LED traffic light puzzler on NPRadio show..

TedTheLed

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I just finished listening to "Car Talk" on National Public Radio (on Sirius satellite) and this week's riddle is, basically, "what is the problem with these new LED traffic lights" ?

The Tappet bros. touched on all the advantages of LED traffic lights; though the initial cost and installation is expensive, they are cheaper to run in the long run due to extended lifetime and lower energy consumption, they are brighter than incans, and even if a few LEDs do burn out the traffic light still functions, unlike the incan..all seemingly a win/win situatin -- yet the question remains; what is the one drawback or problem with LED traffic lights when compared with incans?
 

geepondy

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Are they any better/worse then incandescents in bright light? Sometimes, particularly during a part of day when the sun is shining on the light, it's difficult to distinguish whether the red or green is on. I wonder if LEDs offer any improvement in this area. I would guess not.

Also are they true red/green/orange LEDs or are they white LEDs with colored filters?
 

TedTheLed

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sounds like good guesses to me gee, you may even be right.

..they'll have the answer on next week's show.. :)
 

jtr1962

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Probably due to the much lower power consumption snow on the lens won't melt off. This seems like it would be a very rare problem, perhaps only in a severe blizzard. I have yet to see snow accumulate on the lens of any local traffic lights. Ours always have a cylindrical glare shield around the light though. Maybe that helps.
 

jtr1962

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Also are they true red/green/orange LEDs or are they white LEDs with colored filters?
No, they're colored LEDs. Even with today's whites approaching 100 lm/W it is still more efficient to use colored emitters rather than white plus a filter. This is especially true with red since white LEDs don't emit much in that area.
 

greenlight

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One difference is the 'cat eye' lens effect from the incan is visible to only the oncoming drivers, while the LED lights are visible from the side, even the reflection of the light on the shroud that is supposed to make it invisible to side traffic. Maybe they should be using fewer LEDs and invest in some nice optics.
 

gadget_lover

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The problem I have with them is that they focus so well that I can clearly see red lights all across the valley as I drive down the hill into town. Some look VERY bright.

When driving at night I sometimes (when distracted) catch the light from down the block and think the light I'm sitting at has changed.

And then there are all those lost jobs. The poor guys who used to change the bulbs.

Other than that....

Daniel
 

TigerhawkT3

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Caution: :rant: ahead.

I can't stand the few remaining incan traffic lights in my neighborhood. I drive west in the late afternoon on my way home from school, and there's an intersection that has all incan lights except for one post on the corner. I always have to glance back and forth between the intersection and the LED traffic light, because the incan ones don't even look like they're on until I'm in the middle of the intersection.
 

Diesel_Bomber

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I don't understand why it matters if a traffic light is visible from other angles, other than it being inefficient?

On the light tree for drag racing, LED bulbs sure screwed up the timing and gave a lot of people false starts, due to LED's coming up to full brightness so much faster than an incan bulb. I don't know how this has anything to do with a stoplight, though. Maybe employees in charge of replacing stop light bulbs had to be let go, due to lack of work?

I'm interested in what the disadvantage turns out to be. :buddies:

Edit: Oops, looks like Gadget Lover beat me to the jobs thing.
 
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WNG

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I'm with JTR1962 on this one, lack of forward radiated heat to keep them clear of ice and snow accumulation. The show is based out of New England afterall.
 

LukeA

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Are they any better/worse then incandescents in bright light? Sometimes, particularly during a part of day when the sun is shining on the light, it's difficult to distinguish whether the red or green is on. I wonder if LEDs offer any improvement in this area. I would guess not.

Also are they true red/green/orange LEDs or are they white LEDs with colored filters?

It's fairly easy to tell if the LED traffic light is red, yellow, or green. They are brighter than most other traffic lights and the off sections are black and not simply less-colored versions of their "on" color.

There's no logical reason to use white LEDs with filters and, from what I can see, the LEDs are exposed and not behind any kind of filter. I've also seen that the shrouds don't have bottoms and won't accumulate snow.
 

Norm

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Are they any better/worse then incandescents in bright light? Sometimes, particularly during a part of day when the sun is shining on the light, it's difficult to distinguish whether the red or green is on.
Even incans suffer this problem
Norm
 
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PhotonWrangler

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Probably due to the much lower power consumption snow on the lens won't melt off. This seems like it would be a very rare problem, perhaps only in a severe blizzard. I have yet to see snow accumulate on the lens of any local traffic lights. Ours always have a cylindrical glare shield around the light though. Maybe that helps.

JTR, I was going to say this also. It's fairly rare that bulb heat is needed to melt off the snow and ice, but when it IS needed, it's an absolutely critical safety issue.
 

LukeA

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JTR, I was going to say this also. It's fairly rare that bulb heat is needed to melt off the snow and ice, but when it IS needed, it's an absolutely critical safety issue.

But if it's ice, especially frozen-freezing-rain ice, then isn't it pretty clear? And if the conditions are so bad that the light is totally obscured, why can't you just treat it like a 4-way stop (like you do when the power goes out)?
 

PhotonWrangler

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But if it's ice, especially frozen-freezing-rain ice, then isn't it pretty clear? And if the conditions are so bad that the light is totally obscured, why can't you just treat it like a 4-way stop (like you do when the power goes out)?

Yes, if it's just a sheet of ice, it's fairly transparent, however it's more likely to be obscured by snow in certain climates. And most rational people know to treat a traffic light outage as a four-way stop... however... :tinfoil:
 

CanadianGuy

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Probably due to the much lower power consumption snow on the lens won't melt off. This seems like it would be a very rare problem, perhaps only in a severe blizzard. I have yet to see snow accumulate on the lens of any local traffic lights. Ours always have a cylindrical glare shield around the light though. Maybe that helps.

Heheh, We get that quite often here in certain parts of Canada. I live in the prairies, and during winter we get blowing snow like crazy.

I see this phenomenon more on buses with LED brake lights, compared to traffic lights, but I think I have seen it.

That would be funny if they had to put a heater on the lens, but of course that would be silly because it would negate any benefit to energy savings.
 

jtr1962

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That would be funny if they had to put a heater on the lens, but of course that would be silly because it would negate any benefit to energy savings.
It's very easy to make a heater which only runs when needed to keep the lens temperature above freezing. This would still allow the energy saving benefits of LEDs most of the time.
 

TedTheLed

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I listened to the show again today, and have an additional clue;

they said something to the effect that 'some of our listeners would have an additinal clue to the puzzle 'a couple of months from now...'

this definitely sounds to me like snow in New England.

I think the problem could be pretty easily solved by some sort of thin easily heated surface over the LEDs; when the snow blocks the light the surface would have to heat just enough to break the bond of any accumulated ice/snow and allow it to slide down and off in a matter of seconds..just like I defrost my fridge; instead of melting all the ice off, I just turn off the fridge and let the surfaces heat just enough so I can easily slide big slabs of ice off and out..
 
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