Intrepid High Mount Stop Lamp LEDs?

Discussion in 'General Motoring' started by Greg Houston, Feb 21, 2004.

  1. Greg Houston

    Greg Houston Guest

    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.
     
    Greg Houston, Feb 21, 2004
    #1
  2. 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, Feb 21, 2004
    #2
  3. Greg Houston

    Greg Houston Guest

    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.
     
    Greg Houston, Feb 22, 2004
    #3
  4. |
    |
    | "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).
     
    James C. Reeves, Feb 23, 2004
    #4
  5. Greg Houston

    Bill Putney Guest

    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 Putney, Feb 23, 2004
    #5
  6. Greg Houston

    Greg Houston Guest

    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. :)
     
    Greg Houston, Feb 23, 2004
    #6
  7. It certainly is.
    200mS to full intensity, vs. >2mS to full intensity for an LED. Do the
    math.


    DS
     
    Daniel J. Stern, Feb 23, 2004
    #7
  8. Greg Houston

    Bill Putney Guest

    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")
     
    Bill Putney, Feb 23, 2004
    #8
  9. The figure came from a table in the databook of a manufacturer of
    incandescent lamps.
     
    Daniel J. Stern, Feb 23, 2004
    #9
  10. |
    |
    | 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.
     
    James C. Reeves, Feb 23, 2004
    #10
  11. Greg Houston

    Bill Putney Guest

    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")
     
    Bill Putney, Feb 24, 2004
    #11
  12. Greg Houston

    Bill Putney Guest

    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")
     
    Bill Putney, Feb 24, 2004
    #12
  13. 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
     
    Daniel J. Stern, Feb 24, 2004
    #13
  14. |
    |
    | "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..
     
    James C. Reeves, Feb 24, 2004
    #14
  15. Greg Houston

    Bill Putney Guest

    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")
     
    Bill Putney, Feb 24, 2004
    #15
  16. Daniel J. Stern, Feb 24, 2004
    #16
  17. Greg Houston

    Bill Putney Guest


    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")
     
    Bill Putney, Feb 24, 2004
    #17
  18. Greg Houston

    Bill Putney Guest

    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")
     
    Bill Putney, Feb 24, 2004
    #18
  19. 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
     
    Daniel J. Stern, Feb 24, 2004
    #19
  20. 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
     
    Ted Mittelstaedt, Feb 24, 2004
    #20
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