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 strobes.
--Aardwolf.
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 strobes.
--Aardwolf.
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")
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 many! 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. 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 ( snipped-for-privacy@misty.com)
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 models. Cree had a low brightness blue LED in production in the early 1990's.
- Don Klipstein ( snipped-for-privacy@misty.com)
Then I guess Volvo is wasting its time:
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.
DS
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.
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.
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:
This product you mention is an oddball high-power blue LED, and is NOT representative of "regular" LEDs.
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:
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.
Regards,
Boris Mohar
Got Knock? - see: Viatrack Printed Circuit Designs
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.
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.
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.
Badly expressed by me - by poorest I meant lowest light output. Thermal dissipation is generally not a problem when running at a total of
1mW
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.
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.
JB
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 array?
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
although I would nitpick a bit of it:
As for instrument panels - try putting 1 mW into one of the better InGaN green or blue LEDs. That's 300 microamps. Light output of a good InGaN green at 300 microamps is about that of many cheap old-fashioned GaP green LEDs at 15-20 mA.
- Don Klipstein ( snipped-for-privacy@misty.com)
My bad, I was very unclear.
My experience is that if driven at normal levels, any loss of output that would cause a noticeable reduction in the effectiveness of the signal will take YEARS. So long that many of the LEDS in the array will have begun to fail due to wire de-bonding and other failure modes.
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