From: bestagentsNOSPAM@hotmail.com (Chris P)
Subject: Re: Best way to power array of LEDs?
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NNTP-Posting-Date: Sat, 12 Oct 2002 15:46:42 GMT
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Date: Sat, 12 Oct 2002 15:46:42 GMT
more and more vehicles are using LEDs for taillgihts - first
cadillacs, not busses and big trucks. traffic lights too. I assumer
longer life than a bulb?
as for wheher 3rd lights reduce accidents, i agree with your
statements, but add tis - with todays distractions (eating, cell
phones, etc) one is not paying as much attention as one should. SOO,
at night particulary, distinguishing the tail lgiht or brake light of
the car in front of you is easier since the 3rd lihgt instantly
identifies that the brakes are applied and it is not unusually bright
ofOn Sat, 05 Oct 2002 03:32:55 -0000, firstname.lastname@example.org
(Bob Wilson) wrote:
>In article <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net>,
>>Have assembled an array of LEDs for use as a 3rd brake light in my car,
>>configured as 4 rows of 9 jumbo LEDs, as of yet unwired. Of course the
>>supply will be 12 volts nominal (13.8 volts, maximum).
>>My options, as I see them, are:
>>1) Wire individual resistors to each LED based on its operating current
>>2) Wire each row in parallel and connect one resistor based on operating
>>current for 9 LEDs
>>3) Install voltage regulator to output voltage (ie, 1.3 volts?) to operate
>>all LEDs in parallel.
>>What is the best method to power these from an intermittent (whenever I
>>the brake pedal) power source?
>>Other options for powering this array?
>>Note that my return address is corrupted in an attempt to reduce spam. If
>>choose to e-mail me, please correct my address as described below.
>Not really rocket science.
>Point 2 and 3 (above) are electrically almost identical and won't work at
>all, unless all your LEDs are EXACTLY identical, and have the idential
>forward voltage over temperature. Not very likely.
>Point 1 will work just fine, but is hopelessly inefficient since
>approximately 90% of the power consumed will obviously end up as heat in the
>A simple solution would be to do a series-parallel arrangement and have each
>series string controlled by a single resistor. The aim is to have the
>forward voltage of each series string end up at around 10V or so, so that
>the majority of the power is actually dissipated by the LEDs, and not the
>As a side issue, one might well ask why bother to go to all this trouble to
>make something like a 3rd brakelight which is pointless as a safety device
>anyway. If one is actually close enough that the center light is more
>visible than the normal ones, you're gonna hit the guy ahead anyway. The
>only so-called research that was done to justify these things was done
>before car makers were forced to install them, and they were a novelty that
>got noticed. Now that they are on every car, no one takes notice of them.
>There is no statistical evidence that has shown that these things have
>reduced rear-enders, that I'm aware of. Well, I suppose there are those that
>claim that the fast response of LEDs (a mere 50 to 100 mS faster than normal
>brakelights) will prevent accidents, but then there are also those that
>claim to cows can fly, as well.
Life is hard.
Life is harder when you're stupid.