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tekochip
User Rank
Platinum
Re: Not the only GM LED problem
tekochip   6/25/2012 11:45:14 AM
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That's a darn good question Finnicky. The human eye has quite a bit of persistence, meaning that when we see a bright light for only just a moment we perceive the light for a little bit longer than that. This, of course is the way TVs and movies work by showing an image for only a fraction of a second and then displaying the next image for a fraction of a second. To our eyes the image has been on constantly. Back to the brake lights; if they were on solid the LEDs would have to be run at a lower current and lower brightness to not exceed the maximum average power dissipation, but if the LEDs are strobed a much higher current and brightness can be used and the human eye will perceive a higher brightness than if the LEDs were on solid.


creamysbrianna
User Rank
Silver
Re: Me, too!
creamysbrianna   6/25/2012 11:22:46 AM
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@Analog Bill this is around the time that the big three stoped caring about quality and more about profits.  Today they care more about creating the latest and greatest fluff features within the cabins of their vehicles than the quality of the parts that really truely matter.

I had a 1983 Pontiac Grand Prix which ultimatly died due to a rear main seal failure that I unfortuantly didn't notice soon enough to prevent the bearings from failing.

1988 buick skylark: went throught about three alternators and starters, one day the engine died at a light and had it sent to the shop come to find out the timing belt failed.  It was supposed to be changed every 50k I have to admit it lasted least 100k before failure. 

Then there was the 1994 caviler that shot two spark plugs out of the head and caused the threads to break.

After that I never bought another big three car again.  My 2001 honda civic is still running with 205k on it with no major failures with the engine or engine assesories.

The big three understand the "faster and cheaper" part of the "better, faster cheaper" manufacturering mantra but still can not figure out the "better" part still.  There is a reason why Toyota held #1 in sales for almost a year, they make a better quality vehicle than The Big Three.  For those who think Toyota is not made here they have three or four final assembly plants here.  Second the big three likely don't have more than 50-60% ameriacan content in their vehicles so they are gradually becoming imports themselves as well.

shjacks45
User Rank
Bronze
Dead Leds
shjacks45   11/21/2011 5:09:29 AM
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Local transit authority tested some tail lights and brake lights. Several older designs used Red LEDs ~.7 V at current and enough of them to make 12V and a small value resistor. If one LED fails open then no light. if one fails short than the higher current eventually causes future faiures. The best ones had many parallel LED strings so that the Brake lights still had adequate light to meet State standards even though you could see multiple LEDs had failed. Failure cause? Vibration, contamination, heat, voltage spikes (40 V from 12 V nominal system), light (LEDs are photosensitive, damaged by radiation)?

LED damage by heat can be lessened by pulsing them. Commercial vehicles, where pulsing was tried as a safety measure, pulse when brake pedal applied, but stopped use air e-brake. Auto requires keeping foot on break pedal at stop light.

Having designed with Laser diode (LEDs): light emission declines over time as carrier availability declines, partly due to temperature and in part by photons; laser diodes often had an included photodiode to provide feedback; light emission increases as an exponent of current (some ordinary LEDs will 'Lase', emit coherent radiation, at higher currents) hence low duty cycle pulsed LEDs are more efficient and generate less damaging heat; also deterioration of phosphor in white LEDs;  .

Reason for design emphasis is that most contemporary LED lighting uses a series string of white LEDs and a (direct current) current limited switching regulator.in other words designs are more sophisticated and more failure prone.

There are more reasonably priced third party replacements that are less expensive than the time to do diagnostics.

 

shjacks45
User Rank
Bronze
Dead Leds
shjacks45   11/21/2011 5:09:08 AM
NO RATINGS
Local transit authority tested some tail lights and brake lights. Several older designs used Red LEDs ~.7 V at current and enough of them to make 12V and a small value resistor. If one LED fails open then no light. if one fails short than the higher current eventually causes future faiures. The best ones had many parallel LED strings so that the Brake lights still had adequate light to meet State standards even though you could see multiple LEDs had failed. Failure cause? Vibration, contamination, heat, voltage spikes (40 V from 12 V nominal system), light (LEDs are photosensitive, damaged by radiation)?

LED damage by heat can be lessened by pulsing them. Commercial vehicles, where pulsing was tried as a safety measure, pulse when brake pedal applied, but stopped use air e-brake. Auto requires keeping foot on break pedal at stop light.

Having designed with Laser diode (LEDs): light emission declines over time as carrier availability declines, partly due to temperature and in part by photons; laser diodes often had an included photodiode to provide feedback; light emission increases as an exponent of current (some ordinary LEDs will 'Lase', emit coherent radiation, at higher currents) hence low duty cycle pulsed LEDs are more efficient and generate less damaging heat; also deterioration of phosphor in white LEDs;  .

Reason for design emphasis is that most contemporary LED lighting uses a series string of white LEDs and a (direct current) current limited switching regulator.in other words designs are more sophisticated and more failure prone.

There are more reasonably priced third party replacements that are less expensive than the time to do diagnostics.

 

FinnickyFinn
User Rank
Silver
Re: Not the only GM LED problem
FinnickyFinn   11/19/2011 9:08:22 AM
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I wonder why they strobe the break lights anyway. Why not turn the LEDs on solid. That will make for a much simpler circuit and less chance to break. My guess is that in this case it is not the LEDs that broke, but the electronics packaged into the unit. Still, should have lasted much longer than it did.

Alexander Wolfe
User Rank
Blogger
LEDs are supposed to have long lives
Alexander Wolfe   11/16/2011 8:41:55 AM
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This experience is counterintuitive. LEDs are supposed to be long-lived. Is this some kind of over-voltage situation? If you want to hear some interesting stuff about LEDs in tech usage, check out the archive posting of a Design News Radio event I did with LED expert Carol Lenk, How LEDs Are Changing Embedded Design.

sesterza
User Rank
Iron
how long the LED lived?
sesterza   11/5/2011 6:43:10 PM
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how long the brake light on 2006 Tahoe did work? Five year, maybe 20 kmiles/year, maybe 50 MPH mean speed: it means 2000 hours of car service but only few % of brake light on, can we say 10% duty? sure much less but even 200 hours of brake light life make me crazy!

MIROX
User Rank
Platinum
Re: Center taillight failure
MIROX   11/3/2011 2:32:53 AM
NO RATINGS
Definitely FILE a complaint with NHTSA here is the link:

https://www-odi.nhtsa.dot.gov/ivoq/

Requirements:

1.) You must be the vehicle owner, complaints from 3rd party will be disregarded, but you not need to be original owner, just current owner, no time or mileage  limit

2.) YOU MUST have the VIN, Date of Occurence and vehicle odo mileage if any is missing it it not a valid complaint

3.) There is no limit (time or miles) on safety issues, even out of OEM Warranty complaints are valid, and MFG will have to recall or reimburse owners if there is recognizible safety defect trend.

However there also is no $ limit on how much OEM can charge for any replacement item, if they choose to charge you $1,000 for a bulb they can and in most cases will get away with t if people do not file direct complaints.

 

NHTSA does not have personall to monitor web or police the OEMs

 

 

 

 

izzyizzo
User Rank
Iron
Not the only GM LED problem
izzyizzo   11/2/2011 9:11:55 PM
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Until very recently, GM OEM LEDs pulsed at a low enough frequency for some people to see the strobing or ghosting. Though it appeared to affect only a small number of motorists, those who are sensitive to the strobe rate can be distracted such that safe driving becomes difficult. (I can see it, and it makes me crazy.)

Flicker is evident on some other makes, but GM is the worst -- and Cadillac the worst of that bunch.

GM has repeatedly denied "going cheap" on its LED strobe, but proceeded to solve the supposed non-problem somewhere around the 2010-09 model years. But plenty of the old LEDs remain on the road. While it's unfortunate for GM owners that the offending LEDs are going bad, it's good news for those of us whose safe driving is impacted by poor GM quality.

Besides... I'd imagine GM owners are used to design flaws by now. :) 

William K.
User Rank
Platinum
Short life of GM leds
William K.   11/2/2011 8:08:47 PM
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I agree that the best thing would be to open the assembly and find the problem, and then repair it. My guess is that it is a poor quality LED that is opening up the series string. Bright red LEDs are widely available from many sources, so getting a replacement will not be that hard. The important part of th task will be setting the current to the correct value. Since efficiency is not the main goal, using dropping resistors would be the best choice.

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