# Best Red LED of 2011?



## Chrontius (Apr 6, 2011)

I'm looking to build a bike taillight. What's the best red LED available? XM-L? MC-E? Throw is not an issue, there will be a diffuser.


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## Harold_B (Apr 7, 2011)

You can narrow it down by at least one since the XM-L isn't available in anything but white.


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## Chrontius (Apr 7, 2011)

Cree's only relevant product is the XP-E.

i think that luminous makes some SST-series in red, and I think there's a red Dragon-series by Osram...

Maybe Nailbender's the guy to ask?


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## JohnR66 (Apr 7, 2011)

Six Cree 5mm reds driven at 40ma will be plenty bright for a tail light and is less of a power issue.


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## LEDAdd1ct (Apr 7, 2011)

I would say your best bet is here and here.

Good luck!


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## bshanahan14rulz (Apr 7, 2011)

What ever happened to the "superflux" package?


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## PCC (Apr 7, 2011)

For a while I had envisioned using a red SST-90 driven at 3A for a bike tail light, but, I've been told that this would be stupid bright and that you would blind everyone behind you with it. You'd actually risk being run over because the driver was blinded by the very light that is supposed to keep you safe.


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## blasterman (Apr 7, 2011)

Just get a regular Cree or Rebel 3watt Red and under-drive it at 100mA or so. That's plenty bright, and you hardly need to worry about heat-sinking.


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## znomit (Apr 7, 2011)

blasterman said:


> Just get a regular Cree or Rebel 3watt Red and under-drive it at 100mA or so. That's plenty bright, and you hardly need to worry about heat-sinking.


 
+1
Note reds haven't increased in efficiency like the whites have so don't be too fussed about getting the latest.


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## dellayao (Apr 18, 2011)

i love cree XM-L,but it is a little expensive.


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## Oznog (Apr 18, 2011)

znomit said:


> +1
> Note reds haven't increased in efficiency like the whites have so don't be too fussed about getting the latest.



Not true! Luxeon Rebels shot up QUITE a bit recently, the Vf is notably lower, and the thermal resistance is down a lot. So the efficiency and possible power is quite improved.

However, for a taillight, you gotta consider how it might blind people. The diffusing pyramids of a common red cover won't help as much as you think if the emitter is not far underneath it. If the emitter's not far underneath it, what you still get is one blindingly bright spot on the red lens and the rest of the lens is still dark because no light hits it.

This is not as big a problem if the light is deep, and there's enough room for the lambertian distribution to cover the whole lens, making an even glow. But a bike light probably won't have that much space. This is where many smaller, lower-power devices do have some benefit, as they can more evenly distribute a glow even if they're not far behind the lens.


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## purduephotog (Apr 18, 2011)

At what wavelength?

Red Rebels are 2$ at 630nm, red ledengins are 660nm and 10$, and red avagos are 630-645nm at 2$.


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## jeffosborne (Apr 19, 2011)

I would choose the red-orange at 617nm, $3.03 each at Future Electronics:

http://www.futureelectronics.com/en...ters/colour/Pages/8109118-LXML-PH01-0050.aspx

In other threads, the red-orange has been mentioned as the color of choice for auto tail lights. 50 lumens per watt for the part listed above. The red Rebel's are available up to 40 lumens per watt only.

Jeff O.


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## bshanahan14rulz (Apr 19, 2011)

Yes, I agree, shorter wavelength reds are more visible.


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## shao.fu.tzer (Apr 19, 2011)

Funny, I thought I replied here last night - check out:

Osram
*LR CPDP*


OSLON SSL 150, red (620 - 632 nm)

132lm @ 1A with a 150 degree viewing angle...


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## blasterman (Apr 19, 2011)

IMHO, 625-630nm *is* red-orange.

If really orange is preferred along with blinding tail gaters in daylight, how about 400 lumens of 612nm from a triple rebel star?

http://www.luxeonstar.com/Red-Orange-617-nm-20mm-Tri-Star-Rebel-402-lm-p/mr-h2070-20t.htm


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## Oznog (Apr 19, 2011)

purduephotog said:


> At what wavelength?
> 
> Red Rebels are 2$ at 630nm, red ledengins are 660nm and 10$, and red avagos are 630-645nm at 2$.


 
Both the red and the red-orange jumped in technology. Contrast the LXML-PDxx (red)/LXML-PHxx (red-orange) with the "LXM2-xxxx" parts. It's a different technology, rather than a simple quality increase that could simply be specified by different binning.

Whatever that tech change is, it's across the industry. Red & red-orange all went from ~2.5v-2.9v Vf to ~1.9v-2.2v Vf and as a whole, the efficiency jumped across the board for everyone. EXCEPT ledEngin, though. They're still selling only high-Vf red/deep red and they're sort of obsolete.

The older 2.5v-2.9v Vf devices are still around, but generally undesirable. Even for an apparently less "critical" design like a bike light, the battery consumption, cooling issues, and simple power-per-device makes the older ones less cost-effective, even though they appear cheaper at first.

Yes the red-orange is more "visible" and generally better for a bike light. The pure red is a bit more visually striking, but fewer lumens.
Red-orange is actually pretty much the same as red in terms of mW of light energy out per W of energy in, and these devices with a red-orange and red in the same package generally have identical mW of light energy outputs. The lumen scale is biased by wavelength to compensate for the human eye bias, and the slope's pretty steep in the reddish end, 100mW of 625 nm red light energy scores notably lower lumens than 100mW of 615nm red-orange light energy.

But, since visually perceived lumens are the end goal, the red-orange wavelength wins.


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## bshanahan14rulz (Apr 19, 2011)

Looks like this push for more efficient red-orange vs. red came mostly from the automotive industry.


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## blasterman (Apr 19, 2011)

> But, since visually perceived lumens are the end goal


 
We have some new LED street lights using the red-orange emitters, and are likely around 615nm. They are visually confusing, and not nearly as attention grabbing as more typical ~630nm emitters or lenses.

660nm technology really takes a hit brightness wise in terms of photopic sensitivity over more common 630, but IMHO we shouldn't be going shorter than ~630nm for traffic use.


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## jeffosborne (Apr 19, 2011)

Holy crap Oznog, you were right! Thanks for the heads up. 70 lumen per watt red-orange Rebel, $3.58:

http://www.futureelectronics.com/en...ters/colour/Pages/5001765-LXM2-PH01-0070.aspx

134 lumens at 700ma, not bad!

Jeff O.


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## Neondiod (Apr 20, 2011)

Better still, it's 72 lumens (typ) at 350 mA x 2,1 V equals 98 lm/watt. Or 95 lm/watt min.

Hey jeffosborne, you draw shame over your avatar


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## blasterman (Apr 20, 2011)

If 615nm is the new 'red-orange' then it's only a matter of time before cyan becomes the new green.


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## VegasF6 (Apr 20, 2011)

see below


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## VegasF6 (Apr 20, 2011)

blasterman said:


> We have some new LED street lights using the red-orange emitters, and are likely around 615nm. They are visually confusing, and not nearly as attention grabbing as more typical ~630nm emitters or lenses.
> 
> 660nm technology really takes a hit brightness wise in terms of photopic sensitivity over more common 630, but IMHO we shouldn't be going shorter than ~630nm for traffic use.


You confused me here for a moment, then I realized you meant LED traffic signals instead of street lights.


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## purduephotog (Apr 21, 2011)

Oznog said:


> Both the red and the red-orange jumped in technology. Contrast the LXML-PDxx (red)/LXML-PHxx (red-orange) with the "LXM2-xxxx" parts. It's a different technology, rather than a simple quality increase that could simply be specified by different binning.
> 
> Whatever that tech change is, it's across the industry. Red & red-orange all went from ~2.5v-2.9v Vf to ~1.9v-2.2v Vf and as a whole, the efficiency jumped across the board for everyone. EXCEPT ledEngin, though. They're still selling only high-Vf red/deep red and they're sort of obsolete.
> 
> The older 2.5v-2.9v Vf devices are still around, but generally undesirable. Even for an apparently less "critical" design like a bike light, the battery consumption, cooling issues, and simple power-per-device makes the older ones less cost-effective, even though they appear cheaper at first.


 (snip)

LedEngin is selling their parts for folks that WANT 'real' red... and for those building targeted grow lamps.

I don't like 630nm reds. I do like 660nm reds. *shrug* The HVS (Human Visual System) is unique to each individual.


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