Interesting Pacifica feature

Discussion in 'Pacifica' started by Art Begun, Dec 31, 2003.

  1. Much less. Nichia developed the first high brightness (1cd) blue LED
    in 1993. I don't have a date when they were commercially available but
    it must have been at least a couple of years after that.
    Victor Roberts, Jan 7, 2004
  2. Art Begun

    Aardwolf Guest

    Which as it turns out are Whelen LFL all-LED bars, if anyone wants to know. They do
    seem to have red and blue outer covers though, I'm not sure what that does to the color
    or brightness of the LED modules in question. Though from what I can estimate, based
    on the photos I've seen, probably not too much. (A blue filter tends not to block blue
    light after all, or red => red, etc.)

    Aardwolf, Jan 7, 2004
  3. Art Begun

    Aardwolf Guest

    Good point. I guess the MSP agrees with that basic beacon requirement too (on their
    cruisers, that is, not forklifts). And AFAIC in those roles either are better than

    Aardwolf, Jan 7, 2004
  4. Art Begun

    Bill Putney Guest

    Heh heh! I think you're right on that. I was working from memory, and
    originally typed in "ten years", but changed it to fifteen just before
    hitting send to be on the safe side. I'm busted! 8^)

    To find out, we could check the old Digi-Key catalogs, eh? 8^)

    Bill Putney
    (to reply by e-mail, replace the last letter of the alphabet in my
    address with "x")
    Bill Putney, Jan 7, 2004
  5. I can tell you that Philadelphia has had LED for most of its red traffic
    signals for something like 4-5 years with nearly all appearing nearly
    enough full-blast.
    Green LED traffic signals have seen some use for a couple years already
    in some of Philadelphia's suburbs with no noticeable color change, and not
    yet much of a brightness degration that would actually be welcomed by
    Yellow sees less use because it has much less on-time and therefore less
    energy savings. Yellow would also degrade slower than red or green. Most
    "usual" traffic signals that I see spend something like 50% of the time
    red, 45% green (give-or-take in the case of intersections between streets
    that greatly differ in traffic volume) and something like 5% of the time
    Yellow LED traffic signals also consume more power than red and green
    ones of similar quality and same time of manufacture, since yellow LEDs
    tend to have slightly less luminous efficacy than red and green ones while
    there is demand to be brighter than red and green the way yellow
    incandescent traffic signals are.

    - Don Klipstein ()
    Don Klipstein, Jan 7, 2004
  6. It was only a year or two, as far as I remember. Another thing:
    Gallium nitride blue LEDs (presumably at least moderately high brightness)
    have been made as laboratory prototypes, if I remember correctly, as far
    back as the mid 1980's. But these tended to self-destruct or degrade
    unacceptably rapidly in use. What Nichia did was develop a blue LED that
    avoided the rapid degration / self-destruction of earlier gallium nitride
    Cree had a low brightness blue LED in production in the early 1990's.

    - Don Klipstein ()
    Don Klipstein, Jan 7, 2004
  7. Then I guess Volvo is wasting its time:

    (Click on number 5, then select "making brake lights brainier").
    Scott in Aztlán, Jan 7, 2004
  8. What makes you say so? Virtually every automaker -- and a great many other
    parties besides -- engage in research on devices that are not legal under
    prevailing regulations in whatever country you care to name. It's not a
    waste of time, but the way in which safety systems evolve. Flashing CHMSLs
    have been found incompatible with present-day North American rear lighting
    systems, but that's not the end of the discussion; perhaps Volvo or some
    other group will come up with an entirely novel signalling system that's
    better than anything extant in any country.

    And besides, flashing CHMSLs are still being examined outside North
    America where there are not yet any flashing red lights on the backs of
    cars, leaving that modality open for new assignment.

    Daniel Stern Lighting, Jan 7, 2004
  9. Art Begun

    Steve Guest

    This is quite contrary to my experience both as a consumer of commercial
    LED products as an EE working periodically with LEDS for the last 20
    years. Even as the technology has changed drastically (when I started my
    career, both white and blue LEDS were 'an impossibility') I have never
    seen such behavior in anything except early development LEDs and
    severely over-driven LEDs.
    Steve, Jan 7, 2004
  10. Art Begun

    Steve Guest

    That's where technology was when I entered the professional world. The
    blue prototypes would quickly turn to a sick sort of green color, work
    for a somewhat longer period that way, and then fail.

    I would guess that it was about 1995 when some of our guys started using
    blue LEDs as indicators (not normally visible to the operator, deep down
    in card cages) in equipment, more for the novelty than anything else.
    They're still working.
    Steve, Jan 7, 2004
  11. I am not clear which part is contrary to your experience. The fact
    that most LEDs will operate virtually forever or the fact that their
    output will decrease with time?

    Regarding the decrease in light output from LEDs over time, have you
    made any long term measurements of the efficacy of LEDs or are you
    relying on informal observations made with your eyes? My comment is
    based on data published by LED manufacturers, such as Lumileds, and
    data measured under controlled conditions at independent laboratories
    such as the Lighting Research Center.

    You can find a statement about LED lumen depreciation (but no graph)
    on page 6 of the document at the following link:

    You can find lumen depreciation curves for red, green, blue and white
    LEDs in report "LED Lighting Systems", NLPIP Lighting Answers, Volume
    7, Issue 3, May 2003. This report is available at
    Click on NLPIP and then search for the publication.
    Victor Roberts, Jan 7, 2004
  12. Art Begun

    dizzy Guest

    This product you mention is an oddball high-power blue LED, and is NOT
    representative of "regular" LEDs.
    dizzy, Jan 8, 2004
  13. You can find a statement about LED lumen depreciation (but no graph)
    That "oddball" high-power LED is representative of the type of LED device
    used in most illumination grade "white" LEDs, which use the blue
    emitters along with phosphors to create white light, so I am not sure
    it's so "odd."

    Not sure what a "regular" LED is, but there are a couple of graphs for
    various colored indicator-type LEDs (the familiar "chiclet" looking
    devices) as well as white LEDs of two different configurations at:

    Undoubtedly, some colors and configurations perform better in terms
    of lumen depreciation than others, but without exception they all
    reduce in output over time. While it is theoretically possible using
    fancy driving circuits to maintain constant light output for some
    time by underdriving LEDs early in life and overdriving them later,
    this can only be sustained for so long before the amount of overdriving
    would exceed "normal" limits and probably cause the device to fail
    altogether. But holding everything constant, yes, they will grow
    John D. Bullough, Gurley Building, Jan 8, 2004
  14. Art Begun

    Boris Mohar Guest

    On Fri, 2 Jan 2004 23:47:45 -0000, "R.Lewis" <h.lewis-not this
    So, you are saying that the poorest LED arrays do not have thermal problems
    whatever they may be?
    Why not?
    LED are subject of vagaries of time? Please expand on this.


    Boris Mohar

    Got Knock? - see:
    Viatrack Printed Circuit Designs
    Aurora, Ontario
    Boris Mohar, Jan 8, 2004
  15. I pasted a link to one Lumileds LED. The same statement is included in
    virtually all the Lumileds data sheets, and older Lumileds data sheets
    had lumen maintenance curves. I urge you to take a look at the other
    data available on the Lumileds site.
    Victor Roberts, Jan 8, 2004
  16. On 7 Jan 2004 22:47:16 -0500, (John D.
    Bullough, Gurley Building) wrote:


    John - I believe you were listed in the search page as the author of
    the LRC report I cited in my message. However, the PDF copy sent to
    me by the NLPIP bot does not list any author, so I did not list an
    author in my message. If you are indeed the author of that report, I
    apologize for the omission.
    Victor Roberts, Jan 8, 2004
  17. Art Begun

    clare Guest

    I had the"opportunity" to follow a fire truck yesterday - a brand new
    pumper recently aquired by our municipality, and it has LED rear
    lights. The brake lights "strobe" 3 or 4 times before coming on
    steady. It really catches your attention.
    clare , Jan 8, 2004
  18. Art Begun

    R.Lewis Guest

    Badly expressed by me - by poorest I meant lowest light output.
    Thermal dissipation is generally not a problem when running at a total of

    Dunno why it should be- but thankfully it ain't. Its just the way it is.
    They do not last forever.
    They just gets inexorably dimmer as time passes.
    Seek the manufacturers data for effects of time and temperature on colour
    and efficacy for more detail.
    R.Lewis, Jan 8, 2004
  19. John - I believe you were listed in the search page as the author of
    Vic - no apology necessary - I consider "NLPIP" the author of all
    of those reports. I was more or less a technical writer for that
    particular report; the data comes from a number of sources cited
    in the text, including others at the LRC. I think I am listed, though,
    on p. 21, along with the others who made technical contributions.

    John D. Bullough, Gurley Building, Jan 8, 2004
  20. Art Begun

    Bill Putney Guest

    Hmmmm - 1mW is next to nothing for a *single* LED die, much less an
    array. 1mW on a single die probably would be barely visible even close
    up on a simple instrument panel - by any standard, not useful for any
    practical application, much less to be seen from a distance on
    vehicles. A single LED is typically run at 15 to 75mW depending on the
    part and application requirements. An array would be however many dies
    (LED chips) times that.

    Did you mean to type something else different than 1mW - maybe 1W for an

    Bill Putney
    (to reply by e-mail, replace the last letter of the alphabet in my
    address with "x")
    Bill Putney, Jan 8, 2004
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