gets used that many hours it will die? How do they know this? How is it possible for an LED manufacturer to know that his lamp will last 50,000 hours when it was only invented last week?
Let's look at a typical F32T8 lamp, which is commonly discussed on this forum. The run-of-the-mill T8 lamp has an Average Rated Life of 24,000 hours. The life testing is done in a laboratory environment. A sample batch of the lamps are installed. For sake of discussion, lets just say that the batch is 100 pieces. These 100 lamps are tortured in various ways. They are turned on and off repeatedly. The voltage and current are turned up high and down low. The temperature and humidity are fluctuated to extremes. And then the lamps start dying. One by one. The torture continues until HALF of the batch (called B50) are dead. When the 50th lamp dies, the clock is stopped....and it reads 24,000 hours. This is the number that is published in the catalog and on the box. Trust me, it's waaaaaay more technical than that, but that's the gist of it.
Something to remember before we continue. If the 100 lamps above were in your shop, after 24,000 hours HALF of them are 100% dead. This would be bad, right?
LED lamps are tested the same way, in the same lab, with the same torture. But there's a problem. LED's dont die until long after they have dimmed out so much that they are useless. So, if you were told that they lasted 100,000 hours but after 50,000 hours they were so dim that you couldn't see anything, you'd be pissed, right?
The lighting industry drew a line in the sand at the point where a lamp is not doing it's job. It's at 70% of full light output, or " 70% of initial lumens" or L70. Once a lamp dims down 30%, it is considered no longer useful and essentially dead. Now, you might not think it's dead. In fact, you might think it's still pretty bright. That's cool. But...lets go back to that laboratory.
Let's put a batch of 100 LED lamps in the torture chamber and start the clock. When 50% of those lamps (B50) dim down to 70% of their initial lumens (L70), the clock is stopped. That's the number that is put on the box and in the catalog.
Can you spot the big difference between the 100 fluorescent lamps in the first test batch we did and the 100 LED lamps in the second test batch? In the LED batch, 100% of the lights are STILL BURNING. None of them are dead. In the first batch 50% of them are completely dark.
This is the huge difference that proponents of fluorescent lighting continually forget to tell you!
So, finally, let's compare a few real world items....
F32T8 generic lamp: 24,000 hours (B50)
LED retrofit tubes: 50,000 hours (B50/L70)
100w light bulb: 750 hours (B50)
LED equivalent to 100w light bulb: 20,000 hours (B50/L70)
26w CFL: 10,000 hours (B50)
As I stated above, the testing is far more technical and scientific than the way I explained it, but you get the idea.
I hope this helps you all understand the lingo a little better. Feel free to ask if there are more in-depth issues you would like to know about.
CD