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- Thread starter Jsub
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People seem to think that they will get a better result using them over an earlier XM-L led.

If you check the numbers, they actually put out less light.

So why this LED?

For thermal reasons as far as I understand it. This LED produces less heat so you can use smaller heatsinks for the same output.

Since we typically have enough cooling in a well designed dive light, I don't see the point of paying more for this new led when you can get the same result with a cheaper led.

this is just what I think about it, others may disagree

regards,

Johan

I disagree. The XM-L data sheet specifies luminous flux values at 25C, while the XM-L2 is specified at 85C. That's a big difference.

The cool white U2 bin XM-L has minimum 300 lm at 700mA, calculated 742 lm at 2000mA, 25C.

The cool white U2 bin XM-L2 has minimum 300 lm at 700 mA, calculated 728 lm at 2000mA, 85C.

To compare apples to apples though, you have to use the XM-L2's calculated output at 700mA, 25C. That's 340 lm.

So the XM-L2 is actually substantially brighter UNDER THE SAME CONDITIONS, compared to the XM-L.

As for thermal reasons, they are minimal. The thermal resistance of the package is identical (2.5C/W). The forward voltage spec is a tiny bit lower, but that's probably entirely due to it being specified at 85C instead of 25C.

You do get more light at the same power input, so that means a little less heat. We don't have numbers to calculate accurately, but we can do a little better than a WAG. If the XM-L is 25% efficient at 10W, which seems like a reasonable estimate given numbers I've seen here and there, then the XM-L2 might be 340/300 times 25%, or 28% efficient. So the heat generated would be 7.2W instead of 7.5W. Keep in mind I put together numbers that don't belong together in order to get this estimate, so it's not to be counted on. However, it should be in the ballpark.

The cool white U2 bin XM-L has minimum 300 lm at 700mA, calculated 742 lm at 2000mA, 25C.

The cool white U2 bin XM-L2 has minimum 300 lm at 700 mA, calculated 728 lm at 2000mA, 85C.

To compare apples to apples though, you have to use the XM-L2's calculated output at 700mA, 25C. That's 340 lm.

So the XM-L2 is actually substantially brighter UNDER THE SAME CONDITIONS, compared to the XM-L.

As for thermal reasons, they are minimal. The thermal resistance of the package is identical (2.5C/W). The forward voltage spec is a tiny bit lower, but that's probably entirely due to it being specified at 85C instead of 25C.

You do get more light at the same power input, so that means a little less heat. We don't have numbers to calculate accurately, but we can do a little better than a WAG. If the XM-L is 25% efficient at 10W, which seems like a reasonable estimate given numbers I've seen here and there, then the XM-L2 might be 340/300 times 25%, or 28% efficient. So the heat generated would be 7.2W instead of 7.5W. Keep in mind I put together numbers that don't belong together in order to get this estimate, so it's not to be counted on. However, it should be in the ballpark.

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What is the equivalent of a T6 tint for the XM-L2?

Tint, AKA chromaticity, would be the next suffix, a number from 0 to 8 and a letter from A to D. Low numbers are cool, high are warm.

All XM family parts use the same binning codes, so an XM-L-T6-1C would be the same brightness and color as an XM-L2-T6-1C. However, I suspect gen2 parts will start at U2 flux bin, so you probably won't find a T6.

Yeah cheers your explanation was like a revelation of understanding to me

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All XM family parts use the same binning codes, so an XM-L-T6-1C would be the same brightness and color as an XM-L2-T6-1C. However, I suspect gen2 parts will start at U2 flux bin, so you probably won't find a T6.

No. The XM-L is binned based on it's physical temperature being 25C or 77F. The XM-L2 is binned at 85C or 185F. An XM-L2 Led running at 25C would be about 11-12% brighter than it's rated(T6 for example) An XM-L running at 85C is about 11-12% dimmer than it's rated(based on 700mA current) These numbers may vary with current differences.