6 ms·

Right. They're going to get all the streetlights in an entire city to blink in unison. Sure they are. Anyway, in most cases the LEDs don't run at 100%. In our

Right. They're going to get all the streetlights in an entire city to blink in unison. Sure they are. Anyway, in most cases the LEDs don't run at 100%. In our area a, I happen to know that they are between 29% and 40%. That dimming is accomplished by blinking. Which would conflict with the idea of having them blink synchronously. Much simpler solution: ensure the LEDs ghts are directed exclusively downward, and have only as much illumination as needed. Even better: turn the darned things off when they are not needed - why illuminate empty streets?

nightowl_games 3y ago
> Even better: turn the darned things off when they are not needed - why illuminate empty streets? That is a way better idea than the one in the article, for sure. So many benefits. Would need the motion sensing technology to be top notch tho. Need to illuminate for pedestrians as well. Or perhaps illuminated sidewalks, or smaller lights for pedestrians.
- Marsymars 3y ago
  Some of the newer street lamps in my area have smaller light for pedestrians! They're mounted at human height and shine down on the sidewalk. Motion sensing, I find, similar to LED technology, is often used more for increasing lighting levels rather than decreasing. My pet peeve are people who have motion sensors that activate their 20k lumen floodlights based on motion on the public sidewalk. Cities should not allow those.
  - sokoloff 3y ago
    > Motion sensing is often used more for increasing lighting levels rather than decreasing Isn't that just a matter of perspective [whether the presence of motion is used to increase lighting or the absence of it is used to decrease]?
- ikekkdcjkfke 3y ago
  I it find harder to see objects under street lights than a person with a head lamp or a car, everything just blends into one color
- Anotheroneagain 3y ago
  No it's a horrible idea, imagine the lights turning on and off as people pass. No!
  - cassianoleal 3y ago
    Indeed that would be terrible, especially in dodgier areas. Not only you're advertising your position to potential attackers, but you're also less likely to see them until they're very close. I believe relatively dim, warm coloured lights are a much better idea.
    - canoebuilder 3y ago
      Last sentence is a fine idea, it is also possible to move toward developing a society where “potential attackers” is a thought much more distant in people’s minds.
      - cassianoleal 3y ago
        > it is also possible to move toward developing a society where “potential attackers” is a thought much more distant in people’s minds Amen, but alas we're not there. In any case, threats don't always come from purposeful attackers. It's useful to see animals, vehicles and bikes with no light, etc.
        canoebuilder 3y ago
        >Amen, but alas we’re not there What is troublesome is that many places, that many of us probably hail from, “were there” not so long ago, and it was destroyed by duplicitous, malicious political and cultural actors. Having “safe streets” is not a pipe dream. Indeed not having them is a symptom of people trying to destroy our societies.
    - Anotheroneagain 3y ago
      You could see the attackers just as well as they see you. I meant because of the annoyance that it would create. The problem with warm lights is that they are much harder to see in the dark. Maybe dim lights around 505nm would be a better idea.
- tejtm 3y ago
  Even worse is Why pay to occasionally faintly illuminate the bottoms of airplains ever?
galdosdi 3y ago
I'm not sure I'd be so quick to dismiss the feasability, at least not based on your reasoning so far. FM Radio stations have managed to accomplish getting the speaker in your car radio to "blink synchronously" according to a complex signal pattern in the exact same way as millions of other radios simultaneously.... for about a century now. As long as all streetlights are in locations with good radio reception (which, since they're all on streets and are tall, is likely), it would not be that hard to implement in principle a central FM or other radio signal that oscillates according to the expected blinking. Lights that are engaging in dimming could multiply another signal by the central signal to diminish it even more.
- coryrc 3y ago
  You must not be familiar with multipath interference. Radio isn't quite as synchronous as you believe it to be.
  - saltcured 3y ago
    And of course the light itself is also undergoing multipath distortions like the radio signal. And for astronomy, the changing atmosphere might be the most important secondary reflection. And the multipath arrangement between emitter and observer is different for each pair. Could you make a dark period long enough to mask the multipath variance among emitters and observers? Or would this dark period be so long as to cause annoying flicker?
- Evidlo 3y ago
  Wavelength of FM radio is about 3m, so you only have to be a few centimeters shifted to be seeing an entirely different phase and be out of sync.
  - p1mrx 3y ago
    If the LEDs blink at 150 Hz, then a single on-off cycle has a "wavelength" of 2000 km. The wavelength of the control signal doesn't seem relevant.
da768 3y ago
Why not, just sync them to the AC power grid they're all powered from.
- jcalvinowens 3y ago
  Different types of transformers introduce different phase shifts.
  - da768 3y ago
    Couldn't you still account for offset?
    - jcalvinowens 3y ago
      Maybe? I guess you could "calibrate" it with GPS. I don't know how consistent the phase at a specific location really is in practice on long timescales.
dahart 3y ago
Yes exactly, aim them downward and turn the unused ones off, which is most of them most of the time, and the problem will be solved for everyone. The reason we should do it is that it will save money and power for everyone, the night sky is just icing on the cake. Getting lights to blink in unison is a neat idea, and technically not hard nor too expensive for new lighting. Personally I think the biggest problem with it is that cities aren’t going to agree to overhaul all existing outdoor lighting only for the sake of people using telescopes. Even if there was widespread buy-in this is a project that could easy take 50 years or more, and cities might be reluctant to commit to this idea right when technology is rapidly changing.
- drpixie 3y ago
  Precisely. Why go for the complex, expensive, and fragile solution when better shades (and maybe proximity/motion sensors) would do the job?
klyrs 3y ago
> They're going to get all the streetlights in an entire city to blink in unison. Sure they are. Thre are a super simple and effective distributed algorithms for this, if each lamp can see another few lamps. They don't even need a good clock, just a relatively stable oscillator within a few percent of a standard frequency, a light sensor and an integrator. I agree that it's better to just put hoods on the lamps to direct the light to only where it's needed, but distributed synchronization is a solved problem.
- p1mrx 3y ago
  I find it difficult to believe that a city-wide distributed synchronization algorithm could actually work. How do you deal with the photo-electronic-photo propagation delay, and ensure that each sensor is paying attention to the correct emitters, possibly including itself? Even if you somehow got it to work, one guy with a hacked flashlight could throw the whole thing into chaos.
quietpain 3y ago
In Europe the entire mains grid is synchronised - the smallest deviation in fase & frequency is the same. It’s fairly straightforward to sync them with this distributed reference clock. Edit: https://www.mainsfrequency.com/ https://www.mainsfrequency.com/
- jcalvinowens 3y ago
  The frequency observed across all loads in the system might be very consistent, but the phase is absolutely not. Different types of transformers introduce different phase shifts, so this can't work.
globular-toast 3y ago
Dimming is usually done by pulse width modulation. So you can definitely get them to blink at the same frequency, you just change the pulse width.
- rsaxvc 3y ago
  They need phase locked too. Edit: article says they're using GPS, probably using PWM-aligned-to-PPS.
rsaxvc 3y ago
> Right. They're going to get all the streetlights in an entire city to blink in unison. Sure they are. The article states they use GPS for synchronization. I wish they went into it further, but a number of affordable chipset can do emit PWM at the proposed frequencies, globally aligned in time to PPS(every receiver computes the same top of second), then the telescope exposes during the blanking time. On a related note I have a 1MHz GPS time source in my office that is synced to a 10MHz OCXO(more common for test gear) so my equipment is phase synchronized to GPS. It's really spooky to sync the oscilloscope to one time source and probe another time source with the scope and watch how their phases don't perceptibly drift from each other.
ygra 3y ago
Where I live they installed street lights that are a lot dimmer by default, but they are connected and have motion detectors. Whenever someone comes near, the light gets brighter and so do the others in direction of travel. You kind of get a light wave traveling with you and afterwards they dim again. The mayor then got complaints that the street lights are not as bright as mandated by some regulation (when measured with an empty road in their dimmed state ...).

nightowl_games 3y ago

> Even better: turn the darned things off when they are not needed - why illuminate empty streets? That is a way better idea than the one in the article, for sure. So many benefits. Would need the motion sensing technology to be top notch tho. Need to illuminate for pedestrians as well. Or perhaps illuminated sidewalks, or smaller lights for pedestrians.

Marsymars 3y ago
Some of the newer street lamps in my area have smaller light for pedestrians! They're mounted at human height and shine down on the sidewalk. Motion sensing, I find, similar to LED technology, is often used more for increasing lighting levels rather than decreasing. My pet peeve are people who have motion sensors that activate their 20k lumen floodlights based on motion on the public sidewalk. Cities should not allow those.
- sokoloff 3y ago
  > Motion sensing is often used more for increasing lighting levels rather than decreasing Isn't that just a matter of perspective [whether the presence of motion is used to increase lighting or the absence of it is used to decrease]?
ikekkdcjkfke 3y ago
I it find harder to see objects under street lights than a person with a head lamp or a car, everything just blends into one color
Anotheroneagain 3y ago
No it's a horrible idea, imagine the lights turning on and off as people pass. No!
- cassianoleal 3y ago
  Indeed that would be terrible, especially in dodgier areas. Not only you're advertising your position to potential attackers, but you're also less likely to see them until they're very close. I believe relatively dim, warm coloured lights are a much better idea.
  - canoebuilder 3y ago
    Last sentence is a fine idea, it is also possible to move toward developing a society where “potential attackers” is a thought much more distant in people’s minds.
    - cassianoleal 3y ago
      > it is also possible to move toward developing a society where “potential attackers” is a thought much more distant in people’s minds Amen, but alas we're not there. In any case, threats don't always come from purposeful attackers. It's useful to see animals, vehicles and bikes with no light, etc.
      - canoebuilder 3y ago
        >Amen, but alas we’re not there What is troublesome is that many places, that many of us probably hail from, “were there” not so long ago, and it was destroyed by duplicitous, malicious political and cultural actors. Having “safe streets” is not a pipe dream. Indeed not having them is a symptom of people trying to destroy our societies.
  - Anotheroneagain 3y ago
    You could see the attackers just as well as they see you. I meant because of the annoyance that it would create. The problem with warm lights is that they are much harder to see in the dark. Maybe dim lights around 505nm would be a better idea.
tejtm 3y ago
Even worse is Why pay to occasionally faintly illuminate the bottoms of airplains ever?

galdosdi 3y ago

I'm not sure I'd be so quick to dismiss the feasability, at least not based on your reasoning so far. FM Radio stations have managed to accomplish getting the speaker in your car radio to "blink synchronously" according to a complex signal pattern in the exact same way as millions of other radios simultaneously.... for about a century now. As long as all streetlights are in locations with good radio reception (which, since they're all on streets and are tall, is likely), it would not be that hard to implement in principle a central FM or other radio signal that oscillates according to the expected blinking. Lights that are engaging in dimming could multiply another signal by the central signal to diminish it even more.

coryrc 3y ago
You must not be familiar with multipath interference. Radio isn't quite as synchronous as you believe it to be.
- saltcured 3y ago
  And of course the light itself is also undergoing multipath distortions like the radio signal. And for astronomy, the changing atmosphere might be the most important secondary reflection. And the multipath arrangement between emitter and observer is different for each pair. Could you make a dark period long enough to mask the multipath variance among emitters and observers? Or would this dark period be so long as to cause annoying flicker?
Evidlo 3y ago
Wavelength of FM radio is about 3m, so you only have to be a few centimeters shifted to be seeing an entirely different phase and be out of sync.
- p1mrx 3y ago
  If the LEDs blink at 150 Hz, then a single on-off cycle has a "wavelength" of 2000 km. The wavelength of the control signal doesn't seem relevant.

da768 3y ago

Why not, just sync them to the AC power grid they're all powered from.

jcalvinowens 3y ago
Different types of transformers introduce different phase shifts.
- da768 3y ago
  Couldn't you still account for offset?
  - jcalvinowens 3y ago
    Maybe? I guess you could "calibrate" it with GPS. I don't know how consistent the phase at a specific location really is in practice on long timescales.

dahart 3y ago

Yes exactly, aim them downward and turn the unused ones off, which is most of them most of the time, and the problem will be solved for everyone. The reason we should do it is that it will save money and power for everyone, the night sky is just icing on the cake. Getting lights to blink in unison is a neat idea, and technically not hard nor too expensive for new lighting. Personally I think the biggest problem with it is that cities aren’t going to agree to overhaul all existing outdoor lighting only for the sake of people using telescopes. Even if there was widespread buy-in this is a project that could easy take 50 years or more, and cities might be reluctant to commit to this idea right when technology is rapidly changing.

drpixie 3y ago
Precisely. Why go for the complex, expensive, and fragile solution when better shades (and maybe proximity/motion sensors) would do the job?

klyrs 3y ago

> They're going to get all the streetlights in an entire city to blink in unison. Sure they are. Thre are a super simple and effective distributed algorithms for this, if each lamp can see another few lamps. They don't even need a good clock, just a relatively stable oscillator within a few percent of a standard frequency, a light sensor and an integrator. I agree that it's better to just put hoods on the lamps to direct the light to only where it's needed, but distributed synchronization is a solved problem.

p1mrx 3y ago
I find it difficult to believe that a city-wide distributed synchronization algorithm could actually work. How do you deal with the photo-electronic-photo propagation delay, and ensure that each sensor is paying attention to the correct emitters, possibly including itself? Even if you somehow got it to work, one guy with a hacked flashlight could throw the whole thing into chaos.

quietpain 3y ago

In Europe the entire mains grid is synchronised - the smallest deviation in fase & frequency is the same. It’s fairly straightforward to sync them with this distributed reference clock. Edit: https://www.mainsfrequency.com/ https://www.mainsfrequency.com/

jcalvinowens 3y ago
The frequency observed across all loads in the system might be very consistent, but the phase is absolutely not. Different types of transformers introduce different phase shifts, so this can't work.

globular-toast 3y ago

Dimming is usually done by pulse width modulation. So you can definitely get them to blink at the same frequency, you just change the pulse width.

rsaxvc 3y ago
They need phase locked too. Edit: article says they're using GPS, probably using PWM-aligned-to-PPS.

rsaxvc 3y ago

> Right. They're going to get all the streetlights in an entire city to blink in unison. Sure they are. The article states they use GPS for synchronization. I wish they went into it further, but a number of affordable chipset can do emit PWM at the proposed frequencies, globally aligned in time to PPS(every receiver computes the same top of second), then the telescope exposes during the blanking time. On a related note I have a 1MHz GPS time source in my office that is synced to a 10MHz OCXO(more common for test gear) so my equipment is phase synchronized to GPS. It's really spooky to sync the oscilloscope to one time source and probe another time source with the scope and watch how their phases don't perceptibly drift from each other.

ygra 3y ago

Where I live they installed street lights that are a lot dimmer by default, but they are connected and have motion detectors. Whenever someone comes near, the light gets brighter and so do the others in direction of travel. You kind of get a light wave traveling with you and afterwards they dim again. The mayor then got complaints that the street lights are not as bright as mandated by some regulation (when measured with an empty road in their dimmed state ...).