I don’t think I’ve ever seen a stoplight bulb out of operation, even though most of them are active for a long period of the day. How often do stoplight bulbs need to be changed?
Life a traffic light? I think most of them are LED now.
The old incandescent bulbs lasted 2-3 years, give or take a bit - the green and red are on longer than amber. Overall, the bulbs are usually rated for 8,000 hours life.
Burned out traffic light bulbs used to be far from uncommon. Could cause big problems on intersections with only one traffic light fixture or if the burned out bulb was for a turn arrow. I actually saw one 3-4 years ago on a metered on-ramp. It took a few days until it was fixed.
Haven’t really seen one on a regular traffic light for quite a while - certainly due to the ubiquity of LEDs.
ETA: I can also hypothesize that when traffic light controls moved on from cam or relay based systems to electronic controls that the lifetime of incandescent bulbs may have improved due the limitation of inrush current to the bulb so less mechanical shock to the filament.
One unforeseen consequence of the shift to LEDs is that in northern climes you can get a build up of snow or freezing rain on the light. The less efficient incandescent bulbs would melt off the precipitation after a few cycles, whereas the LED would not. They had to go back and add a sensor and a heater to keep the lights clear.
I’ve heard that from various other outdoor lighting fixtures too and I’m wondering why did the politicians buy the waste heat argument agains incandescent bulbs. I live in Finland and here there is no waste heat as even during the summer most of time heating is required in apartments. Still EU banned incandecsent bulbs because of the waste heat “problem”. When one tried to argue that other types of bulbs are harder to manufacture, make more waste during manufacture and cost more to recycle, nobody cared.
And now we are installing heating elements because we don’t have the “waste heat” that was there to do the work.
We should start to lobby to get incandescent bulbs back. They are still manufactured, but in much lower quantaties, because there are uses where led based bulbs don’t work. So to just allow them to be used elsewhere would be the solution.
I suspect–but cannot prove, of course–that the lower replacement costs* make it worthwhile to use LEDs. Plus a wee bit of power savings (minimal, but still there). Even with the sensor/heater (which is also a sunk cost at this point).
Edit: *I mean that less frequent replacement saves money, not that LED bulbs are cheaper. I’m assuming they get decent LED bulbs, not the crap that dies after six months.
Many years ago, I recall reading an article by a color-blind person who mentioned that the “green” (incandescent bulb) traffic signal was “blue” enough to be readily distinguishable. Then I noticed that the new green LED’s were a more pure green. Now it appears that traffic lights are being adjusted:
LED Traffic Signals Get The Green Light Countrywide
In any event “waste heat to melt ice” would only be a concern when it is below freezing. Here is an analysis of LED savings when heating is not a concern:
https://www.yakimawa.gov/services/streets/led-traffic-signals/
I expect that the old ones were changed on a schedule, probably at night or otherwise during a low-traffic time, so burnouts would be much rarer than, say, burnt out lightbulbs at home are, where people basically just wait for them to burn out then change them.
If you replace on schedule, then the only burnouts you’ll notice are the bulbs that last less than their anticipated lifetime. Those bulbs probably aren’t cheap, but losing some unknown random length of lifetime is likely not worth screwing up traffic while people are trying to get somewhere.
Incandescent bulbs used in traffic signals will often last longer than 8,000 hours. That’s because the bulbs are rated for 8,000 when operated at 130 V, and thus will last considerably longer when operated at 120 V (which is what they’re operated at).
Here in the 'burbs, the traffic lights are all modern smart lights, probably the modern LEDs that were mentioned, and I never seem to see any burned out lights. In Chicago, however, the traffic lights are very, very old. i see dead lights quite often.
Smart lighting systems for street lights can run diagnostics on each lamp to get an indication of lamp ‘health’. IIRC, the electrical characteristics at start up such as current and voltage variations can be used to predict if a lamp is likely to fail, and be replaced before they actually fail. I imagine that some traffic light controllers can do the same.
BTW, smart streetlights can do interesting things such as dim when no traffic is detected and increase illumination as cars approach, or dim on a schedule when traffic is low like from 1 am to 5 am. Boring to everyone except facility and infrastructure managers.
A big factor in favour of LEDs for traffic signals, which would outweigh the issues of adding heating in some climates, is that their service life.
Every time a bulb blows the nearside traffic lane needs to be closed to do the replacement. Anyone who’s ever worked on a ladder in a closed lane near a busy live intersection knows how unsafe that is. Replacing incandescent globes with LEDS [with or without heaters] dramatically reduces the amount of unnecessary risk workers are being asked to take on.
How long have LEDs been a thing? I don’t recall seeing one burned out when I was a kid. And I’m 51.
I remember them as a kid, and I’m 36. It happened a handful of times. I remember even figuring out that this is why there were always at least two sets in any direction. One green light or red light would go out, but the other one was still there to tell you what was going on.
I am not entirely sure, but I seem to remember there being an issue where both greens went out, and they put the traffic light in stoplight mode, where it would either flash red lights in all directions (making it a four-way stop) or the more common way would get yellow flashing lights instead (making it a two way stop). However, that would also happen for other reasons I’m not aware of.
I also remember the first time we got a traffic light that could detect cars on it. It was the one by the gas station we preferred, which was not on the main roads. It was a situation where the most common traffic was a left turn one way and a right turn the other way, but there was occasionally some traffic from the other directions. By default, I believe it was green on the left turn direction and red on the right turn direction, but it would switch if when people came the other way.
I remember being fascinated by how it worked. Every other traffic light I knew ran on a timer. You could tell because they’d all change at nearly the same time.
LED traffic lights use arrays of small LEDs for each light. This means that if some fail, the light will still be understood by drivers, allowing a more convenient window for replacement.
A minor advantage of LEDs is that they illuminate faster than incandescent bulbs. This means a millisecond-scale improvement in apparent reaction times because an LED red light is perceived faster. Of course, it’s trivial with traffic lights to “lead” the drivers slightly for the same effect.
But there’s a real benefit for LED brake lights on vehicles—panic braking is inherently unpredictable, so LED brake lights reduce (slightly) the severity of accidents and prevent a few altogether by giving the driver behind more time to brake or swerve. Given the millions of cars on the road in the US, LED brake lights have a small but nontrivial effect.
“White” LEDs are different—they’re usually UV LEDs with a phosphorescent layer. The UV light makes that layer emit visible “white” light, and firing up the phosphors takes a perceptible amount of time. But those aren’t used for traffic or brake lights.