If you’ve ever set a telescope up in your backyard, you probably learned how quick any kind of lighting ruins your observation. In fact, a recent study found that every year, about 10% of the stars that were visible the previous year disappear in the mishmash of light scattering through the atmosphere. A company called StealthTransit has a solution: blink the lights in a controlled way. They have an animated video explaining the concept.
The technology, named DarkSkyProtector, assumes there is LED lighting and that the light’s owner (or manufacturer) will put a simple device in line that causes the LED to blink imperceptibly. As you might guess, the telescope — presumably some giant observatory uses a GPS receiver to synchronize and then images only when the LED lights all turn off. That presumes, of course, that you have a significant number of lights under control.
It is hard to imagine every city and home having astronomy-safe lighting. However, we can imagine a university installing a lighting system on its campus to protect night viewing. The system underwent a test in the Caucasus mountains using a 24-inch telescope and was apparently quite successful with a shutter rate of about 150 Hz. We weren’t clear if each LED control module has to have a GPS-disciplined time source, but it seems like you’d have to. However, the post talks about how the bulbs wouldn’t cost more to make than conventional ones, so maybe they don’t have anything fancy in them.
You can see satellites in the day with some tech tricks. Want to check out observatories? Hit the road. Or, get time on a telescope with Skynet University.
Doesn’t really matter whether it’s LEDs or any other form of lighting, it’s all a PITA for astronomy/astrophotography. LP filters are usually the first port of call depending on the type of light that is polluting your viewing.
For home use, I can see it not being that good, multiple light sources, firing at different frequencies depending on the drivers, feels like it would be impossible to sync the shutter. It also feels like these same issues could occur between cities and observatories. Not entirely sure how this would work with long exposure astrophotography too.
These are only personal feelings on first viewing, would love to hear from anyone that knows more about this…
That having been said, they do say that it’s for observatories and cities to co-exist but these days, afaik, scientific observatories are placed well above sources of light pollution, with all/most of the lighting turned off on location, maybe some low-level red lighting and decent lamp shades to stop the light leaking up.
As you say, this might be a partial solution in some situations, but the observations I’m involved in (asteroid occultations) require relatively long and continuous exposures (100-500ms) on very precise time frames, so this is unlikely to be of any assistance there.
Interestingly (to me at least); back when mercury vapor lights were popular for outdoor lighting, you could get notch filters for that frequency that resulted in surprisingly dark skies even in urban locations. Granted, mercury vapor light is pretty hideous for exactly the same reason.
I think you mixed it with sodium lights. Ugly yellow monochromatic lights are sodium vapor lights. Mercury vapor lights are outside of visible spectrum and need a flurescent coating to get acceptable white color.
According to Wikipedia (and other sources, but copy paste on phone is painful), Mercury vapour lamps have a few emission lines in the visible light range, and were often used without phosphors (phosphors might have also had specific lines anyway?)
So the claim of a useful filter, by the guy who says he works in astronomy, is completely plausible.
> Clear mercury lamps produce a greenish light due to mercury’s combination of spectral lines.
https://en.m.wikipedia.org/wiki/Mercury-vapor_lamp
Us astrophotographers don’t always image in the visible spectrum either.
I happen to know that the commonly available filters for the camera lenses of amateur landscape astrophotographers happen to be made for notching out sodium lights, not mercury.
Everyone correcting me is correct – I was referring to sodium lights and misspoke. Thanks for the sharp eyes!
I wonder if they tested these things around people with photosensitive epilepsy.
At the rate frequency these blink (I think the article says 150hz?), even if you have epilepsy, you couldn’t possibly be effected by this setup. You would need super human eyes to register that kind of refresh rate.
Lights already blink at 120Hz due to AC.
Well, I am not sure what the mains frequency is in the caucus mountains.
It’s Europe, so 50 Hz.
I mixed up Kaukasus with Carpathian mountains, but it’s still 50 Hz.
But at least Georgia is usually considered to be part of Europe.
Most don’t flash now, partly because that’s horrible – many people can see the flashing out of the corner of their eyes.
They’re filtered now so they don’t. It started with some flurecent lighting and now every single LED lightbulb feeds stable, completely-ripple-free DC to the LED chips.
“now every single LED lightbulb feeds stable, completely-ripple-free DC to the LED chips.”
Err, okay? I don’t know about the quality of industrial lights and street lights, but consumer LED bulbs can be very cheaply made.
The last one I’ve took apart (after it started to blink) did contain merely a single diode. No capacitors, no filtering.
Not sure how this compares to the goold old days of incandescent lamps (they could be used for light phones), but the latter had a latency due to the afterglow of the filament/wire inside.
So I suppose incandescent lamps were rather getting brighter and dimmer in a smooth way.
Not hard on/off like the other types.
PS: Sorry for my poor English.
Nothing wrong with your English Joshua, it’s better than some native speakers that I know!
The incandescent bulb filament did not cool fast enough to detect easily, and as a pure resistance it was heating at any voltage and the AC gave peaks of the power at 120Hz.
Rectified AC to 100Hz or 120Hz. I think LED low voltage systems use a switching supply for DC. The lamps with a bunch of LED in series? I don’t know. I have replacement LEDs for fluorescent tubes and detect no flickering visually or on video or digital photos.
I wonder how this would affect wildlife. Birds, for example, have a much higher image fusion rate than humans.
It’s the light spectrum, I suppose.
Blue light attracts insects, if they see blue they think it’s their “red light” district. ;)
Jokes aside, energy saving bulbs and “white” LED bulbs are the worst here.
Manufacturers try to filter blue out by using frosted glass and other tricks.
In my street, last year, they had mounted insect traps under those blu-ish street lights. These were big bags made of fabrics, essentially,
After the test was finished, we got yellow/orange street lights.
As a side effect, these lights are much less eye straining to human eyes, too.
So it can be done. 🙂
Surely the easiest solution is simply to mandate some deliberate and narrow slightly yellow part of the spectrum (or even something that approximates white very well to our eyes, but made up of only a few very distinct wavelengths) for vehicle headlight and outdoor lighting, maybe put a little bias towards it for general lighting too. Then you can filter out most of the light pollution very easily, and it will have virtually no impact on everybody else – might even be beneficial as I know the full spectrum street lights really drive me mad at bedtime…
Also seems crazy to make lighting more complex – surely the mains electric’s periodicity and transition to LED has created something rather close to this idea naturally?
What if your scientific observation requires the yellow light?
Then you can at least be happy that a hypothetical science first system replaced the current mess.
I thought it was red. I do remember that SkyMap on Windows 3.1x had a “night vision” mode that gave everything a red tint. ;)
Except we put a lot of smooth out any ripple in lights as human eye can still see 100/120hz ripple and we also put a lot of effort into making their spectrum as continuous as possible as while your eye may not distinguish 633nm red from 680nm red the apple skin reflects only one time of red and if you illuminate it with not spectrum continuous light you may get black apples.
Yeah the flicker is smoothed as if you don’t its murder on the eyes, but it is still there and related to the grid so it can be filtered out over a bit of capture time.
And from the POV of useful outdoor lighting or vehicle lights you don’t need high quality CRI lighting, you just need to be able to see well enough. People got by just fine with with the old yellow hue streelights and headlights for decades and those were pretty easy to filter out to a useful level. Largely because nothing is that perfect your light is going to have some spread, and objects are pretty much never that uniform in colour – that apple isn’t only 680nm its a whole range of reds, probably more than a bit of yellow etc – you won’t get it looking as it should in daylight, but it will still look like an apple, and probably still be clearly a red apple.
Driving at night used to involve very minimal glare – partly because lights were dimmer and the light was spread out more across their surface area and across a beam with a softer cutoff, but partly because they didn’t have much if any blue in them.
I sometimes wear glasses which filter out the light destined for my blue cone cells. While they don’t dim other people’s headlights as much as I’d like, they do improve contrast since the bluer light gets scattered and diffused so much not only in the world but in a human eye. That’s why “blue” (violet 405nm) laser pointers at a distance look like they’re out of focus, but when you walk closer you see they aren’t – your eyes don’t do a great job at those wavelengths, and even at the wavelengths of the blue that LEDs use to power their phosphors (440-450nm) glare is worse than ideal.
I guess it cuts also sensors exposure time, dimming the stars as well in the resulting image.
In the photos at the top of the article, I can see more stars in the “polluted” one.
I tried setting my display gamma to 3. Several hundred stars are visible in the dark image.
At 150 Hz you don’t need GPS dicipline. NTP over wifi is good enough for that.
Recovering a clock signal from the mains is how we used to do it back in my day…
Use a PLL to generate a high frequency flicker, phase locked to the mains supply, I imagine 150hz or 300hz would be easy to achieve and won’t be noticeable by humans.
Very cheap and will allow synchronizing all lights in the area without any “smart” components.
Then use the same idea to synchronize the telescope.
A light sensor may be enough to sync with the ambient light flickering.
Maybe my attention drifted while reading, but doesn’t this require a mechanical shutter for the camera? Like the spinning disk with a slot in a movie camera? The CCD sensors I know of can not be read fast enough for this scheme to be done without a shutter. Honestly, it sounds ridiculous. Start a gofundme to put a nice shared telescope at a Lagrange point. Or in LEO. SpaceX has very affordable rates, even for geosync.
It was a thing in Europe for a while to do a concerted effort to reduce light pollution, with all cities/towns doing an effort. (in practise it meant lights that are aimed down, and less unnecessary ones.)
I think it started to be forgotten that that was the plan in a few months with the amnesia spreading steadfastly, and now I bet if you mention it they will say you imagined it and it never happened, and you’d probably start to doubt yourself…
I think there are still some light being installed that take it into account, but I bet even the people managing the installing of lights would not know why they are doing it, it’s just a vestige with a forgotten purpose.