--Originally posted on the "Type of led" thread in the DIY forum by me, but I liked the writeup.--
The term "lm/w" stands for "lumens per watt".
Please point out the math errors I no doubt made.
Comparing the Cree XM-L and Luxeon M
The Luxeon M neutral white (higher bin, 70 CRI) has a test efficiency(700ma) of 125lm/w, with a typical luminosity of 980lm/w. The XM-L test efficiency is 127lm/w (700ma), with a typical luminosity of 260 lm/w for the 3700k-5000k higher bin.
However, the XM-L tests are done with a temperature of 25*C juction temperature, versus the test junction temperature of Luxeon M at 85*C. If we compensate for that (XM-L datasheet has a graph) then it really only achieves about 229lm for an efficiency of 106 lm/w, or 88% of what it is rated for at 25*C. That's only 89% as efficient as a single Luxeon M die.
But one might argue that the XM-L can be run at higher currents, to push out more lumens. However, at a current of 2000ma, almost three times the current used in the above calculations, it can be seen that it only puts out 2.4x more light for a total luminosity of 643lm, or an efficiency of 100lm/w. And compensating for temperature again, we see that it is really only about 566lm, and 89lm/w. About 71% as efficient as a Luxeon M, or 83% as efficient as its 700ma test current.
Cost specs:
At Led Group Buy, a standard XM-L neutral white costs $8, and at Steve's Leds, a Luxeon M costs $12. Both are mounted to PCBs.
At 700ma test current, it takes 4.27(980lm/229lm) XM-L leds to match one Luxeon M, or $34. At 2000ma, 1.76(980/ 556) are needed, or $14. I guess if you ran them at 3000ma, you could almost match a Luxeon M with a single die, but then your efficiency would be down the meephole.
Following this post will compare Luxeon M to XM-L2 leds. The difference is not so staggering there, but give me a few minutes.
XM-L datasheet: http://www.cree.com/....g/XLampXML.pdf
Luxeon M datasheet:
www.philipslumileds.com/uploads/354/DS103-pdf
Comparing the Cree XM-L2 and Luxeon M
A Luxeon M from Steve's Leds, mounted to a PCB, costs about $12. A XM-L2 from Led Group Buy, mounted to a PCB, costs about $9. Please tell me if you find a cheaper source, and I will be happy to recalculate.
Let's a take a look at the numbers.
Unlike the previous comparison, both leds were (mercifully) tested for at a junction temperature of 85*C. So there will be no adjustment needed.
Looking at the 700ma test current on Luxeon M leds, we find they put out 980lm typically, for the 70CRI 4000k bin. That's 125lm/w efficiency.
The 700ma test current on XM-L2 leds, for the T5 bin (3700-5000k), we get 260lm. That's 130.2 lm/w. That's 4% more efficiency than a Luxeon M.
At 1000ma test currents, for the same bins:
Luxeon M: 1323lm, for 118lm/w.
XM-L2: 357lm, for 123lm/w. Still about 4% higher than the Luxeon M.
The Luxeon M costs about 33% more than a XM-L2. It puts out, at a test current of 700ma, 980lm. The XM-L2 puts out 260lm at the same test current that it's rated for.
980/ 260 = 3.77. You need 3.7 XM-L to get the same output of a single Luxeon M.
$9 x 3.7 = $33. A single Luxeon M is $12.
Maybe it's just me, but that 4% higher efficiency just doesn't seem worth the 2.5x increase in cost. I can work out the savings math if anybody wants, depending on the cost per kW in your area.
XM-L2 datasheet:
http://www.cree.com/~/media/Files/Cr...ML2.pdf
Luxeon M datasheet:
www.philipslumileds.com/uploads/354/DS103-pdf
The term "lm/w" stands for "lumens per watt".
Please point out the math errors I no doubt made.
Comparing the Cree XM-L and Luxeon M
The Luxeon M neutral white (higher bin, 70 CRI) has a test efficiency(700ma) of 125lm/w, with a typical luminosity of 980lm/w. The XM-L test efficiency is 127lm/w (700ma), with a typical luminosity of 260 lm/w for the 3700k-5000k higher bin.
However, the XM-L tests are done with a temperature of 25*C juction temperature, versus the test junction temperature of Luxeon M at 85*C. If we compensate for that (XM-L datasheet has a graph) then it really only achieves about 229lm for an efficiency of 106 lm/w, or 88% of what it is rated for at 25*C. That's only 89% as efficient as a single Luxeon M die.
But one might argue that the XM-L can be run at higher currents, to push out more lumens. However, at a current of 2000ma, almost three times the current used in the above calculations, it can be seen that it only puts out 2.4x more light for a total luminosity of 643lm, or an efficiency of 100lm/w. And compensating for temperature again, we see that it is really only about 566lm, and 89lm/w. About 71% as efficient as a Luxeon M, or 83% as efficient as its 700ma test current.
Cost specs:
At Led Group Buy, a standard XM-L neutral white costs $8, and at Steve's Leds, a Luxeon M costs $12. Both are mounted to PCBs.
At 700ma test current, it takes 4.27(980lm/229lm) XM-L leds to match one Luxeon M, or $34. At 2000ma, 1.76(980/ 556) are needed, or $14. I guess if you ran them at 3000ma, you could almost match a Luxeon M with a single die, but then your efficiency would be down the meephole.
Following this post will compare Luxeon M to XM-L2 leds. The difference is not so staggering there, but give me a few minutes.
XM-L datasheet: http://www.cree.com/....g/XLampXML.pdf
Luxeon M datasheet:
www.philipslumileds.com/uploads/354/DS103-pdf
Comparing the Cree XM-L2 and Luxeon M
A Luxeon M from Steve's Leds, mounted to a PCB, costs about $12. A XM-L2 from Led Group Buy, mounted to a PCB, costs about $9. Please tell me if you find a cheaper source, and I will be happy to recalculate.
Let's a take a look at the numbers.
Unlike the previous comparison, both leds were (mercifully) tested for at a junction temperature of 85*C. So there will be no adjustment needed.
Looking at the 700ma test current on Luxeon M leds, we find they put out 980lm typically, for the 70CRI 4000k bin. That's 125lm/w efficiency.
The 700ma test current on XM-L2 leds, for the T5 bin (3700-5000k), we get 260lm. That's 130.2 lm/w. That's 4% more efficiency than a Luxeon M.
At 1000ma test currents, for the same bins:
Luxeon M: 1323lm, for 118lm/w.
XM-L2: 357lm, for 123lm/w. Still about 4% higher than the Luxeon M.
The Luxeon M costs about 33% more than a XM-L2. It puts out, at a test current of 700ma, 980lm. The XM-L2 puts out 260lm at the same test current that it's rated for.
980/ 260 = 3.77. You need 3.7 XM-L to get the same output of a single Luxeon M.
$9 x 3.7 = $33. A single Luxeon M is $12.
Maybe it's just me, but that 4% higher efficiency just doesn't seem worth the 2.5x increase in cost. I can work out the savings math if anybody wants, depending on the cost per kW in your area.
XM-L2 datasheet:
http://www.cree.com/~/media/Files/Cr...ML2.pdf
Luxeon M datasheet:
www.philipslumileds.com/uploads/354/DS103-pdf
