Look at a traffic light next time you're near one. Increasingly they are LED. The colour stability on traffic lights is very carefully controlled. Same with large displays such as motorway matrix signs, imagine what a PITA it was when they were incandescent bulbs.
Actually, for white LEDs at full power 50K hours is the high end of claims not easily "shot down". White LEDs have a problem with phosphor deterioration, which is not a problem with colored LEDs.
As for actual life expectancy of white LEDs - I have heard enough figures anywhere from 6K to 50K hours for good ones! Less if you push them or do not keep them cool!
- Don Klipstein ( snipped-for-privacy@misty.com)
Traffic signals are especially favorable to LEDs, since most LEDs specialize in producing colored light while incandescent lamps can have about 2/3 or a bit more of their output removed by filtering to appropriate shades of red or green. Also, please consider that traffic signal incandescents are less efficient than usual household incandescents due to compromise for designing for long life expectancy and vibration resistance. Furthermore, LEDs, especially with add-on optics, can more easily than traditional incandescent-related optics be tailored to waste less light by shining less light into directions where the requirement is less or nonexistent.
This should account for why red and green traffic signals were able to acheive energy savings of 90% (or slightly less) even when white LEDs had luminous efficacy hardly exceeding that of 100 watt 750 hour 120V household lightbulbs. And please note that it is recent news for available (maybe available soon) white LEDs to do much better than that, and still have luminous efficacy below that of most compact fluorescents.
Some details in:
Although Don, note that they have been LV halogens for at least last 20 years in the UK, often with programmed current drivers, and not mains lamps like in the US.
No they are not. The wavelengths produced by red, green and yellow LEDs are incorrect for use in traffic signals, and the colpour shifts encountered in these LEDs made their use extremely difficult to implement. It is only (relatively) recently that the problems have been overcome.
Hell, what would I know, eh?
I'd not argue, but I think they are comming on, and we won't have to wait too long to see them breaking into the market in more general applications. Wait & see...
From what I hear about led traffic lights: a) the amber & green colors are incorrect and (particularly the ambers) drift about with temperature . b) the output falls out of spec with time. c) a) & b) are ignored.
Is this true? Does anyone measure them ?
But non of these require continuous spectrum light. LEDs are brilliant at single colour signal lights, as the efficiency is high - and they also provide a degree of directionality which might be lacking in other types without a reflector which further aides the perceived efficiency.
However, my gut feeling is that they are a *long* way off from providing a decent replacement to halogen in a domestic environment for those who want a 'pleasant' natural light.
Of course, not all care. ;-)
%steve%@malloc.co.uk (Steve Firth) wrote in news:1gsbwvr.1ihvj5hj1q0puN%%steve%@malloc.co.uk:
Having noticed that their colour isn't quite the same as 'traditional' traffic lights, I did wonder if it would be sensible to take the opportunity presented by their introduction to change their shapes as well? We are familiar with the octagonal STOP signs - so why not red octagon, amber triangle and, umm, green circle?
In message , Rod Hewitt writes
Have you noticed that the UK LED lights have a full size LED panel behind the pedestrian crossing "walking man" cut-outs. By contrast in France the LEDs form the shape of the character.
In message , R.Lewis writes
From what I _see_ of the lights around Glasgow, the red is red, the amber is amber and the green is green. They are much brighter than traditional halogen lamp versions and emit in a very controlled area as is the style of LEDs.
I like 'em.
I know that green is supposed to be a particularly bluey green to avoid colour vision problems, but is this really apparent with the LED lights?
"Rod Hewitt" wrote | Having noticed that their colour isn't quite the same as | 'traditional' traffic lights, I did wonder if it would | be sensible to take the opportunity presented by their | introduction to change their shapes as well? | We are familiar with the octagonal STOP signs - so why | not red octagon, amber triangle and, umm, green circle?
Using LEDs you could have a little animated car chugging on the green. Would be great for pedestrian crossings -- a stationary red man could change to an animated walking green man.
Owain
Partially. When LED traffic signals were in their infancy the specs were all written around incandescents and so didn't address characteristics particular to LEDs such as intensity and color drift over time. The Institute of Traffic Engineers (ITE) just released a Draft of a proposed spec (although it may now be final) for LED Traffic Signal Heads for US roads. I don't know what's in effect for Europe, etc.
As for existing LED traffic heads - a number of them are color-compliant, but there are also a number that are close but do not fall within the established color parameters (and some that are nowhere near close). My opinion is that the purchasing agencies ignored or were not aware of the lack of compliance and went ahead because of the energy and maintenance savings.
My company does as a compliance laboratory. We could (but don't) measure them in the field. It's VERY expensive.
Europe doesn't have the glaring-green problem we've got in North America, 'cause their LED traffic signals have variable intensity that dims and brightens with ambient light conditions. I'll be very surprised if any glare-control measures at all made it into the ITE spec; glare is generally ignored (dismissed as a non-problem) in North America.
DS
Just like global warming and the lack of WMD. (Our politicians got the last bit wrong too!)
You are kidding? Please tell me you are...
(Is this "Big" Clive of the "Bam "Board" & the "Electrocutioner"
New spec has maximum permissible luminous intensity not to exceed three times the minimum required peak intensity. Also allows the option of nighttime dimming so long as it does not drop below 30% the minimum maintained luminous intensity (in other words, can be variably dimmed dependent on ambient light). Also, luminance across the entire lens must be uniform, not exceeding a max to min ratio of 10 to 1.
So glare is not ignored - it just wasn't considered previously because when it was just incandescent traffic signals no one was going to make their lamps too bright due to heat and energy cost issues. It just takes longer for the specs to catch up. Now that there's a specification in place, it's up to the municipalities to make sure their existing stock and/or new stock meet the published requirements.
In message , Andrew Chesters writes
Yes here in Glasgow they use a generic LED illumination panel and just mask off the unwanted LEDs. Seems a bit wasteful to me, but obviously it keeps the PCB count low. One PCB does all the graphic stuff like walking-men and arrows.
In message , Owain writes
Likewise you could replace the red "don't walk" man with the green "walk" man being hit by a yellow car with animated LED blood spray.
Always liked the East German Ampelmann, but Belgium has a particulary swinging illustration as well:
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