Luxeon Efficiency

Recently, I have been thinking about building lights for mountain biking, I'm sure there have been many threads raised here. I have been debating, do I use Halogen, Luxeon, or buy HID.

If I were to build, the debate is between a 20W MR16 Halogen and 3x3W Luxeon LED at 1A. The LuxeonIII run at 240 lumens, whereas the MR16 would run at 500 lumens. Each basically work out to having the same light output per Watt. I thought that LEDs were supposed to be better when it came to battery usage?

Is there something I'm missing? Is the only reason for me to opt for the Luxeons is the colour temp?

Thanks for any info

Welcome to cpf! /ubbthreads/images/graemlins/grin.gif
T5 conventional leds and high powered Luxeons dont change color much when the batteries start winding down.
There's just less of it.
The halogens change from incandescant white to a less than useful amber as the batteries lose power.
We have forums for many different light sources here for different folks with different strokes. /ubbthreads/images/graemlins/wink.gif

As for me, I like the leds for my line of work in security.
I cannot be having regular bulbs blowing and leaving me in the dark while I'm doing my foot patrols.
Well designed led lights can last you a lifetime without a single bulb change and would be good for any biker not wanting to pack a spare bulb.

White LEDs, with current technology, are not much more efficient than the best incandescent lights with the same brightness.

That being said, one should be careful in referring to "3W Luxeons," since strictly speaking there's no such thing. There is a Luxeon III, which consumes roughly 3 watts when driven at its specified current. It's a nominal value that is merely approximate--in the same way that a 2x4 wood beam does not really measure 2 inches by 4 inches. The actual power consumed by a Luxeon III depends upon its actual operating current (determined by the circuit) and its forward voltage (individually variable).

Disagree

The MR16 however is not typical of halogen lamps, whereas Luxeons are typical of LED's. Let me know where you can find a 10 watt halogen that produces 20 lumens per watt.
There aren't any. With incandescents and most lamps, luminous efficiency goes down with the wattage. 1 watt, 3 watt and 5 watt luxeons are all good for roughly 25 lumens per watt at realistic drive power. 1 3 and 5 watt incandescents, and even halogens cannot get anywhere near that figure. 10 lumens per watt in that category if you are lucky.

Having done runtime tests with my FT-3C (72 lumens at FULL POWER), I can say that LEDs appear to be a LOT more efficient as the batteries wear out. With dead batteries, LEDs can still give good light while an incandescent won't even turn on at all. My incandescents die very quickly once the batteries go into yellow (yellow meaning "marginal" on the battery tester). However, my FT-3C (3-watt LED) gives good to excellent output for about 16 hours, and I'm now up to about 46 hours and it is still giving useful light (enough light to navigate in a room, and more output than my fresh Arc AAA). This is with 2 DEAD batteries, and a third battery that is at the high "red" zone (red being "replace immediately"). I'm still running the test as I type this, and its still pumping out useful light and hasn't shown much signs of degrading over the last 8 hours. The closer the batteries are to dead, the slower they degrade on this LED it seems. 46 hours of useful light output IMO is exceptional from a 3C flashlight (I consider this light and the EL 3P to be ideal emergency lights due to the outstanding runtime). While its no longer bright enough for throw (long distance), its still giving plenty of light for close range navigation.

My understanding is that incandescents are the opposite--they are far more efficient with FRESH batteries.

I think you're right now that I've checked some numbers. Even a 100-watt household lamp (clear) provides only about 17 lumens/watt, which a Luxeon could easily beat. Still, the efficiency of white LEDs is not a huge advantage over what you can get from incandescents, particularly since the application in question involved light output in the hundreds of lumens. (This is assuming that optimal power is available--no weakening batteries, etc.)

I want to make sure that people aren't disappointed after hearing the misconception of "ten times more efficient" that is frequently tossed around.

I'm not sure the MR16 would really get 500 lumens. I think may 375 is more realistic. And in any case, even if it does, 10 lumens/watt or less is typical of low-wattage halogens. The average Luxeons these days seem to be getting 25 to 30 lm/W, and the best bins get 40+ lm/W. When your battery starts running down, LEDs actually get more efficient. At 350 mA a typical LIII might get 25% better efficiency than at 700 mA. Another thing working in favor of the LEDs is that the bluer light is actually about 1.5 to 2 times as good for seeing as the yellower incandescent light under typical nightime conditions. Or put another way, the scotopic lumens are higher than the phototopic lumens. This means a 25 lm/W LED actually produces the equivalent of over 40 lm/W during scotopic conditions.

Another big advantage LEDs have over incandescent and HID is shock resistance. For your intended application (mountain biking) this is very important. I can't say how many bulbs I had fail prematurely thanks to NYC's potholed streets, but it was enough that I gave up entirely on having lights on my bike until LEDs came along. The shock resistance combined with the long lifetime (6000 hours even for the 5mm LEDs that I use) mean that I no longer have to worry about my light failing in the middle of a ride. As long as the batteries are charged I'm OK. I'd say definitely go with the LEDs over the other two options. There is no contest between LEDs and incandescents for low power lighting applications. While HID may be more efficient, it is also more prone to shock damage, and much more expensive. And in a few years you'll be able to upgrade the LEDs in your light to more efficient ones which will likely approach or better current HID efficiency.

Thanks everyone, all of this makes good sense.