A friend of mine recently brought this question to my attention. I had no idea of the answer, but I figured that if anyone would be able to provide an answer, you guys would…
On the tops of many street lights in New York City, there are these little orange thingies. They sort of resemble little orange lights. What the heck are they?
Zev Steinhardt
They’re photoelectric sensors. When it gets dark, they turn the lights on automatically, and turn them off when it gets bright enough. Usually not every lamp has one, and the sensor on one lamp can be used to control a bank of streetlights.
Thanks, Q.E.D., I knew someone would know.
This, however, adds a follow up question:
For many years (before those orange photoelectirc sensors) were installed, the lights would often go on and off at the appropriate times (including going on whenever it got extra dark on a cloudy afternoon). So, how did the lights go on/off by themselves before the sensors were installed?
Zev Steinhardt
Photosensors have been around a long time. They haven’t always been orange.
Right, and they haven’t always been on top of the lamps, either. Some were mounted as separate devices on top of a pole, for instance. Again, these would normally control a bank of lamps. I don’t know specifically what benefit the newer sensor types offer, but my guess is that they are less prone to false “off” triggering by car headlights and other artificial light sources.
Thanks a lot everyone. I appreciate the help and the quick answers.
Zev Steinhardt
I remember seeing street lamps here where perhaps one in ten lamps had a bump on top - a single photosensor controlled a whole row of lights (although sometimes, judging by the way they used to switch on, it seemed like it wasn’t a contiguous block of ten, but more like every third lamp in a row of thirty switching on at the same time.
I wonder what the economies were that drove such a system, maybe the sensors weren’t very reliable/durable, so the extra cabling involved in patching them together would be cheaper than the cost of continually replacing ten times as many sensors…?
Anyway, nowadays, street lamps seem to be equipped with their own sensors each and the technology has improved so that things like dark clouds won’t usually set them off; they have hysteresis to make them less sensitive to sudden brief changes (like a bird alighting on the sensor foir a minute) and they probably have some kind of circadian rythm thing; not so much a strict timer as a sense of whether it has been long enough since the last measured ‘night’.
Wrong. Wrong. Wrong.
The glowing LED-filled orange thingees, roughly shaped like tennis ball cans, on top of steet corner light ploes indicate that a fire alarm box is located on the corner. I know this because I asked the same question of the NY Times “FYI” column, and that’s what they told me.
It’s sort of the modern day version of a similar system that has existed for decades but is being fast faded out. If you look closely you can still find some orange bullet-shaped incandecent lamps poking out of street light and telephone poles. They too indicate a fire alarm box on the corner.
Maybe4, but that doesn’t seem to match the description in the OP. He said on top of the lights, which I took to mean on the topside of the lamp assembly, rather than the top of the pole. And he said they look like lights, but didn’t say they were actually lit. I can’t speak to the color of the fire alarm box indicator lamps in NYC, but in all the places I can recall seeing them they have been blue, not orange.
Perhaps some clarification on the details from the OP would help clear this up.
Look, I know exactly what the OP is talking about.
Sometimes the orange thingees are mounted on top of the poles; sometimes they are mounted on top of the streetlight “heads.” It varies, but they are all the same. And they are the only orange thing out there.
If the OP is talking about something like these, then they are not fire alarm box lamps, they are light sensors. This particular one is orange. As I said, some clarification from the OP is needed here.
Here is a better view of one. Is this what you mean, zev?
I know that if you fire a roman candle in an arc over a street light at night, you can turn off the entire string of lights connected to that sensor 
Showing my age here:
Back in the early 70’s (73 I think) we in the UK had a period of industrial strife + oil crisis which lead to power shortages and planned power outages. In those days the street lights contained a timer mechanism to turn on and off. Trouble was the timer was electric so it got all screwed up during a power cut. I remember adults complaining that we were all being asked to use less electricity, yet the street lights were burning at lunch time.
Yes, Q.E.D., that’s exactly what I was talking about!
Zev Steinhardt
And a carefully aimed laser-pointer can do the same thing…I’m told.
Is there a picture anywhere of stuyguy’s tennis-ball-can fire thingy for comparisson? Now, I’m curious.
Those things generally got their own branch off of a pole, like so (about halfway down the page).
Ok, so I stand corrected. A million pardons for my smart-aleciness, especially to Q.E.D. whose request for clarification saved the day.
Manhattan’s link shows the old-style, bullet-shaped fire signal lights that are currently being replaced by the longer, cylindrical (“tennis ball can”) style I mentioned earlier. The new style does not appear on that page.
S’alright, stuyguy. Coulda gone either way.
