Fenix with LuxIII ??

What do you think the result would be if I were to drop a TWOH LuxIII straight into a Fenix L1P (Ver2.5).

Would the underdriven LuxIII give more lumens / efficiency than the LuxI - driven at spec?

Just a thought....
Any of you LED Guru's care to to comment.


Tim

I wouldn't classify myself as an LED guru, but the datasheets from Lumileds imply you might not be much better off. For the sake of simplicity, let's assume that the Fenix drives the emitter at its claimed current of 350mA.

Here's the datasheet for the LuxIII (pdf file):

http://www.lumileds.com/pdfs/DS45.PDF

Figure 6 at the top of page 12 indicates that the normalized luminous flux at 350mA is going to be about 60% of the flux at the specified current of 700mA.

Table 1 on the top of page 3 indicates that the typical luminous flux at 700mA is 65 lumens for a white emitter.

So you can guesstimate about 65 x 0.6 = 39 lumens.

Note that Lumileds cautions: "Driving these high power devices at currents less than the test conditions may produce unpredictable results and may be subject to variation in performance. Pulse width modulation (PWM) is recommended for dimming effects."

The datasheet for the LuxI (pdf file):

http://www.lumileds.com/pdfs/DS25.PDF

Table 1 at the top of page 4 indicates that the typical luminous flux for a white LuxI driven at 350mA should be 45 lumens.

Of course, YMMV. The figures quoted above assume that the LuxIII's Vf at 700mA is 3.7V (which would classify it as a K bin), and the LuxI's Vf at 350mA is 3.42V (J bin). So if your Fenix happens to have a LuxI with a high Vf (R3J or R3K), you might see some improvement after transplanting your TWOH.

You also might want to keep an eye on this thread, containing pbarette's experiments with a Fenix circuit with a R/O Lux3 (of unknown bin) and a QYAJ Lux 1:

http://candlepowerforums.com/vb/showthread.php?t=99516

Tests in general have shown LED efficiency increases at lower currents, but the color balance can change. So a led that's very neutral at 700 mA can get a color cast at 350 mA.

i recommend at least two bins difference

so if you already have a R bin(today typical) than a T bin Lux1(<--one) makes sense. ;-)

It's not that easy. The T bin is a 3 watt part and the R bin is a 1 watt part. That is, to get the T output level you have to drive the T part at 900 mA or something like that, instead of 350 mA (the Lux3 Vf tends to be a little higher too). The question is whether a T-bin Lux3 underdriven to 1 watt will make more output than the R-bin Lux1. The answer is: probably not, at least not noticably.

It might be possible to crank up the power a bit more, but then you really can't run on alkalines any more, and you lose one of the Fenix's big attractions.

I think you basically have to wait for the next generation of more efficient leds, to get much improvement. If anything, they should back the power off a little, for better regulation with alkalines.

Thanks for the response guys,

Seems to me that there's no point spoiling a perfectly good Fenix for the sake of a few lumens and definately not worth turning it into a 'greenie' in the process.

If it aint broke - Dont try to fix it.

Tim.

Of course, there are a few S-bin Lux Is that should be a nice improvement but they don't often show up to market and I think the last ones were as much as a cheap Lux V - $28 plus shipping!