Simple streetlight hack could protect astronomy from urban light pollution
space.com
space.com
It causes light to flood into homes, and more than half isn't even illuminating the road. They also have no diffusion, so its harsh on the eyes. A bad design all around
A bit of background for those who may not be aware, white LEDs are UV LEDs with a white light emitting phosphor. I suspect 2800 K LEDs are a UV LED with a 2800 K light-emitting phosphor.
Edit: I wonder what gets used in "rich" places in contrast to "poor" places. I feel like rich people get the night sky and poor people get headaches and insomnia. So sick of this shit
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?
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.
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 the transmitter 1500km in width.
Let's look at London. I picked it at random, but it just happens to have a land area around 1500km^2. Assume the transmitter is in the center of the perfectly circular city, that means it takes 3.3ms for each 'on' and 'off' signal to cover the entire city. Each on and off pulse is just about exactly long enough to cover the entire city.
All that together means that at any given moment 50% of the lights in the city are on, and the other 50% are off. That's about as far from synchronized as you can get, really.
Also, light is slightly faster than radio in these conditions[1]. The light reaching the center of the city won't be pulsing in the same phase as the signal you're sending out. It will also be blurred and muddied due to the difference in signal speed. You probably wouldn't see much flicker in the light at all, as 50% of the lights are always on. On average, you receive 50% of the light you would otherwise, but that value will never reach 0. There won't be any periods of total darkness where you can make an observation, as the article suggests.
Moral of the story: light (and radio) is much, much slower than most people realize.
[0] https://ieeexplore.ieee.org/document/170108 [1] I couldn't find a confident number in my 16 seconds of searching. Seems like just a few percent faster, but the real number doesn't matter here.
Bonus: you can synchronize the streetlights exactly, but it's much more expensive and complex than a single radio transmitter. You need to have every single light contain a receiver with an accurate clock that synchronizes with a geosynchronous satellite with an atomic reference clock. Search for "GPS disciplined oscillator" if you're curious.
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
Either way, propagation delay is a huge problem with synchronizing systems. It's not something you usually think about
Better solution is less lights, or turn them off at night or any of the other solutions we've been talking about for 30 years. Remember when street lights were killing sea turtles?
The physics of radio wave propagation are surprisingly complex. Buildings and objects in the path between transmitter and receiver can cause various interference effects that basically slow down the signal. I'm glossing over a lot, but it would take significant effort to precisely measure the exact delay between any one receiver and the transmitter. It's much more complicated than just the distance, and each one has to be measured individually.
I'm not an expert in RF, but I think this concept of a single synchronizing transmitter just doesn't work in the real world. You'd probably build a cell network with many transmitters covering small areas. Each transmitter has the hardware to synchronize with thr others, and the lights just have a simple circuit slaved to the transmitter clock.
There's probably more clever ways to synchronize signals over long distances, but RF is black magic to me.
The wavelength of the control signal doesn't seem relevant.
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?
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.
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.
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 ...).
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.
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.
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]?
I believe relatively dim, warm coloured lights are a much better idea.
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.
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.
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.
I agree with you, though: lights blinking off and on all the time are not great. I drove somewhere in Europe where they did that with streetlights on major roads, and found it startling, long past the point at which I'd have assumed I'd become used to it. It wasn't the ones that were responding to me, it was the ones that responded to traffic on the opposite side of the road - they'd flash on in my peripheral vision and make me jump. Did not like.
That's only if they're moving within the sensors that switch on the light.
> The problem with warm lights is that they are much harder to see in the dark.
Not sure what "in the dark" means here. Light by definition is easier to see in the dark than it is in light as it has less light to compete with.
In any case, I find warm lights much easier. Cold lights are too much sensorial information for me. In any case, street light at night shouldn't be meant to allow you to see everything like it's a sunny day. It's supposed to give you enough light that you can see your surroundings and potential threats around you. For that, warm lights should be more than enough. If you need more light clarity, light your own phone torch or something.
Good point! In this case of nighttime lighting infrastructure it has become so vastly overbuilt as if to save people “the trouble” of these simple targeted solutions.
And that is the other reason. Those would still make nights look like nights, they should look sort of moonlight like with reasonable brightness.
Dim, but cool coloured lights? That's certainly better than bright cool ones but I still find them very annoying and overstimulating at night.
The only thing I can't do with dim, warm lighting is read small text from something other than a backlit screen. For everything else, it's perfectly fine. And if I do see myself having to do that, I'll just add a spot of light to what I'm trying to read, problem solved.
A few years ago I lived in a neighbourhood where all the street lights had a dark yellow tint, very warm coloured. They weren't all that bright either. I could see a person a block away with ease.
Again, that was far from ideal to read a book, but why would I do that out on the streets at night?
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.
Even if you somehow got it to work, one guy with a hacked flashlight could throw the whole thing into chaos.
This 150 Hz flicker may be above the flicker fusion threshold [0] for humans, but not for many animals. Excess lighting hours already massively screw up everything from sleep cycles, feeding patterns, growth patterns migration patterns, etc. in insects, birds, mammals, and plants, and contribute to the human caused mass extinction. Making it flicker would only exacerbate it. Perhaps if the flicker was at a rate in the kHz region, it wouldn't add to the interference.
But the best idea is to either ban lights altogether, or put them all on motion sensors, so both public and private lighting is turned-on only when needed.
Such a weird statement to make. LEDs are not somehow intrisically brighter than other light sources, it is simply a design parameter. If new LED lights are brighter than whatever they replaced, it is because someone purchased lamps with higher light output, not because they are LEDs. You can get plenty bright without LEDs too.
That said, do NOT shoot anything with a real firearm. Even small caliber bullets travel for miles. Walking out at 2am with a red ryder BB gun and plinking it would work just fine.
only if you miss
Or, depending how rural it is and how daring you are, you could put it on a timer yourself.
1.) the subservient: Get a good sleeping mask and blinds for your son 2.) the cooperative: work with the utility to put on a light shield 3.) the libertarian: shoot it
Human nature, encompassed in one thread. Beautiful, I love this site.
Cars have headlights. It could be that pedestrians can carry lights too. We could reduce infrastructure costs, electricity costs, allow pedestrians to be more conspicuous, and reduce the other negative impacts of constant lighting. You could even fund these personal lights for lower income people with the infrastructure savings.
Aye, on my midnight walks when I can't sleep (middle of nowhere - no streets, never mind street lights, it's all trails and fields. Amazing for stargazing!) I use my watch in flashlight mode to see where I'm going wherever it's particularly pitch black. I've also got a backup make-everything-daytime strength torch on me too if I need to properly see something or take out someone's night vision long enough to leg it
Never needed to use the latter so far. I don't imagine anyone trying to prey on me would even see me (or me them) until they're right up close if I turned the watch light off.
Fun tidbit for any new midnight walkers: Your night vision is separate in each eye. If you do need to use a light source in the dark, close an eye before you turn it on. That way when you turn it off you can open the eye and still mostly see where you're going while the other eye catches back up :)
I learned it doing backstage work at a theatre, I also heard it's the actual use case for pirate eye patches -- swap eye when going above and below deck. Good times.
As a kid, I also learned your eyes will individually adapt to not only brightness, but color.
The front door to the house was open and I put my face with my nose along the edge of it. One eye faced indoors, one eye faced outdoors. After a short amount of time I pulled my face away and it was quite clear that color in each eye had adapted to what it was seeing.
fun but weird.
Receiving bounced waves gives you information, while emitting it gives out information, and may make you a target. A streetlight is a neutral-emitter that doesn't usually need to worry about being attacked, unlike a bobbing flashlight held by someone walking in the dark woods.
A difference with car-headlights is that the car itself is a protective shell, and it's hard for other cars to hide in bushes.
So yeah, you can give out some information by holding a light, mostly about position. You give out much more information being in the light from street lights, such as sex, age, weakness/disability, etc that are more useful to criminals.
The are plenty of areas without street lights or with minimal street lights today. The primary issue as it pertains to crime is not a lack of street lights, but other factors such as socioeconomic factors and defensive knowledge.
We need to be reducing light pollution for the benefit of humans and other life forms, not just telescope machines.
The solution is less light, and more targeted, well thought out, aesthetically pleasing use of it. Warmer color temperature, shining it just where and when needed and reevaluating just how much illumination is wise and called for at night.
Are light bulbs actually being used in street lighting? I can't recall ever seeing that. Typically there's some gas-discharge lighting for that, and as far as I know, good old sodium-vapor lamps are pretty energy-efficient, on top of being not-terrible for astronomy.
This makes me wonder: what are LEDs replacing? And why are LEDs being installed rather than sodium-vapor lights? Is it because they are whiter? Cheaper to install? Just more hip?
I'd imagine some LED luminaries are consuming more energy than the sodium lamp they replaced, as they are usually brighter and some will have terribly inefficient power supplies.
I’ve seen in a number of places where the led lights have rapidly degraded, putting out really unpleasant bluish, purplish hues, as if the super bright daytime like sports field lighting everywhere wasn’t already bad enough. So this rapid degradation necessitating replacement no doubt eats into some of the cost savings.
Also, “cheaper to operate” mostly seems to have turned into “pump out more photons” instead banking the savings and maintaining nighttime lighting at non eyeball scorching levels.
https://fee.org/articles/why-are-some-us-street-lights-turni...
I’ve had issues with household LEDs that needed replacing well before expected lifespan.
I also saw this article some time back discussing issues with LEDs. https://nymag.com/strategist/article/led-light-bulbs-investi...
I’m not against LEDs, but the usage and implementation in a lot of cases to date could be better.
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 far higher than I'd have ever expected.
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...
If I'm just sitting typing on my laptop, even the 120hz ones don't bother me.
Well put. You can easily see flicker if you wave your hand in front of a flickering light source. The trail of your hand will look discrete, rather than continuous as it does with natural lighting.
Most light that flicker below 400hz really bother me, but I still perceive the surrounding as illuminated. While this particular torch light feels like "blinding darkness".
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.
Another possible concern may be that while the shutter is partially open, the resolving power of the telescope may be reduced, introducing diffraction artifacts into the image. A liquid crystal or Kerr cell shutter opens and closes everywhere across the full aperture at the same time, but they introduce polarizing elements into the light path.
The shutter in StealthTransit's current product is a leaf shutter, and for its original purpose of blocking satellite interference, the above concerns are probably not an issue, if the shutter is open almost all the time.
Around here, the LED lights do not seem brighter like the article claims.
Also, they are all full cutoff. In the past, almost all high pressure sodium streetlights meant to send light downwards had a glass globe below, which sent some light upwards. LED streetlights have flat panels instead, so none of the light fixture itself can directly send light into the sky. Only light reflected from illuminated objects and scattered by the air can light up the sky.
is there a reason to prefer these blue lights? (that are a bit uncomfortable for the pedestrian, so there must be a reason)
If monochromatic orange light is deemed undesirable it might be worth experimenting with mixing three monochromatic red, green and blue sources which also can be filtered out. The combination of the three produces something close to (but not identical to) white light which provides better colour rendition.
In fact, I think it's a bad thing. Night vision is better preserved with warmer colors. The bright blue daylight color kills our night vision which ultimately results in temporary blindness as we move away from the street light.
Maybe in the future when we all have smart glasses with night vision mode and self driving cars we’ll look back at citywide streetlights as a quaint and inefficient solution
A common mistake technologists make is to conflate the technologically illiterate with the entirety of the population. I can't overstate how technologically stratified we are and I believe his trend will only worsen. As technology advances, we will see the literate move forward and the majority stay relatively still. We will only see further stratification. We must assimilate this truth into our strategy.
I'm constantly distracted by light flickering in my peripheral vision. Computer monitors, traffic lights, car head and tail lights. Many modern LED lights are already flickering. It's often impercetible in my focused vision, but in peripheral vision is clearly visible.
I think it should be in the KHz at least...
My own solution is all area lights, streetlights, headlights, etc be a standard monochromatic red, low-energy and night-vision-sparing.
I doubt that’s invisible to humans, though, and am fairly sure it is visible to many animals species, including some pets. https://en.wikipedia.org/wiki/Flicker_fusion_threshold#Displ...:
“For the purposes of presenting moving images, the human flicker fusion threshold is usually taken between 60 and 90 Hz, though in certain cases it can be higher by an order of magnitude.”
That’s already awfully close to 150Hz, certainly if all lights you see do that, but let’s ignore that, and read on, where we find:
“In some cases, it is possible to see flicker at rates beyond 2000 Hz (2 kHz) in the case of high-speed eye movements (saccades) or object motion, via the "phantom array" effect. Fast-moving flickering objects zooming across view (either by object motion, or by eye motion such as rolling eyes), can cause a dotted or multicolored blur instead of a continuous blur, as if they were multiple objects”
and
“The flicker fusion threshold also varies between species. Pigeons have been shown to have higher threshold than humans (100 Hz vs. 75 Hz), and the same is probably true for all birds, particularly birds of prey. Many mammals have a higher proportion of rods in their retina than humans do, and it is likely that they would also have higher flicker fusion thresholds. This has been confirmed in dogs.
Research also shows that size and metabolic rate are two factors that come into play: small animals with high metabolic rate tend to have high flicker fusion thresholds.”
TLDR: I don’t think this is a good idea, especially not given that the actual problem (FTA: “But there is a downside to LEDs: They're much brighter than old-fashioned energy-guzzling light bulbs”) is easily avoided. It’s not like we couldn’t replace light bulbs with LED lighting of equal intensity (and directed in the same directions)
So only works for astrophotography, will increase exposure times, not likely to catch on since it only works for astrophotography. Unless entire cities, including parking lots, adopt them, it will only help with direct stray light, which isn't that much help.
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.
I don’t know why TVs weren’t headache-inducing. Certainly old CRT computer screens were extremely unpleasant to look at at lower refresh rates.
150Hz is well below the human perceptual threshold but still within the range that can cause problems.
Turn off the lights.