Intrepid High Mount Stop Lamp LEDs?

What are the pros and cons of using red LEDs instead of light bulbs for the center high mount stop lamp (on the deck lid) for an Intrepid? Since this location is subjected to vibration everytime the trunk is closed, LEDs should be more suitable. Also, LEDs illuminate sooner allowing faster reaction time for the driver behind you.

The CHMSL bulb number is 912. I've seen LEDs with other numbers that claim to fit 912 (and a bunch of others) but I havent yet seen a 912 LED so I'm not sure.

Is this a bad idea or is there a part number out there that I should look at?

Thanks.

Reply to
Greg Houston
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Pro: The vendor who sells you the LEDs makes lots of money. Con: Your center brake light no longer works as intended, particularly from the standpoint of visibility angles (horizontal and vertical).

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LED signalling lamps (brake, tail, turn...) are appearing on cars, and are widely used on trucks, but it really is not a "retrofit" item in the sense you're thinking of. The rear lamps of your car rely on a point source of light (glowing filament), collecting that light with a parabolic reflector and dispersing it with pillow optics in the lens. An LED is a vastly different *kind* of light source. Unlike a glowing filament, it does not produce light in an even sphere. Instead, it projects a very narrow beam of light in ONE direction. That's why these so-called "LED retrofits" consisting of a 1" diameter matrix of LEDs on a bayonet or wedge base are unsafe; there's no way you can get enough light through a wide enough angle (horizontally and vertically) to create a safe and legally-compliant lamp. There are other considerations, too -- it is tricky to get the right ratio of bright-to-dim intensities both on axis (straight behind the lamp) and also through the entire vertical and horizontal beam spread.

Look at the optics of the Cadillac DeVille that has Hewlett-Packard LED tail/brake lamps, or the high-end Mercedes S-class that has LED brake lamps. You'll see some *very* fancy optics used to coordinate the light from a *LOT* of LEDs to get everything right in terms of brightness in both dim and bright mode, uniformity of brightness throughout the visibility angles required by law, ratio of intensity between "bright" and "dim" mode, etc. These kinds of optics are not something you can kludge in your garage, let alone achieve with these unsafe "retrofits".

The important thing to remember is that you're working with safety systems everyone else on the road relies upon.

Reply to
Daniel J. Stern

Good information, thanks for taking the time to reply. It doesn't sound like that good of an idea, although I admit I first became suspicious when I saw one model of LED 'bulb' that was supposed to fit half a dozen of bulb numbers. Who standardized bulb sizes with common numbers? SAE?

Still, I wish Chrysler had used LEDs for this application, particularly for the quicker illumination and every time someone slams the trunk shut the bulbs get slammed too. I do see a lot of non-functioning CHMSLs and eliminating a bulb that can (will) burnout could be a design improvement. Perhaps the technology will be better/cheaper in the future.

Reply to
Greg Houston

| > > What are the pros and cons of using red LEDs instead of | > > light bulbs for the center high mount stop lamp (on the deck | > > lid) for an Intrepid? | >

| > Pro: The vendor who sells you the LEDs makes lots of money. | > Con: Your center brake light no longer works as intended, particularly | > from the standpoint of visibility angles (horizontal and vertical). | >

| > Canned text follows: | >

| > LED signalling lamps (brake, tail, turn...) are appearing on cars, and are | > widely used on trucks, but it really is not a "retrofit" item in the sense | > you're thinking of. The rear lamps of your car rely on a point source of | > light (glowing filament), collecting that light with a parabolic reflector | > and dispersing it with pillow optics in the lens. An LED is a vastly | > different *kind* of light source. Unlike a glowing filament, it does not | > produce light in an even sphere. Instead, it projects a very narrow beam | > of light in ONE direction. That's why these so-called "LED retrofits" | > consisting of a 1" diameter matrix of LEDs on a bayonet or wedge base are | > unsafe; there's no way you can get enough light through a wide enough | > angle (horizontally and vertically) to create a safe and legally-compliant | > lamp. There are other considerations, too -- it is tricky to get the | > right ratio of bright-to-dim intensities both on axis (straight behind the | > lamp) and also through the entire vertical and horizontal beam spread. | >

| > Look at the optics of the Cadillac DeVille that has Hewlett-Packard LED | > tail/brake lamps, or the high-end Mercedes S-class that has LED brake | > lamps. You'll see some *very* fancy optics used to coordinate the light | > from a *LOT* of LEDs to get everything right in terms of brightness in | > both dim and bright mode, uniformity of brightness throughout the | > visibility angles required by law, ratio of intensity between "bright" and | > "dim" mode, etc. These kinds of optics are not something you can kludge | > in your garage, let alone achieve with these unsafe "retrofits". | >

| > The important thing to remember is that you're working with safety systems | > everyone else on the road relies upon. | | Good information, thanks for taking the time to reply. It doesn't sound | like that good of an idea, although I admit I first became suspicious when I | saw one model of LED 'bulb' that was supposed to fit half a dozen of bulb | numbers. Who standardized bulb sizes with common numbers? SAE? | | Still, I wish Chrysler had used LEDs for this application, particularly for | the quicker illumination and every time someone slams the trunk shut the bulbs | get slammed too. I do see a lot of non-functioning CHMSLs and eliminating a | bulb that can (will) burnout could be a design improvement. Perhaps the | technology will be better/cheaper in the future. |

I thought that impact shock wasn't much of a problem unless the lamp filament was illuminated. I wonder how often the trunk lid is closed while the brake light is on (probably does happen occasionally).

Reply to
James C. Reeves

That's the second time you mentioned the LED being quicker. While it is indeed quicker, I don't think that is significant in reaction time. An incandescent takes, what, 20 or 30 mS to light up? That's kind of like saying that the reason you have to protect your skin more from the sun in Denver is because you're a mile closer to the sun than you would be at sea level (92,999,999 vs. 93,000,000 miles). 8^) (BTW, you do have to protect your skin more in Denver, but not for that reason - just thought I'd say that too before someone misunderstood and felt compelled to point that out.)

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

The time difference between bulbs and a center LED was just something that I noticed while noticing the car in front of me for several traffic lights the other night. :) I guess I'm just tired of replacing those two CHMSL bulbs (the left and right stop lamps are still the originals) and thought this might be something that LEDs can do better. But Dan's advice was very helpful and I bought some more 912 light bulbs. :)

Reply to
Greg Houston

It certainly is.

200mS to full intensity, vs. >2mS to full intensity for an LED. Do the math.

DS

Reply to
Daniel J. Stern

A kilopardon. You are correct.

According to this article, and as would make sense, it's not only the delay itself, but the sudden turn on seems to grab attention quicker too (i.e., reaction time, though the persistence of the human eye would reduce, but not eliminate, the effect):

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The 200mS is probably a stretch (too much vested interest by the LED mfgrs. to exaggerate the problem), but still the delay is undoubtedly statistically significant in rear-end accidents even thought a 100mS (1/10 sec) delay is almost not perceptible except in side-by-side comparisons (i.e., incandescent immediately beside an LED turned on by the same switch).

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

The figure came from a table in the databook of a manufacturer of incandescent lamps.

Reply to
Daniel J. Stern

| > ...Still, I wish Chrysler had used LEDs for this application, particularly for | > the quicker illumination... | | That's the second time you mentioned the LED being quicker. While it is | indeed quicker, I don't think that is significant in reaction time. An | incandescent takes, what, 20 or 30 mS to light up? That's kind of like | saying that the reason you have to protect your skin more from the sun | in Denver is because you're a mile closer to the sun than you would be | at sea level (92,999,999 vs. 93,000,000 miles). 8^) (BTW, you do have | to protect your skin more in Denver, but not for that reason - just | thought I'd say that too before someone misunderstood and felt compelled | to point that out.) | | Bill Putney | (to reply by e-mail, replace the last letter of the alphabet in my | address with "x") | | |

Reply to
James C. Reeves

OK. So where do companies like GE and Sylvania/Osram hide their technical data sheets - all I can find by drilling down into their web sites are gross characteristics. I'd be interested in seeing the full engineering data sheet on, say the 921 and 912 CHMSL lamps used on LH vehicles. I'd also be interested in seeing where (on the time scale after application of voltage) these bulbs are up to, say, 70, 80, 90% of full brightness.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

Yeah, James - that's pretty much what the Agilant (same as Hewlett Packard) article

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I linked in my other post said. The delay is probably notsignificant on small sample basis (the variation in reaction timesbetween drivers and with the same driver from one day to the next isprobably larger than that), but over thousands of accidents and nearaccidents, I'm sure there is a statistical significance. Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

The datasheet for an automotive bulb does not contain information on rise time. Given proper power supply, rise time is so similar for all automotive miniature lamps that there's no point.

That said, this kind of info is not found on the websites, which are aimed at consumers and knownothing MBAs. Sylvania publishes a miniature lamp application and dataguide that was still free for the asking last time I checked.

General Electric has this to say on page 21 of their 2004 Transportation and Miniature Lamp Catalogue: "The rate of rise and decay time depends on the mass of the filament to be heated. In general, the incandescence (rise time) to 90% intensity is about 100 to 300 milliseconds, and the nigrescence (decay time) is about 40 to 100 milliseconds. These values vary somewhat with each lamp type. The times are directly related to the lamp current; therefore, low-current lamps have the fastest response times."

DS

Reply to
Daniel J. Stern

| > I've read that the difference between the two is 200ms. At highway speeds I | > believe it's close to a car length travel distance. I suppose that extra

200MS | > could make a difference in a few cases to avoid a accident. | | Yeah, James - that's pretty much what the Agilant (same as Hewlett | Packard) article |
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| that I linked in my other post said. The delay is probably not | significant on small sample basis (the variation in reaction times | between drivers and with the same driver from one day to the next is | probably larger than that), but over thousands of accidents and near | accidents, I'm sure there is a statistical significance. | | Bill Putney | (to reply by e-mail, replace the last letter of the alphabet in my | address with "x") | | |
Reply to
James C. Reeves

Interesting. The Intrepid and 300M have the bulbs in the trunk lids. The Concorde (which I have) has it in the back shelf behind the rear seat (visible in the rear window). That explains why I've only had one of the two bulbs go out in 3 years of ownership. You could get an aftermarket kit to remount in the rear window (and I understand wanting to find a different solution - hmmm - I wonder if a rear deck and CHMSL from a Concorde would fit an Intrepid - probably wishful thinking, and also not an easy fix). Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

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, halfway down. Hella makes nice LED units in New Zealand but doesn't import them to North America.

DS

Reply to
Daniel J. Stern

That's as opposed to MBA's who know a lot? It could happen!! 8^)

I'm convinced - thanks for the info.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

So, Daniel, does that thing run on AAA's or AA's, and how often do the batteries need to be replaced? 8^)

Seriously - looks like a well-made product. Might be worth considering, eh, Greg?

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

Naw, AA batteries are envire-mentally unsound, so it's powered by a miniaturized squirrel running inside a miniaturized squirrel wheel.

Way better than the crap that flooded the US market when center brake lights first started coming on new cars.

DS

Reply to
Daniel J. Stern

I doubt that the delay has anything whatsoever to do with it.

I think it's much more likely that the attention-grabbing factor is simply because the LED lamps illuminate differently than incandescent lamps, people have 5 million years of evolution that has programmed them into paying attention to anything in their field of vision that is new or different than ordinary.

Once everyone has one, and you see the things on the ass-end of everything from New Bugs to crackerboxes going down the road, they will be no more effective than the incandescent lights that they are replacing, as the average drivers will then lapse back into their normal comas.

Ted

Reply to
Ted Mittelstaedt

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