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Old 10-29-08, 07:36 AM   #1
cbr2702
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Homebrew LEDs vs IQ Fly, Supernova E3, etc

Lots of people have told me that LEDs are getting more efficient much faster than people can make commercial lights. They've also told me that commercial lights have optics optimized for biking that a DIY light couldn't match. So, what I'm wondering is, which is the dominant factor? Are the availible LEDs bright enough to compete with the IQ Fly, Supernova E3, etc even without the well focused optics?

Where would you expect a DIY led light to fall in a comparison like:
http://www.velociped.ch/docs/Dynamo-...leich_2008.pdf

(For power I'm using a XFDD hub dynamo marked as a 6V 2.4W device. I'm thinking of using something like maybe a luxeon star 45lm@350ma [1] unless there are better LEDs out there for this purpose)

[1] http://www.luxeonstar.com/luxeon-sta...50ma-p-219.php
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Old 10-29-08, 08:45 AM   #2
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Another thing to think about, LED flashlights are kind of right in the middle: Typically flashlights with the newer LEDS (XR-E, P7, MC-E etc...) are available much sooner and more affordable than bike specific lights. But like diy, this method is sometimes not as ideal from a form and function point of view as a dedicated bike light.

As for your dynamo, I think the Cree MC-E may work nicely with that but I'm not positive.

Top of the line bike lights seem to really project the best beam (see mechbgons secca 700 link) but you pay a high premium for that. When you compare what you can DIY or to a lesser extent, adapt a flashlight to do to a commercial product, the commercial product just can't compete at the same price range. Some lights such as the Airbike Everlight were kind of getting close, but now their prices are higher.

Last edited by Wiggle; 10-29-08 at 08:50 AM.
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Old 10-29-08, 08:47 AM   #3
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Doubled
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Old 10-29-08, 09:27 AM   #4
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You actually can get optics tailored for use on roads for DIY headlight projects. I use at least one Fraen 15X30 degree elliptical pattern optic in my headlight projects.
http://www.luxeonstar.com/fraen-lens...am-c-16_11.php
This optic produces a very nice pattern similar to that of an automotive headlight on low beam. If your going to build a single beam headlight this is the type of optic to use. It lights up the entire roadway with very little spill so as not to blind oncoming traffic. Addition of a second narrow beam optic allows for a second headlight configured as a "high beam" used for distant illumination. A switch allows selecting high, low, or both headlights combined. Here is a photo of a light utilizing both types of optics.

You can see the elliptical optic on the right and narrow beam optic on the left.


Here is a photo of a headlight using a single elliptical optic .
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Old 10-29-08, 10:36 AM   #5
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Ok. A lens is a good idea.

Looking around, some people seem to be using the Cree MC-E led. It is supposed to produce 370 lumens 350mA. Looking at the luxeon site, their leds seem to be around a tenth of that. Is it that the MC-E is newer and better, or is there some catch?

If I try and use the MC-E in the

http://pilom.com/BicycleElectronics/DynamoCircuits.htm

circuts, should I expect it to work?
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Old 10-29-08, 12:29 PM   #6
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Vf is different maybe?
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Old 10-29-08, 12:41 PM   #7
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The Cree MC-E has 4 LED dies in a single optic dome. If you look at the 4 LED circuit on Martins page (pilom.com) you'll find the circuit you need for using the new Cree MC-E. The MC-E has separate connections for all 4 dies (LED elements). You'll need a STAR mounting board so all the dies can be connected in series as shown in the 4 LED circuit. DX has Star mounted parallel connected MC-E LEDs but currently no series connected MC-E Stars. They do have series connected boards.
http://www.dealextreme.com/details.dx/sku.16544
This would require you order separate Star boards and MC-E emitters and solder them yourself. A difficult task for anyone without a special surface mount soldering equipment, tools, and experience. I'm too old to do surface mounting of tiny parts myself.
I'm sure they will eventually stock series connected MC-E LEDs as they would be perfect for automotive applications (14.8-volts) as well as for use with Martins bicycle dynamo circuits.
The latest generation of Cree and SSC LEDs are much brighter than those shown on the luxeon site. Luxeon has fallen far behind the LED output game.
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Old 10-29-08, 12:44 PM   #8
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Learning more, the downsides of the MC-E seem to be:
- more expensive
- more heat to dissipate
- harder to find good lenses for

So I guess I need to decide if the factor of four difference in luminosity overcomes this.
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Old 10-29-08, 01:40 PM   #9
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My previous post was before reading the most recent reply. Ok. So the other downside is that either they're in parallel (but then my hub can't give 350mA to all four) or they're in series (but then I have more work pedaling).

So something like the cree XR-E is more what I should be thinking of?
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Old 10-29-08, 02:01 PM   #10
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The MC-E is pretty good value if you need that much light(500 -600lm). This is enough for pretty much anything.
Its new enough that a good range of optics aren't yet available and the good ones are likely to be 30mm or more. Will be a nice solution once good optics and series boards are available(soon I hope).

I like the MR11 boards and optics from cutter.com.au. With Cree R2s they are the brightest/most efficient out there. They put out 500-650lm depending on if you're using the quad or triple led board (the new triple E3 puts out 500lm). Wire up using the circuits from pilom.com. Note that more LEDs means you need to be going faster to get the light going.

If you need less light a single cree led and optic do ok. This is way more light than most bikes have. Heres a simple build in this thread:
Blowing bulbs with a dynohub or will I fry an LED light?
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Old 10-30-08, 06:44 AM   #11
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Thanks znomit. I'll probably go with just the single cree, then.

(I've got the generator hooked up to a cheap chinese incandescent bike light right now. It's pretty dim. Definitely going to need to build my light soon with DST ending.)
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Old 10-30-08, 09:58 AM   #12
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Looking at cutter for cree XR-Es:

http://www.cutter.com.au/products.php?cat=48

I see the Q5 category, but I also see a more expensive R2 category. The binning information of Cree's site says nothing about an R2 category, but is it likely that the R2 bin is brighter than the Q5 bin?

Also, it talks about various W[X] "tints". I can read the definitions in the binning sheet, but it's hard to ground the numbers in reality. For bike lighting, do tints matter (are they all pretty close)? Is there something better than picking one randomly?
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Old 10-30-08, 10:08 AM   #13
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I found a CPF sticky on tints, so I'm ok for that.
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Old 10-30-08, 01:19 PM   #14
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Quote:
Originally Posted by cbr2702 View Post
Looking at cutter for cree XR-Es:

http://www.cutter.com.au/products.php?cat=48

I see the Q5 category, but I also see a more expensive R2 category. The binning information of Cree's site says nothing about an R2 category, but is it likely that the R2 bin is brighter than the Q5 bin?

Also, it talks about various W[X] "tints". I can read the definitions in the binning sheet, but it's hard to ground the numbers in reality. For bike lighting, do tints matter (are they all pretty close)? Is there something better than picking one randomly?
WH is a good bike light tint. Go for R2.
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Old 10-30-08, 01:32 PM   #15
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Thanks znomit. Ordered.
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Old 01-05-09, 07:57 AM   #16
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I've now been riding with my Cree XR-E R2 (WH) (with 10/40 elliptical lens) for a while now. I'm very visible and it's bright enough to see by if not going too fast. I like it a lot.

Thanks everyone.
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Old 01-05-09, 09:04 AM   #17
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Quote:
Originally Posted by cbr2702 View Post
I've now been riding with my Cree XR-E R2 (WH) (with 10/40 elliptical lens) for a while now. I'm very visible and it's bright enough to see by if not going too fast. I like it a lot.

Thanks everyone.
Congratulations. How about some pics of your setup and beam patterns?

I went the lazy route and got an IQ Fly. It's certainly not as bright as the DIY stuff people like yourself have cooked up, but it does have a couple advantages (beyond not having to do any work). First, the optics are amazing. The beam pattern illuminates the road uniformly, which I think makes it easier to see what's coming, even with less total brightness. Judging from the light reflected from road signs, I think I'm still adequately visible to oncoming traffic (maybe not side traffic, though). You just can't get that kind of optics for DIY, as far as I know. Second, the standlight function is nice for staying visible when waiting at stoplights. Full brightness for several seconds, followed by reduced brightness for a couple minutes. You can construct your own electronics for this, of course, but since I haven't seen any examples of this, I assume it's a bit complicated.

Anyway, it's always nice to see the latest DIY projects, so let's see more details when you get a chance!

Cheers.
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Old 01-05-09, 10:25 AM   #18
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Beamshots coming when I remember to bring the camera on the way to work. (And I need to do this some day when it's not icy like it is around now)

The optics are pretty good. No sharp edges or hotspots, no light wasted in the sky. But not the ideal light-at-the-top trapezoid that you get with the IQ-fly.

I didn't end up wiring a standlight. Or even a smoothing capacitor. Completely minimal. This does mean that the light goes off when I wait at an intersection and flashes at very low speeds. But the combination of these is actually nice: when I just start off across an intersection the flashing makes me very noticeable. I also ride taking this into account and avoid stopping, slowly approaching red lights. But I would do this anyway, as I do in a car, to avoid wasting momentum.
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