Yes, these low voltage leds loose a lot of their efficiency in our use in flashlights because the difference between led voltage and battery voltage is higher, while the two most used types of drivers, lineair and direct drive (both are simple and compact), are pretty bad handling that: the lineair driver just burns off the voltage difference and the direct driver results in a very high current region in which the led is least efficient. Small batteries are limited in current so in direct drive the led is still in a quite efficient region, but then the battery works against efficiency: at their highest current the capacity of the battery decreases.
Perhaps the voltage of the Luxeon V is so low that the difference between battery and led voltage is high enough to use a buck driver? (I have no idea, not into driver electronics). Say you want 3A (a bit over 1000lm OTF), the led voltage is then 3.2V, the battery voltage under 3A load is for most of the drainage over 3.6V. Hmm, 0.4V difference is probably not enough. For 1A/450lmOTF it may work.
Jerommel is right. The losses in thick lines at low voltage is the same as in thin lines at high voltage. That’s why the E-backbone of Netherland is running on 380 kV. To “save” on the cost of lines, which are of aluminum with a steel core. And the cost of electricity pylons, which have to carry less weight. Insulators are more expensive at ultra-high voltage.
I might remember it wrong but I thought I have red that 0.4 volt difference will be enough for some buck regulator’s.
Could also have been for a different type driver…
A buck driver is always possible, but doesn’t always make sense. Most stock single-cell lights with 3V LED (XM-L2 for exmaple) have a buck driver. A lower VF means that the output stays constant for higher percentage of the runtime and the average current pulled from the battery is lower. So the lower the Vf, the more sense a buck driver makes.
why use this led in 1000 lumen light, i mean, if you want 1000 lumen, go with xpl-hi,hd, xm-l2, or even xp-g3, and it’s also easier to reflow the led on MCPCB
if i use this led, i will push it over 1800, close to 2000 lumen(or even higher)
LEDs are more efficient when they are driven softly (look at the slope of the graph in the OP). So to acheive 1000Lm, a “2000Lm” LED driven at 50% will be more efficient than a 1000Lm LED driven at 100%.
Djozz, ylu know this was bound to come…please do the Q8 with these?
For me newbie it is kind of mixed.
On the one hand lots of lumens, on the other driver burning off volts. (And end Ferry Mingele mode )
If these are a good Q8 candidate, we really should have the XML pad ledboard redesigned to have pads for this as well.
XML and XHP70 would not fit, but these small pads would.
Hmm, ok, I will mod a Q8 with these, but I may wait for the new ones to do that. But mind that the stock light puts out 5000 lumen at 20A, and with Luxeon Z’s it is 8000 lumen at 36A, it will get kind of way too hot.
Thanks for the test djozz. Need to get you some samples of XP-L2. I’d donate to the cause. Impressive that the 4000k Luxeon V has almost identical output to a 6500k SST-40, and at a lower voltage to boot. Tint looks wonderful too! Can’t wait for some high CRI and more color temps.
How much does a custom run of DTP copper boards usually cost?
I just posted over on RMMs thread to see if he has any plans to stock the Luxeon V and perhaps even get some custom DTP boards made up for it. He has his MTN Quad boards which are top notch, so if he did a Luxeon V board I would be in for quite a few. A triple or quad Luxeon V board would be really interesting as well.