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Thread: LED traffic light puzzler on NPRadio show..

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    Default LED traffic light puzzler on NPRadio show..

    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?

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    Default Re: LED traffic light puzzler on NPRadio show..

    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?
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    Default Re: LED traffic light puzzler on NPRadio show..

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

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

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    Default Re: LED traffic light puzzler on NPRadio show..

    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by geepondy View Post
    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.

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    Default Re: LED traffic light puzzler on NPRadio show..



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    Default Re: LED traffic light puzzler on NPRadio show..

    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    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....

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    Default Re: LED traffic light puzzler on NPRadio show..

    Caution: 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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    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.

    Edit: Oops, looks like Gadget Lover beat me to the jobs thing.
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    Default Re: LED traffic light puzzler on NPRadio show..

    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by geepondy View Post
    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.
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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by geepondy View Post
    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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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by jtr1962 View Post
    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by PhotonWrangler View Post
    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)?
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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by LukeA View Post
    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...

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by jtr1962 View Post
    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by CanadianGuy View Post
    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.
    Not in the summer.
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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by CanadianGuy View Post
    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.

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    Default Re: LED traffic light puzzler on NPRadio show..

    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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    Default Re: LED traffic light puzzler on NPRadio show..

    A dedicated heater would be much more durable than an incan bulb, too. Could even wire it in so that the switching circuitry is in the control box on the ground with a manual override in case the auto system fails.

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    Default Re: LED traffic light puzzler on NPRadio show..

    I heard that puzzler yesterday, too. Even with the extra clue I couldn't think of an answer. But I believe jtr1962 has nailed it. You should go to the Car Talk site and submit your answer.

    Geoff

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    Default Re: LED traffic light puzzler on NPRadio show..

    hi guys,

    I think that heat is part of the answer, but not in terms of melting snow and ice.

    I think the problem relates to the issue of retro-fitting leds into housings designed for incandescents. Incandescents love to be warm... heck, that's the only way that they work! As such, the traffic light doesn't need ventilation or heatsinks.

    On the other hand, leds don't want to be hot, but still convert most of the electrical power to heat. When you stick them into a sealed, unvented housing, they are going to get hot, which reduces their lifetime. I'm surprised that I can see failed leds in local traffic lights that are maybe 4 or 5 years old. That's a better lifetime than an incandescent, I expect, but pretty bad for a led.

    Of course, knowing Car Talk, the answer is probably about snow and Bronco Nugurski (sp?) underwear. :-)

    Steve K.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by Steve K View Post
    hi guys,

    I think that heat is part of the answer, but not in terms of melting snow and ice.

    I think the problem relates to the issue of retro-fitting leds into housings designed for incandescents. Incandescents love to be warm... heck, that's the only way that they work! As such, the traffic light doesn't need ventilation or heatsinks.

    On the other hand, leds don't want to be hot, but still convert most of the electrical power to heat. When you stick them into a sealed, unvented housing, they are going to get hot, which reduces their lifetime. I'm surprised that I can see failed leds in local traffic lights that are maybe 4 or 5 years old. That's a better lifetime than an incandescent, I expect, but pretty bad for a led.

    Of course, knowing Car Talk, the answer is probably about snow and Bronco Nugurski (sp?) underwear. :-)

    Steve K.
    Almost wonder if there might not be a way to heatsink that emitted heat out to the front of the LED to act as a heater. In any case, a heater like the rear window defroster on a car would be fine and wouldn't need to be run constantly, it could probably be run in cycles of 5-10 minutes and then off for a bit and only activated in poor weather conditions.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Here's the exact text of the puzzler from their website:

    Quote Originally Posted by Cartalk
    RAY: This is from my traffic signal series. Truth be known there was only one puzzler in the series, 'til today that is!

    You may recall the other traffic signal puzzler was about these new LED traffic lights that seem to be popping up just about everywhere. And, well, they should; they're fabulous.

    #1. They hardly ever burn out. And because every light consists of dozens of those little diodes, even if some of them do burn out, the light still works, unlike the old incandescent bulbs, which burn out and leave you with no signal whatsoever.

    More than that they use a small fraction of the energy of the old incandescent bulbs.

    And #3. They're brighter! So win, win, win, right? Wow, this is great! Now, of course, it costs quite a bit to purchase and install these lights, but in the long run they're worth it.

    However, as magnificent and wondrous and splendid as these LED lights are, they do have one disturbing shortcoming -- one flaw, one defect, if you will. What could it be?

    Now before you go off the deep end, I'm going to give a hint. If I had waited a few more months before using this puzzler some of our listeners might have found it a little too easy.
    And I did go ahead and submit that answer. Along with a bit about how LEDs actually DO emit heat, it's just down the leads instead of out the front.
    Last edited by Avatar28; 10-17-2007 at 01:03 AM.

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    Default Re: LED traffic light puzzler on NPRadio show..

    I wonder if it has something to do with that split-second "dead time" when the lights change? Some of the all-LED lights where I live switch off so fast that all lights are out before the switch contacts light up the next light.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Given the hint and the show is based in New England, it's heat. Incan traffic lights don't ice up.

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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by scott.cr View Post
    I wonder if it has something to do with that split-second "dead time" when the lights change? Some of the all-LED lights where I live switch off so fast that all lights are out before the switch contacts light up the next light.
    That isn't a "flaw" in LEDs. That's a flaw in circuit design!
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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by scott.cr View Post
    I wonder if it has something to do with that split-second "dead time" when the lights change? Some of the all-LED lights where I live switch off so fast that all lights are out before the switch contacts light up the next light.
    Why would a split-second "dead time" be a problem? And even if it were to be a problem, as Darrell points out, it's not a problem with the LEDs.

    What painfully obvious thing am I missing?
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    Default Re: LED traffic light puzzler on NPRadio show..

    Quote Originally Posted by Darell View Post
    That isn't a "flaw" in LEDs. That's a flaw in circuit design!
    Exactly. The switching is (or certainly should be) electronic. If it is going dark in between then it sounds like they never bothered to update their circuit to work properly with LEDs (which at the cost of those lights is criminal in my book). In any case I doubt that would be an issue anyways.

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