Interesting Pacifica feature

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.

 

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.

 

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 ()

 

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 ()

 

Then I guess Volvo is wasting its time:

http://conceptlabvolvo.com/us/scc/

(Click on number 5, then select "making brake lights brainier").

 

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:
http://www.lumileds.com/pdfs/DS46.PDF.

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 www.lrc.rpi.edu.
Click on NLPIP and then search for the publication.

 

This product you mention is an oddball high-power blue LED, and is NOT
representative of "regular" LEDs.

 

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:

http://www.lrc.rpi.edu/programs/solidstate/completedProjects.asp?ID=51

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
dimmer.

 

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.




Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/
Aurora, Ontario

 

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.

 

On 7 Jan 2004 22:47:16 -0500, (John D.
Bullough, Gurley Building) wrote:

[snip]

[snip]

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.

 

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.

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")