Re: [EVDL] LED Taillights - a money saver in gas cars? -rangeextenderin EV's? - an an - DIY Electric Car Forums
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Old 09-26-2007, 06:19 PM
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Default Re: [EVDL] LED Taillights - a money saver in gas cars? -rangeextenderin EV's? - an an

Well lemme point out something else.
Unless you have a buck converter, the red 3W LED is like 3V @ 1A. But
we start with a 13.8V system, so we have to burn off 10.8W in a huge
resistor.
Maybe you do have buck converter in there and if so great.

With multiple LEDs, the situation is simpler. We can put 3x in series
for a 9V forward voltage and the ballast resistor only needs to absorb
4.8W.

The 7.6mm P4 pks are easy to use IF the red lens is screwed onto the
back half. If the whole thing's one glued together piece and the bulb
is socketed through the back, we may have a problem.

But let's say the lens does unscrew. What we can do is get some
prototyping PCB from Radio Shack that is nothing but a grid of holes and
copper pads. The P4's pins are 2 holes apart. If it's the board the
with square pads, you can forgoe the wiring and just glob a lot of
solder to bridge pads to make a trace. So cut the board to a shape that
fits in there, make a few strings of 3 each string with a proper series
resistor and put those strings in parallel. I'm not sure how many P4s
it takes to make a taillight but I believe around a dozen P4s at their
max continuous current rating would be quite powerful and viewable in
full sun.

In many flashlights with elliptical silvered reflectors, those odd "side
emitter" Luxeon emitters actually cast a better pattern than the
standard Lambertian emitter because the beam is shaped according to the
reflector's design, not the wide Lambertian distribution. That might
make a side emitter better for those housings where you can't separate
the lens and put in a P4 board AND there's a silvered reflector but I'm
not sure.

Danny

Paul wrote:

>[quote] Danny Miller wrote:
>
>
>
>>A 3W red Luxeon sounds excessive for a taillight.
>>
>>
>
>Yes, I was looking at the 1157 replacement. It uses the Luxeon at a
>much lower power level for the tail lights and full power for brake
>lights.
>
>
>
>>Lumens are different in 2 ways. First off a white taillight bulb may
>>produce 400 lumens of white, but the red filter only makes the
>>light red
>>by blocking more than 2/3rds of the light energy because the blue and
>>green components are useless (a filter does not change photons of one
>>wavelength into another).
>>
>>Then the bulb throws those remaining lumens at 360 deg. Half will
>>strike the back, which may be silvered so at least some of it will end
>>up getting thrown forward again.
>>
>>
>
>A couple of very good points. I may get as much red light out the
>lens with 240 lumens of red LED with a 130 degree spread as I can get
>with a 1157 bulb. The question becomes how much of the light from an
>incandescent tail light is wasted. Car tail light bulbs are generally
>"warm white." Just how much is red, and how much the reflector
>looses, are questions I haven't found any documented answers to.
>
>
>
>>It is possible for an LED to be excessively bright only in the center.
>>Even in "wide" spread LEDs, like 130 deg, the intensity is greater
>>straight ahead, decreasing substantially as angle increases. This can
>>result in a very bright spot projected onto the middle of a
>>taillight lens.
>>
>>Multiple 7.6mm P4 pkg are a really good option. They get used a
>>lot in
>>commercial taillights. Since the pkgs can be spread out, they won't
>>make a single bright spot. There's also far less thermal issues when
>>it's done this way.
>>
>>
>
>There will be no cutting up of '66 Datsun tail light assemblies!
>Either it works acceptably well (equally bright, not to directional,
>not to "spot light") or I put the 1157 bulbs back in. I have looked
>at LED bulbs for it, but its not the current priority. Its a garage
>ornament at this time and that needs to be taken care of before I can
>really rate the effectiveness of LED bulbs for it. (real world with
>my wife following me)
>
>Thanx,
>Paul Gooch
>
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>
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>

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