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Re: [EVDL] LED Taillights - a money saver in gas cars? -rangeextenderin EV's? - an an

Since I have the exact bulb you are referring to should I try to get
pictures of an incandescent bulb and the 3W LED in the same tail
light? I guess I could set the camera at the same settings to make a
fair comparison. Remember that the lumen spec on this red led only
will see that particular wavelength whereas the lumen spec on a
regular bulb will include all wavelengths in a broader spectrum.

David Nelson

On 9/26/07, Paul <[email protected]> wrote:
> First off I should point out that I misquoted the specs <http://
> www.superbrightleds.com/specs/115x-xLX3.htm>. I was looking at the ma
> column instead of the lumens column. At full brake light power it
> draws 240ma (current regulated.) That would be 2.88 watts of power
> for the brake light function at 90 lumens. That is a lot less than
> the 400 lumens of a 1157 bulb with both filaments lit.
>
> I've tested a few cheap LED auto bulbs and found them lacking (not to
> bright unless you are right in the center.) I have not yet tested
> this bulb (I've been mostly occupied with the actual conversion of my
> '66 Datsun right now, plus its not a cheap LED bulb.)
>
>
Danny Miller wrote:
>
> > 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.
>
> Look at the specs on the LED replacement bulb I was proposing. Try
> finding lumen specs for cheap LED auto bulbs (I didn't have any
> luck.) It is current regulated and mounted in a heat sink. It would
> be internally dissipating 2.88 watts in the brake light condition if
> the LED didn't convert any to light (note the .24 amps at 12 volts
> spec.) I know that an incandescent bulb converts about 90% of the
> applied power to heat (good ones are in the 80's, but this isn't a
> "good" example.) So I can expect a 1157 bulb to make around 18 watts
> of heat (and 2 watts of light - to be filtered and reflected.)
>
> Using resistors as your voltage drop is not so simple. How many LEDs
> do you want in series? 3 is typically less than 6 volts (for red
> LEDs.) You would still be dropping 1/2 the voltage across each
> resistor (around 1/8 watt per 3 LEDs, times HOW many?). If you put
> more in series the current drops pretty quickly as the voltage drops;
> the result is an LED lamp that dims about as fast as the incandescent
> one (the incandescent bulb shifts toward red as the voltage drops.)
>
> > 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.
>
> That package may be easy but how easy is it to find replacement tail
> light housings for a 1966 Datsun 411? I'm *not* going to hack my tail
> lights; I would rather run 1157 bulbs (it has kept the car intact for
> over 40 years now.)
>
> Paul Gooch
>
> P.S. - there is no significant power savings in LED illumination for
> on-road EVs at this time. The only advantage is faster brake lights.
> That is nothing if they don't notice them!
>
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