According to Cree, the XM-L2 boasts higher efficiency and more bang for your buck than the XM-L. So if you were to run two identical flashlights at, say, 800 lumens, with the only difference being the emitters, would the XM-L2:
- Be driven less?
- Produce less heat?
Have a better run time?
It’s so easy to just go with whichever one is newer, but I’d like to know what the real world results have to say.
Here’s some data on the Cree website, but I want to know what you all have found from testing and usage.
XM-L:
Maximum drive current (A) 3
Maximum power (W) 10
Light output Up to 1040 lm @ 10 W
Typical forward voltage (V) 3.1
XM-L2:
Maximum drive current (A) 3
Maximum power (W) 10
Light output Up to 1052 lm @ 10 W, 85°C
Typical forward voltage (V) 2.85
I think they are driven at the same input, but it comes down to LED efficiency. The XM-L2 is more efficient and provides more light output while being driven at the same input amperage.
I know the numbers tell one story, but my eyes don’t always follow suit.
I’ve also bought into the ‘newer must be better’ philosophy - but when I compare them side by side I see little if any difference. That applies to XM-L / XM-L2 and XP-G / XP-G2 as well.
I have two identical FourSevens Mini AA2s. One is XP-G2, but because it has a less perfect pattern, it is actually less effective than the earlier XP-G. Side by side, you’d swear the XP-G version is ‘brighter’.
You’ll see more improvement by fine tuning the emitter to the reflector, for example, than you will by upgrading the emitter. I get much greater satisfaction by finding a tint I like.
I’ll continue to buy –2 versions of course, but my point is don’t feel ‘under gunned’ just because you’re one generation back. The difference is NOT very visible, if at all. In my opinion, it’s not worth the money to upgrade a series 1 (for lack of a better term) emitter.
The difference in Cree gen1 and gen2 is more about efficiency, not about more lumens. More lumens happens, but it's not really visible to many eyes. It's just like the new car or new ipad. It's a status symbol mostly and it's unfortunate as the gen1 leds are now cheap and work fine for modding. I just got rid of all my gen1 XM-L only because no one wants XM-L any more, not because I am enamored with XM-L2 in any way.
So if I take the scenario I initially posted (both driven to produce 800 lumens), the slightly more efficient XM-L2 should produce the same amount of lumens while producing less heat, and requiring less current… right? I guess that’s more of my question.
Maybe my scenario would have to change a little… If both were identical except the emitter and the driver so that the driver would top out at driving both emitters at 800 lumens… would the XM-L2 produce less heat and require less current?
The big issue that has come out about the XM-L2 is that it (supposedly) requires higher vF (forward voltage). This means your battery will likely sag earlier reducing current output since the XM-L2 is trying to pull more voltage than the cell can deliver. So now your reducing output approximately to that of the XM-L. Like Comfy has posted before, I think it really comes out in the wash comparing an XM-L to an XM-L2 on a typical 18650.
@ the OP, keep in mind those specs are at 25ºC for XM-L and at 85ºC for XM-L2, if you correct the XM-L for 85ºC you will see the difference in the spec sheets.
IN the XM-L sheet you will see a chart for output vs die temperature, use that for correction caluclations
What you’ve heard so far is correct. I’ll just give you the practical low-down on this subject as I’ve had a number of lights I’ve played with to compare the two…
Comparing stock budget light to stock budget light, one with XM-L and the other with XM-L2, you will typically not see any brightness advantage at all. This is due to A) samples varying in quality and not being fully or equally driven, and B) differences in tint (usually yellower for XM-L2), making the second gens seem warmer, and therefore, less bright. But comparing higher-end lights to each other (with XM-L vs XM-L2), you will see some noted advantages with XM-L2.
Comparing modded lights to stock lights (either XM-L or XM-L2): There is no comparison! The second gens have the capacity to be driven much harder and effectively up in high current ranges, whereas the XM-L was “done playing” at 4.2 amps. In these ranges, the new babies totally rock out.
With regard to single-cell lights, that pesky forward voltage requirement of XM-L2 does seem to work against things, but with regulated drivers, this isn’t a problem. This is another reason I’ve come to dislike DD lights.
So, in conclusion, if you’re ever questioning re-buying your old XM-L favs with XM-L2, I’d say it’s not worth it.