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Simple streetlight hack could protect astronomy from urban light pollution

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Re: Simple streetlight hack could protect astronomy from urban light pollution

#91

Post by bhickey »

kaybe wrote: post #73
uoaei wrote: post #63

Earlier quoted context omitted.

I often wonder how cutting and folding a bit of sheet metal and bolting it onto the streetlight as a shroud is overlooked whenever streetlights are built or repaired. There's one that shines directly into my bedroom but there's no good reason for it to illuminate any part of the building I live in.

Try contacting your city about it. Here they will come around within a few weeks and do as you suggested if you complain.

Yep. This is low hanging fruit for making constituents happy. I emailed my city councilor about this because I couldn't figure out who to ask at public works. The next morning a work truck rolled up and installed a shield on the light nearest to my house.

Re: Simple streetlight hack could protect astronomy from urban light pollution

#92

Post by tejtm »

nightowl_games wrote: post #8
bradley13 wrote: post #5

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…

> 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.

Even worse is Why pay to occasionally faintly illuminate the bottoms of airplains ever?

Re: Simple streetlight hack could protect astronomy from urban light pollution

#93

Post by sleepybrett »

cjensen wrote: post #86
amluto wrote: post #60

No. The article is light on details, but: > A simple device that makes LED lights flicker at a very high frequency that is imperceptible to the human eye > shutter, which needs to be lightweight and agile enough to blink about 150 times per second. Subjecting an entire city to 150 Hz flicker is not even remotely acceptable. IMO this needs to comply with IEEE 1789.

Why do you think 150Hz is unacceptable? People used to watch 50Hz TV, and weren't bothered too much. And San Jose used to use 60Hz flickering streetlights (sodium? not sure) to reduce light pollution for Lick Observatory.

because tvs used phosphors it isnt really on/off 50hz just a slight light dip.

Re: Simple streetlight hack could protect astronomy from urban light pollution

#94

Post by quickthrower2 »

p1mrx wrote: post #88
quickthrower2 wrote: post #84

Earlier quoted context omitted.

Plus you just add a position based delay. This is quite the bikeshed!

How does the LED know its own position? At that point you might as well abandon FM and use GPS.

Send a few bytes of data onto the SD card on lamp installation. If GPS can do it all in one then that is probably better given how cheap the units are these day.

Re: Simple streetlight hack could protect astronomy from urban light pollution

#95

Post by jcalvinowens »

namibj wrote: post #81
jcalvinowens wrote: post #35

Earlier quoted context omitted.

I feel the same way. If I'm sitting still I find I don't care much... but if I'm working with my hands and moving around it drives me crazy and gives me headaches, especially if I'm focusing on something spinning. Just for fun, I replaced the LED dimmer in my garage with a homemade board that has a frequency knob in addition to a duty cycle knob. I've found that the cutoff for bothering me is around 10KHz, which is f…

Could it be that you inadvertently smoothed the visual flicker on the electrical side? Consider fast brightness sensor with known (ideally approximately linear) sensitivity to the AC component of brightness, and check with an oscilloscope or so. A soundcard with 96 kHz sample rate should probably have a high-enough filter cutoff to be quite and easily useful there, though I'd see to check the frequency response with…

That's a great point: above some frequency, the inductance of the system starts to average the voltage like the output of a switching power supply.

I did think of that: I used a camera with a rolling shutter image sensor and manual exposure settings to prove to myself the LEDs were really still getting the full swing at higher frequencies. Also, to be clear, I'm talking about 12VDC COB LEDs with hard on/off PWM dimming, not A/C ripple.

I don't know, but I'd expect the cutoff frequency to be a lot higher. The self inductance of 30ft of 16awg wire is about 20uH. I should test it...

Re: Simple streetlight hack could protect astronomy from urban light pollution

#96

Post by anon_cow1111 »

calamari4065 wrote: post #87
galdosdi wrote: post #10

Earlier quoted context omitted.

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,…

Okay, let's do some math. Very rough napkin numbers, but it'll get us close. A 150Hz blink rate means a period of 1/150s, or ~6.7ms. The speed of radio signals through air near the surface is a bit lower than c, let's call it 299,250 km/s. [0] When you multiply those numbers you get ~1500km. That means each 'on' and 'off' signal is 1500km long, moving near c. More specifically, the signals are concentric rings around…

>Let's look at London. I picked it at random, but it just happens to have a land area around 1500km^2

Um am I really really tired and not reading correctly, or is this confusing linear area with square area? London doesn't stretch from New york to Florida.

186000 miles/second * pulse of .003 = 558 miles ~= 900 km

Re: Simple streetlight hack could protect astronomy from urban light pollution

#97

Post by jMyles »

I recently spent a week in Sisters, Oregon (where Thompson Guitars is making me a beautiful walnut guitar which I can't wait to play for y'all at future tech conferences).

I fell completely in love with the city on my first evening there. It took me a few hours to realize why: there are almost no streetlights. The main drag (Cascade Ave) has tasteful, downward-angled, orange lights. And the rest of the city has none at all. And. it's. awesome.

You can be standing in the middle of joyous nightlife, in earshot of two different live bands, and still see a stunning sky full of high desert stars. Each business lights their little strip of sidewalk as they see fit.

And it really hit home: It's 2023. The idea that light is an essential safety feature is one whose time has past. 90% of folks have a flashlight on their phone at the ready, and for anyone who doesn't have that privilege, or whose battery is dead, getting light shone in one's direction is as simple as shouting, "help me! I need light over here now!"

Being around the edges of the city at night is absolutely marvelous, especially on a bicycle.

Sisters has ignited in me a belief that streetlights are on their way out - coming to a city near you.

Re: Simple streetlight hack could protect astronomy from urban light pollution

#98

Post by rsaxvc »

globular-toast wrote: post #58
bradley13 wrote: post #5

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…

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.

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

Re: Simple streetlight hack could protect astronomy from urban light pollution

#99

Post by mortify »

op00to wrote: post #62
amluto wrote: post #60

No. The article is light on details, but: > A simple device that makes LED lights flicker at a very high frequency that is imperceptible to the human eye > shutter, which needs to be lightweight and agile enough to blink about 150 times per second. Subjecting an entire city to 150 Hz flicker is not even remotely acceptable. IMO this needs to comply with IEEE 1789.

Why not?

Flicker at certain frequencies isn't noticeable to humans in isolation. Add in other types of flicker (lights at other refresh rates, monitors, TV's, etc) and you can see the interference between them.

Re: Simple streetlight hack could protect astronomy from urban light pollution

#100

Post by rsaxvc »

bradley13 wrote: post #5

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…

> 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.

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