Intrepid High Mount Stop Lamp LEDs?

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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? 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.
 
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?
Click to expand...

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.
 
Daniel J. Stern said:
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.
Click to expand...

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.
 
|
|
| "Daniel J. Stern" wrote:
|
| > On Sat, 21 Feb 2004, Greg Houston wrote:
| >
| > > 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).
 
Greg said:
...Still, I wish Chrysler had used LEDs for this application, particularly for
the quicker illumination...
Click to expand...

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")
 
Bill said:
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.)
Click to expand...

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. :)
 
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.
Click to expand...

It certainly is.
incandescent takes, what, 20 or 30 mS to light up?
Click to expand...

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


DS
 
Daniel J. Stern said:
It certainly is.


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

DS
Click to expand...

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):
http://www.agilent.com/about/newsroom/features/gettoknow/030102electronics.pdf

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")
 
The 200mS is probably a stretch (too much vested interest by the LED
mfgrs. to exaggerate the problem)
Click to expand...

The figure came from a table in the databook of a manufacturer of
incandescent lamps.
 
|
|
| Greg Houston wrote:
| >
| > ...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")
|
|
|
|
|

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.
 
Daniel J. Stern said:
The figure came from a table in the databook of a manufacturer of
incandescent lamps.
Click to expand...

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")
 
James C. Reeves said:
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.
Click to expand...

Yeah, James - that's pretty much what the Agilant (same as Hewlett
Packard) article
(http://www.agilent.com/about/newsroom/features/gettoknow/030102electronics.pdf)
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")
 
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.
Click to expand...

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.
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.
Click to expand...

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
 
|
|
| "James C. Reeves" wrote:
| >
| > 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
|
(http://www.agilent.com/about/newsroom/features/gettoknow/030102electronics.pdf
)
| 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")
|
|
|
|
|

Thanks for the link..
 
Greg said:
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. :)
Click to expand...

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")
 
Daniel J. Stern said:
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...
Click to expand...


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

... 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
Click to expand...

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")
 
Daniel J. Stern said:
http://www.danielsternlighting.com/products/products.html , halfway down.

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

DS
Click to expand...

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

Naw, AA batteries are envire-mentally unsound, so it's powered by a
miniaturized squirrel running inside a miniaturized squirrel wheel.
Seriously - looks like a well-made product.
Click to expand...

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

DS
 
Bill Putney said:
probably larger than that), but over thousands of accidents and near
accidents, I'm sure there is a statistical significance.
Click to expand...

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
 
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