5mm vs Cree

Which is more efficient between a 5mm LED and "normal" cree style LED like an xpg2 at lower outputs say 10 lumens or less??

For practical purposes, I'd expect the driver to make the biggest difference.

In general, LED's are more efficient when underdriven and when kept at lower temperatures. The larger emitter size of most surface mount LED's like the XP-G2, and the better thermal path both suggest that all else being equal, the surface mount LED would be more efficient.

It's hard to find direct comparisons, because not many 5mm LED have lumen output published, and I don't know how to find out if the emitter is reasonably comparable to the surface mount types that more information is available for. Comparing two of the most equivalent I could find specs for with similar CCT and CRI seems to show opposite the expected effect, I suspect more because the die and phosphors are different than that I misunderstand the general principles.

Yuji BC 5600K 93 CRI: 7.3 Lumens / 20mA * 2.9 V = 126 lm/W
Nichia 219B ~5300K 93 CRI: 111 Lumens / 350ma * 2.96 = 107 lm/W

I'm not sure how that Nichia performs at 20mA - the derating graph in the datasheet is too small to read accurately. Sketching some lines on the graph in MS Paint, I think at 20mA it's about 6% of the 350mA brightness. Also, the forward voltage is lower at 20 mA, probably about 2.7 V. In that case:

Nichia 219B ~5300K, 93 CRI: 111 lumens * 0.06 / 20mA *2.7V = 124 lm/W

Inova x5 (5 5mm's) says 30 lumens 18 hours
Fenix pd35 (1 xml2) says 50 lumens 38 hours on 18650 so id roughly half the runtime for cr123 comparison with inova. Newer led still wins.
I looked a selection of lights out of interest, similar looking results.

I think iamlucky has it, the driver is the wild card. His rough calculation shows the LED's are about equal. (all hail the mighty 5mm!)

You can't just cut an 18650 time in half to approximate two CR123's, BTW. The 18650 is 4.2 Volts, the 123's are 6 volts, you need to look at total power capacity, not just mAh's. That would give even more advantage to the Fenix example above, and it is running about twice as bright (assuming you buy manufacturer's specs). That would only tell me that Fenix drivers are very efficient, but I already knew that. The Inova X5, at least my old ones, I think only uses resistors to throttle the 6 Volt source running the 5 LED's. Would not expect that to be very efficient, as it is just dumping excess power as heat off of the resistors.

I'm a simpleton. Soooo basically if they used the same driver at the same output they'd be equally efficient or close?

Yuppers (because Yup is too short for CPF)

LOL. That's pretty cool in my opinion. Mighty 5mm indeed.

Hondo said:

Yuppers (because Yup is too short for CPF)

Click to expand...

That is awesome if its close, I know my calculations were rough that was the point really, the new dual mode x5 must be more efficient.
The fenix is quite a bit brighter too, I'm with the newer leds .
So whos going to build and test this for sure ?

I keep thinking of an E01 where you twist on to sub lumen output and keep twisting to fully tightened for full output of 10. That would make me happy.......and fulfilled.....with a heart full of love.

gurdygurds said:

I keep thinking of an E01 where you twist on to sub lumen output and keep twisting to fully tightened for full output of 10. That would make me happy.......and fulfilled.....with a heart full of love.

Click to expand...

Try dropping a square of QTC material into an e01.

Jabe I was just reading a thread about folks trying that out. The pictures don't show anymore and one guy said he stacked some QTC and then just set it on top of the battery and screwed on the head. If you drop it in the tube does that take the place of the spring? Have you tried it and if yes how does it compare to a QTC Eiger?

jabe1 said:

Try dropping a square of QTC material into an e01.

Click to expand...

I did not think QTC could work with a spring. Never reach enough force to full output. Maybe with additional material to cause the spring to fully collapse?

You need to use a host with no spring - a so-called "battery-crusher" type flashlight

Matterhorn should work ... ?

qtc wont work with a e01, but it works fine with a arc aaa.
The "5mm lights" will usually run the volage on the battery down a lot further than any light with a xp-g. So when i take out dead batteries from a normal aaa light with a xp-g, it will still work for hours and hours (or days) in a 5mm aaa light.

After quickly reading this thread I'd like to add one point. The Vf (forward voltage) of each diode (light emitting diode) will play a part in efficiency.

Some red emitters have rather low Vf, if you are looking to optimize efficiency

I'm no electronics whiz, but doesn't the QTC itself reduce the efficiency of the total circuit?

So if you want variable output, at QTC is good.

But if you're looking for maximum efficiency (i.e. hours at a given output), a QTC is bad.

I think you're right. It is a variable resistance, so it would be like just using a resistor to lower output, and dumping power out of the resistor as heat.

I'm not an expert, but it's much more efficient than a resistor. I think the quantum effects largely avoid the heat losses ....

The wiki entry notes that classical electrical resistance is linear while quantum tunnelling is exponential.

Hmm... Sounds cool, too bad it needs a battery crusher style light to function.