Energy & Sustainability Science Technology
LED traffic lights don’t melt snow
450px-Modern_British_LED_Traffic_Light.jpg

Interesting story on MSNBC about how the newer energy-efficient LED traffic lights are causing accidents because, unlike conventional incandescent traffic lights, they do not generate enough heat to keep themselves clear of snow, and thus can easily become obscured by it. I don’t think anyone’s saying LED traffic lights are a bad idea in general, but it is an interesting parable about thinking all the way through a problem from a design perspective. [Thanks, Ron!]

42 thoughts on “LED traffic lights don’t melt snow

    1. Coming from a place where there’s no snow, this never even occurred to me.

      Though, I have to say…for the low burnout/failure rate of LEDs, there are WAY too many broken lights in my area. I’m shocked at how many single LEDs are dark in the stoplights around here. Often multiple LEDs in one “bulb”, so I’m inclined to believe it’s an issue with the bulb construction, not the LED batches. Three cheers to the lowest bidder!

  1. I live in Canada, and we get the whole range – some wicked cold, snowy days (even as low as -40 for a day or two a year isn’t unusual) and wet, sticky slop. We also have LED stop lights everywhere.

    I have never seen this problem, or even noticed any partially obscured lights.

    And even if lights do become obscured, the only reason they’d cause accidents is if two moron met at the same intersection. If you can’t see the lights, or they’re not working, it just becomes a four-way stop.

    Oh, and as for the LED headlights not used in cars – they’re only now becoming bright enough with reliability (ultra-bright LEDS can overhead and have a very short life). Most new cars have set-back headlights with plastic covers. That design isn’t melting the snow off with heat, either.

    1. It’s possible that only one or two sides of a signal could become obscured (from wind blown snow, for example). Drivers approaching the obscured signal may treat the intersection as a 4 way stop, but drivers approaching the clear side of the signal would not. This could lead to some dangerous interactions.

  2. They have dealt with this before. In the 70’s and 80’s they switched out vacuum tubes for solid state electronics inside the traffic light control boxes. Turns out the heat from the tubes were keeping the capacitors form absorbing too much moister. So they had to go back in later and swap the caps.

    In this case it seems to be an easy fix with a simple circuit and some heat tape.

    1. Electric cars are generally equipped with electric heaters, which provide simple, reliable heat at the expense of some range.

    2. Back in the early 90s I worked as a technician for a company in the UK doing electric car controllers. The electronics were all mounted on an aluminium back plate that had to have water cooling. They were using big IGBTs for the switching I seem to recall.

      Once we worked on a Pivco car (little Norwegian thing that later on became the Think) and that also had a water cooled motor. We had to have a small electric pump to circulate the cooling water but we had it wired to a toggle switch so you could turn it off since it made a horrible racket in an otherwise silent car. I used to think of that as the ‘stealth mode’ switch.

      I don’t know how far electric car design has progressed now but I imagine where you have big currents and lots of power moving about there will be heat in the system somewhere that can maybe be tapped for passenger compartent heating?

  3. I read about an alternate solution on another blog, see below, shortened for content.

    There is an easy and cost effective solution to this problem that is fast and uncomplicated… The solution is a scoop visor, available through McCain Inc. (www.mccain-inc.com/traffic/item/signals/signal-visors.html). The scoop visor is specifically designed to help reduce snow deposits and build up on the face of LED traffic signals.

    1. Snow accumulates on top of the shades. Traffic lights have shades because the sun, shining straight onto the colored lenses and reflecting off the internal reflector could make it look like all three lights were on at the same time. LED traffic lights do not do that, as the LED casings are clear and there is no reflector. Sunlight hitting them straight on makes them look no different: you only see the light which is on.

      No need for shades in LED traffic lights. No place for the snow to accumulate.

      Simplest of all solutions: yank the shades.

  4. I’ve seen that problem here in Colorado a few times in the last couple of years. It generally happens when we get sustained blowing snow that collects in the lights. All of the lights here appear to have shades with openings at the bottom, but with the right combination of temperature and moderately wet snow, it will collect and stick to the lamp despite the opening.

  5. A good example of why our representatives should think twice (and then three times) before banning things for our own supposed good.

  6. I never really thought of LED lights as power saving for traffic lights, which is what everyone is saying thats the reason that they were installed. The reason i like them is that they seem to work forever and are very visable in daytime conditions unlike alot of the older style lights. (ive almost gone through red lights because of glare and dim lighting makeing it next to impossible to tell what color the lights are)

  7. This came up in the NPR Car Talk show’s Puzzler segment a long time ago, maybe a year. It really is something you’d only key into in the Northern hemisphere, and there it’s not even an issue everywhere. Certainly, though, where we’re looking for solutions to make energy saving more cost efficient in the global south, these sorts of alternatives (fewer bulbs dying and wasted, less energy consumed) may have their applications in some places.

  8. Oh my god, I’m tired of hearing about this. treehugger does an article, and every other website (even gadget sites) starts discussions on it. Incadescent lights do not provide enough warmth to melt snow if it drops below a certain temperature, and the cost savings from LED’s could easily power a heater if the temperature drops below a certain temperature (your not talking about a lot of volume inside a stoplight). Also, accidents are blamed on blocked stoplights maybe every few years, a very small percentage compared to other causes of accidents. If people weren’t idiots and used caution when lights were obscured, it wouldn’t be an issue to begin with.

    1. I had no idea there’d been an article on Treehugger. I got the lead from a personal e-mail from my friend Ron (which is why I thanked him). He linked me to a summary of a news item on NPR, which credited the Associated Press. Then I Googled it and found MSNBC seemed to have the most detailed coverage, so I linked there.

      As I said, I don’t think anyone is going to argue (I’m certainly not) that LED stoplights are a bad idea. The MSNBC article has quotes to the effect that the power savings of the LED lights more than make up for the cost even of having crews come out and manually clean out the snow.

  9. In my hometown the lights being switched (first) to LED are the ones facing East and West, which early morning/late afternoon are hit straight-on by the sun. The idea is not save energy, but to make the lights more visible.

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I am a long-time contributor to MAKE magazine and makezine.com. My work has also appeared in ReadyMade, c't – Magazin für Computertechnik, and The Wall Street Journal.

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