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'[EE]: Automobile LED headlights'
2006\11\01@152306 by Charles Craft

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Interesting - I would have figured they would be wired so that multiple failures still allowed the lamp to function.

http://www.usatoday.com/money/autos/2006-10-31-headlight-usat_x.htm

<snip>

The National Highway Traffic Safety Administration says LED headlights are legal if they meet the illumination regulations applied to all other types of headlights in the USA.

They also have to be wired so that if one tiny LED fails, the whole light goes out. NHTSA says that prevents motorists from unknowingly driving with reduced illumination.

<snip>


2006\11\01@160853 by Peiserma

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piclist-bounces@mit.edu wrote:
> They also have to be wired so that if one tiny LED fails, the
> whole light goes out. NHTSA says that prevents motorists from
> unknowingly driving with reduced illumination.

So they prefer driving with no lights over dim lights? Hmmm.

On a distantly related note: car problems forced me to tear into my dash
yesterday. My remote-starter unit dated 1993 is controlled by a
PIC16C54...




2006\11\01@162523 by PicDude

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On Wednesday 01 November 2006 14:23, Charles Craft wrote:
> ...
>
> They also have to be wired so that if one tiny LED fails, the whole light
> goes out. NHTSA says that prevents motorists from unknowingly driving with
> reduced illumination.

Very odd, I would've expected that considering the cost of the LEDs, adding
some monitoring to indicate blown LED-string(s) would've been relatively
insignificant, and would be safer (IMHO) if you blow one LED on a dark road
in the middle of nowhere some night.  The NHTSA should've at least allowed
this option.

Cheers,
-Neil.

2006\11\01@195046 by Sean Schouten

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On 11/1/06, PicDude <spam_OUTpicdude2TakeThisOuTspamavn-tech.com> wrote:
>
>
> Very odd, I would've expected that considering the cost of the LEDs,
> adding
> some monitoring to indicate blown LED-string(s) would've been relatively
> insignificant, and would be safer (IMHO) if you blow one LED on a dark
> road
> in the middle of nowhere some night.  The NHTSA should've at least allowed
> this option.
>


Well... in that single scenario, a BIG plus would be that a car has not one,
but two headlights. Still a bummer though!


Sean.

2006\11\01@220012 by Jim Korman

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Charles Craft wrote:
> Interesting - I would have figured they would be wired so that multiple failures still allowed the lamp to function.
>
> http://www.usatoday.com/money/autos/2006-10-31-headlight-usat_x.htm
>
> <snip>
>
> The National Highway Traffic Safety Administration says LED headlights are legal if they meet the illumination regulations applied to all other types of headlights in the USA.
>
> They also have to be wired so that if one tiny LED fails, the whole light goes out. NHTSA says that prevents motorists from unknowingly driving with reduced illumination.
>
> <snip>
>
>
>  
I note in the article they mention the long life time of an LED.
BUT, if one LED fails the unit, what does that do to the
potential life span of the unit?

Jim

2006\11\01@222731 by David VanHorn

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>
>
> I note in the article they mention the long life time of an LED.
> BUT, if one LED fails the unit, what does that do to the
> potential life span of the unit?


Makes it much less reliable.

I smell special interest intervention here..


If I had a headlight with a significant number of LEDs in it, and I found
out that I had to replace the whole thing because ONE blew, I'd be pissed.
If you have 10 leds, then that's only 10% down if one fails, and even a
slightly dirty headlight is down that much.

2006\11\01@223053 by David VanHorn

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www.usatoday.com/money/autos/2006-10-31-headlight-usat_x.htm

gargoyle delivered this link along with this email discussion.

2006\11\01@223439 by Herbert Graf

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On Wed, 2006-11-01 at 22:27 -0500, David VanHorn wrote:
> >
> >
> > I note in the article they mention the long life time of an LED.
> > BUT, if one LED fails the unit, what does that do to the
> > potential life span of the unit?
>
>
> Makes it much less reliable.
>
> I smell special interest intervention here..
>
>
> If I had a headlight with a significant number of LEDs in it, and I found
> out that I had to replace the whole thing because ONE blew, I'd be pissed.
> If you have 10 leds, then that's only 10% down if one fails, and even a
> slightly dirty headlight is down that much.

Well, the way I see it is as long as the headlight outputs at least the
minimum required amount of illumination you are OK.

So, design the headlight to put out say 150% of the minimum, then you
can have 33% of the LEDs fail before you're required to "shut off" the
headlight.

TTYL

2006\11\01@224954 by David VanHorn

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Article said they would cost even more than the HID lights.
OUCH!

2006\11\02@003936 by Tony Smith

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{Quote hidden}

David might be right.  Current regulations are that the headlight must
illuminate to a certain distance, 30 metres or so.  Here's a US article that
says 15 feet - http://www3.whdh.com/features/articles/hank/30/.

There's no reason to fiddle with the existing rules.

I think it's far safer to have a slightly dimmer light than no light at all.
Also, it works both ways, people can see the car with the lights on.

Might be a moot point eventually as LEDs get brighter.

Tony

2006\11\02@114537 by Mike Hord

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> If I had a headlight with a significant number of LEDs in it, and I found
> out that I had to replace the whole thing because ONE blew, I'd be pissed.

No, you (being who you are) would crack it open, pull the LED, and replace
it from one purchased at Digikey.  As would (I hope) most of us.

A friend of mine did this with his brake light strip.  It was one of those with
LEDs, and he found the faulty one and replaced it.

I agree that it is kind of stupid- to me, part of the point of using a multi-LED
bank is redundancy against failure.  I'd say it should be designed with a
couple of extra LEDs (??? how many are we talking about, here?) which
kick in upon failures to keep the light level up, but below a certain point,
the whole thing dies.

Mike H.

2006\11\02@120237 by David VanHorn

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On 11/2/06, Mike Hord <.....mike.hordKILLspamspam@spam@gmail.com> wrote:
>
> > If I had a headlight with a significant number of LEDs in it, and I
> found
> > out that I had to replace the whole thing because ONE blew, I'd be
> pissed.
>
> No, you (being who you are) would crack it open, pull the LED, and replace
> it from one purchased at Digikey.  As would (I hope) most of us.


This could end up like toner carts, with embedded uPs working to prohibit
such a repair, or a hardware solution that fries all the other leds.

I agree that it is kind of stupid- to me, part of the point of using a
> multi-LED
> bank is redundancy against failure.  I'd say it should be designed with a
> couple of extra LEDs (??? how many are we talking about, here?) which
> kick in upon failures to keep the light level up, but below a certain
> point,
> the whole thing dies.


Yeah, that's how I'd do it.. In a smart car, the headlight could in theory
communicate it's status, and warn that it's run out of spare LEDs, or
something like that.

2006\11\02@120812 by Michael Rigby-Jones

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{Quote hidden}

Christmas tree lights manage this without any extra circuitry.  They even kill themselves after too many bulb have blown!

Regards

Mike

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2006\11\02@130132 by David VanHorn

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>
> Christmas tree lights manage this without any extra circuitry.  They even
> kill themselves after too many bulb have blown!


True, but the filament lets go and allows the supports to spread and contact
a ring of wire.
Can't do that in an LED.

2006\11\02@155718 by Shawn Wilton

picon face
I sense an emerging business opportunity repairing expensive LED headlights
on the cheap!



On 11/2/06, David VanHorn <EraseMEdvanhornspam_OUTspamTakeThisOuTmicrobrix.com> wrote:
{Quote hidden}

> -

2006\11\02@201156 by Michael Rigby-Jones

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>-----Original Message-----
>From: piclist-bouncesspamspam_OUTmit.edu [@spam@piclist-bouncesKILLspamspammit.edu]
>Sent: 02 November 2006 17:19
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE]: Automobile LED headlights
>
>
>>
>> Christmas tree lights manage this without any extra circuitry.  They
>> even kill themselves after too many bulb have blown!
>
>
>True, but the filament lets go and allows the supports to
>spread and contact a ring of wire. Can't do that in an LED.
>

I knew how it worked, was just joking really.  However, given the very high cost of these headlights, some "smarts" to alert the driver to a failed array of LEDs really should have been included.  It could even throw up a fault code on the OBD system.

Cheers

Mike

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2006\11\02@201451 by Russell McMahon

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> I agree that it is kind of stupid- to me, part of the point of using
> a multi-LED
> bank is redundancy against failure.  I'd say it should be designed
> with a
> couple of extra LEDs (??? how many are we talking about, here?)
> which
> kick in upon failures to keep the light level up, but below a
> certain point,
> the whole thing dies.

One out all out can also be viewed as stupidly PC.
Tungsten bulbs degrade in output across lifetime with no suggestion
that they must be replaced prior to absolute failure. That said a
fully parallel LED array may take decades of use to dwindle to the
all-out point.



       Russell

2006\11\02@224240 by Tony Smith

picon face
> David might be right.  Current regulations are that the
> headlight must illuminate to a certain distance, 30 metres or
> so.  Here's a US article that says 15 feet -
> http://www3.whdh.com/features/articles/hank/30/.


Sigh.  115 feet.  Doh.

And in addition, I don't think headlights are tested in Australia either.
Their aim is checked, but I'm not sure on brightness.  How hard is it to
wave a lux meter around?

Tony

2006\11\03@004740 by Mario Mendes

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>> David might be right.  Current regulations are that the
>> headlight must illuminate to a certain distance, 30 metres or
>> so.  Here's a US article that says 15 feet -
>> http://www3.whdh.com/features/articles/hank/30/.
>
>
>Sigh.  115 feet.  Doh.
>
>And in addition, I don't think headlights are tested in Australia either.
>Their aim is checked, but I'm not sure on brightness.  How hard is it to
>wave a lux meter around?
>
>Tony


How hard???  Well, I estimate that it'll take 356 government employees, 67
months to write hundreds of pages to document the what/why/when/where/how to
do it and cost millions in taxes just because someone decided it needed to
become a law/regulation.

No offense to any government workers in the list (if any) of course ;)


-Mario




2006\11\03@035930 by Howard Winter

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Tony,

On Thu, 2 Nov 2006 16:58:08 +1100, Tony Smith wrote:

{Quote hidden}

Over here headlight alignment is checked on a machine but not brightness, but they did mention on my car's last test that they were dimmer than
they should be - I suspect a dodgy earth connection - but they didn't fail it, and as long as they are substantially working I don't think they can.  I
know they can fail it for being *too* powerful - I believe 55W is the limit, but you can get 100W bulbs "for offroad use only".

Cheers,


Howard Winter
St.Albans, England


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