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hmmm.
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Discussion Starter · #1 ·
After getting caught out in the dark a few times with no light, I decided a taillight would be in order. Instead of the usual light mounted on the seatpost, I was hoping it would be possible to make a more "factory" looking setup. If it's possible, I'd like to mount an LED on the inside of the reflector holder. (picture attached) The issue is that the light has to shine through a reflector. I was wondering if this would work or not. I would've already ripped into it and tried it, but the bike is 40 years old, so spares aren't readily available, to say the least. If the light can properly shine through, would I use a white or red light? Thanks.
 

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This is an idea i considered myself many moons ago,
BUT, there is no side visibility,
too much messin with batteries,
wires and switch ........
add to this that a blinky rear light is very inexpensive these days and
much more visible .....
The bottom line is, it`s not worth it !!
 

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hmmm.
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145 Posts
Discussion Starter · #3 ·
Yeah, I guess the side visibility would be pretty poor. The wiring isn't a problem for me, but if the the light isn't safe perhaps it would be a better idea to just go with the standard seat tube type. It'd still be fun to try, though.
 

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I have the exact same reflector and have had the same thought. From a functional perspective, Hendo's right - modern blinkies are cheap and effective. But from a style perspective, this one wins. My gut feeling is that a red LED would work better/brighter, but you could try hacking apart a modern red reflector and shine different LEDs through it to check. If the reflector doesn't allow enough light through it, you could replace the reflector with a round piece of red plexiglass - obviously it'd lose its reflective properties but the LED would be brighter and it'd still look close to original.
 

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Before you buy any specific LEDs or drivers you might want to look at my experiments with tail lights. The driver that was recommented to look at will not blink and will most likely be to much for the led. You will need some type of heat sink. Check out my site. http://www.kayakaccessri.info/krabachwebsite/bike_light/bike_light_project/intro.html (Dont let the kayakaccessri fool you, I had to temporarily stick the bike light project there.)
Specifically the flasher lights starting with prototype 10. There is alot of info that I gleaned from putting together the flashers. You might get some ideas how to convert the reflector. I have the same fender and reflector on my antique 72' Motobecane Grand Record.
 

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hmmm.
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145 Posts
Discussion Starter · #11 ·
Wow, that's a lot of good information on your site. I wasn't sure whether or not to make the light blink, because, of course, car lights don't blink and neither do motorcycle lights. Also, I doubt that it'll need a heatsink because the longest I ever plan on using it at a time is 45 minutes or so. Thanks for the website link :)
 

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Lets RIDE!
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mkrabach said:
The driver that was recommended to look at will not blink and will most likely be to much for the led. You will need some type of heat sink.
I meant to add more info but it was xmas eve and my wife as bugging me to stop wasting time on the computer :)

The r/o Lux III leds are rated up to 1540mA, so that driver is fine, and you'll gen close to max brightness. I have that exact led/driver combo wired up on my workbench right now, and I've run it for half an hour without getting hot. It IS screwed down to a 3" square of .125" aluminum which heatsinks it nicely, getting just slightly warm. Regarding the heatsink issue: if run on it's star base only, it gets quite hot very quickly. All high-power leds need to be fixed to a heatsink. What I'm thinking in your situation is if it could be fixed to a disc of aluminum that was also in solid contact with your fender, you'll have a big heatsink that's air-cooled as you ride, so no problems with overheating. Troutie has been successfully running multiple high-power leds using the handlebars as the heatsink, so I don't see why the fender wouldn't work.

mkrabach is correct that this driver has no blinking mode, which is great for being seen on a bike. There is another DX driver which has blinking modes. It is regulated to 1000mA, which is still bright with the this led....I've tested a Lux III on a 1000mA buckpuck driver and it's real bright. There's even a way of wiring the 5 mode and the 1400mA drivers together to get blinking modes at 1400mA, if you want to get complicated.

The other drawback of these drivers is their small input voltage range....something like 3 - 4.5v max if I recall.

You might also want a wide angle optic behind your reflector, to get more of the light going where you want it.

All in all, it could be fun project, but a good blinky tail light mounted under the seat would be way quicker and cheaper.
 

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I took a closer look at that reflector and honestly I don't think it'd be a good host - it's a reflector encased in a rubberized housing. There's not nearly enough room for an LED, driver and secondary optic, and even if there were, there's no good thermal path for heatsinking.

Another option for an old school look would be to use the rear light housing from old generator light set.

Here's one I have I'm considering modding - https://i44.tinypic.com/nqoh2g.jpg.
 

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hmmm.
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Discussion Starter · #14 · (Edited)
Using the fender as a heatsink is a good idea. Also, to address the issue of space, I was planning on mounting only the LED inside the reflector housing- everything else would go inside the fender itself. As far as heatsinks go, would it be necessary to have it attached to the fender? I'm not so sure that would be possible. I do have some smalled finned heatsinks sitting around that I could attach to the LED. Thanks for the driver link as well.

EDIT: Crap.. Just opened up the reflector and there's a metal plate backing the reflector itself. I think the better idea at this point would be to find a round blinky light, paint the casing white, and figure out how to mount it on the fender. But thanks for the info all the same guys!
 
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