LED Traffic Lights Problem - John Dunn, Consultant, Ambertec, P.E., P.C.

What price do we really pay for power efficiency?

I've heard good words said about LEDs as used in traffic lights. The LEDs are said give out as much light as the old incandescent lamps did while using less electricity to do it. So, since the LED traffic lights are power efficient, I guess they must be a great design.

On the other hand, the LEDs optical radiation pattern is quite narrow so that when viewed far enough off center, their glow can't be seen anymore.

While I was driving southbound on Route 110 in Farmingdale one very windy day, as I came to a set of LED traffic lights hanging from cables in front of the Telephonics driveway, those lights were rendered invisible from a distance by being steadily wind driven too far away from the vertical. The lights were just plain invisible until I got really, really, really close. This was a clear (no pun intended) detriment to public safety.

By comparison, the older incandescent lamps were viewable over very wide angles so that their glows would not disappear from sight like that on a windy day.

Still, the LED traffic lights are power efficient, so I guess they must be a great design unless one considers the issue of single point failures.

On another day, as I drove westbound on Sunrise Highway in Rockville Centre, I saw an entire cluster of LED traffic lights that were turning on and off, on and off, over and over again in a seemingly random fashion. At that same place the next day, the entire cluster of traffic lights had gone dark with no operation at all.

Apparently, the entire set of LED lights had been operating from a single power supply which on that occasion, had given up its ghost. The situation was nothing less than a catastrophic, single point failure, again endangering public safety.

With the old incandescent traffic lights, a single point failure would simply mean an open filament in which case, the remaining lamps would continue to function until a lamp replacement was made. With those Rockville Centre LED traffic lights, a single point failure had completely sabotaged traffic light operation at that intersection and again put public safety in jeopardy.

Still, the LED traffic lights are power efficient, so I guess they must be a great design unless one considers the issue of inclement weather.

In mid-February one recent winter, we had a blizzard. While I was driving westbound on Sunrise Highway in Wantagh, several LED traffic lights had acquired coatings of ice and snow so thick and so heavy as to hide their LEDs from view. At one light, I could just barely make out a slight little twinkle of green and at the next light a moment later, just a slight little twinkle of red. Once again, public safety was compromised over that much vaunted power efficiency.

Since the LED traffic lights are power efficient, they don't get hot enough to clear away winter ice and snow accumulations. Incandescent traffic lights however, do stay visible in the heaviest winter weather simply because they do use more power, the very trait that is held by some to be undesirable.

Still, the LED traffic lights are power efficient, so I guess they must be a great design. At least I've been told that they are.

Wait until you get to drive through a heavy snowstorm someday in a car with LED headlights.

Comments

[John Dunn]

An update:

The LED traffic lights at the Telephonics driveway were at the time made as hexagonally arranged arrays of clear lensed LEDs. I drove by there more recently and it looks like the lights are now use light diffusers to spread the viewing angle. I don't know if the light sources themselves are still LEDs or if they've been reverted to incandescent lamps, but at least the viewing angle problem seems to have been addressed.

The ice accumulation issue is still with us, however. Please see:

http://www.universalhub.com/2011/city-seeks-help-motorists-identify-ice-encrusted-t

[Cor van de Water]

Hi John,
None of the problems you encountered were due to the LED technology, only due to to bad applications of LEDs.
BTW, a single bad LED does not turn a light off, it will only
render a few of the dots dark but the entire light (normally more than hundred LEDs) continues to operate normally.
What you saw was likely the driving electronics of the light,
or the wiring had gone out. That had nothing to do with the LED light and in fact, LEDs will operate longer on a certain battery if power is lost and a LED light will gracefully degrade with failing LEDs as I described, while the incandescent light will fail completely when the filament goes out, so it is the opposite of what you complain about.
Forgetting to use a solution to remove snow is also not a problem of the LED light itself, there are many ways to get rid of snow, there is no difference in getting snow on your car lights or on your windscreen, so how come your windscreen is not blocked by snow? Of course burning it away with a heat source is one solution, so using an incandescent light is one of the possible solutions, not necessarily the best one.
Good solutions usually come about with either carefully considering all possible situations and rigid design, or they evolve from practical experience. It appears that the LED light mounting (a mechanical problem, not a LED problem) is of the latter type...

[Anthony Lang]

I've seen LED lights here in Florida (no snow problem here) that have gone out in groups of 4-6 LEDs leaving a gap in the light. A few days later, that same light is missing another couple of strings and the next week only about 2 or 3 strings of lights are lit.
Seems that this is a quality control issue as much as poor design.
LEDs have great potential. I have one here, an array, that puts out over 2000 lumens at about 21 Watts. Put 3 of these and their power supplies in each lamp and you're still energy efficient (one switches in when the other goes out) and very bright.

[Robert E. Yablonski]

Here in southern California a lot of the lights have multiple LED's out. This starts with a few and within a few days the segment (red or green or amber will be out). This is a very frequent occurrence.