LED traffic light puzzler on NPRadio show..

[Diesel_Bomber]

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.

:buddies:

 

[Flying Turtle]

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

 

[Steve K]

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.

 

[Avatar28]

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.

 

[Avatar28]

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

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.

 

[scott.cr]

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.

 

[JimmyM]

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

 

[Darell]

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!

 

[Cyclops942]

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?

 

[Avatar28]

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.

 

[scott.cr]

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.

When a mechanical traffic light switch changes the lights, there is about a 1/10 second period where none of the lights receive power. With incans, the filament is still "dimming down" on one light by the time the next one is lit. The switches were designed with this in mind so you don't have two lights simultaneously lit.

Since LEDs turn off instantly, now you have that 1/10 second where NO lights are lit.

A few years ago this was a reason my city only used LEDs for one of the three colored lights. These days, I imagine this problem (if you want to call it a problem) has probably been rectified with some sort of internal circuitry to compensate.

 

[LukeA]

Since LEDs turn off instantly, now you have that 1/10 second where NO lights are lit.

But it's only 1/10 second. That's not enough time for anything begin to happen before the other light comes on.

 

[eluminator]

The new fangled headlights they put on cars these days suffer from the "no heat" problem. When the road is covered with slush, I've had it build up on my headlights 1.5 inches thick. This made the headlights worthless. This didn't happen with the old sealed beam headlights. They were hot and the slush didn't stick.

 

[Avatar28]

The new fangled headlights they put on cars these days suffer from the "no heat" problem. When the road is covered with slush, I've had it build up on my headlights 1.5 inches thick. This made the headlights worthless. This didn't happen with the old sealed beam headlights. They were hot and the slush didn't stick.

Maybe that's why some of those fancy cars have wipers on their headlights.

 

[eluminator]

Maybe that's why some of those fancy cars have wipers on their headlights.

And I suppose those wiper blades are heated to prevent them from icing up.

So it looks like we need fancy traffic lights with wipers. And we will have to employ a lot of people to change the wiper blades occasionally.

 

[UncleFester]

Yeah that one tenth a a second is a real problem.. No one would know what to during that time when no lights are on.

 

[PhotonWrangler]

I've seen this symptom also. It is a little disconcerting, and it inistantly identifies the controller as one of the mechanical ones (that and the clunketly-clunk that emanates from the cabinet). All of the controllers I've seen recently are the electronic ones.

There's a huge benefit from switching to electrronic controllers; it makes it much easier to coordinate the lights along a stretch of road.

 

[TedTheLed]

just a note to confirm that the lack of heat was indeed the answer to the puzzler this morning on Cartalk..congratulations all you winners out there :thumbsup:

 

[65535]

The problems I see are in foggy conditions you would have a hard time seeing LED light. As for the 1/10th of a second off time they could easily add a capacitor to each LED bank that would store just enough energy to run the LEDs for 1/8th of a second or so while the contacts switched LED bank for each color. With enough available current the Caps would charge almost instantly anyways.

 

[WNG]

The problems I see are in foggy conditions you would have a hard time seeing LED light.

Why do you claim this? I can't deduce a reason. Please explain.

IMHO, I see no performance reduction for poor weather such as fog. Actually performance should improve. Given that such lights use red-orange and green spectrum LED arrays. All the power output is constrained to the desired color spectrum, not through a color filter.

A nice example of LED improvement is the use of red LED tail light strobe on Formula 1 cars. Compared to the old incan bulb and red lens of decades past, the LED units are more visible in the mist and spray of a wet race.