One interesting property of LEDs compared to many other lighting technologies is that they can be turned on and off very quickly.

Suppose you made all your LED lights so that they alternated 2.08333 ms on, 2.08333 ms off. That's a 240 Hz flicker rate, which should be high enough that it won't bother people.

Further, suppose you synchronized the flicker of all the lights in a city so that they were all on at the same time, and all off at the same time.

Finally, suppose you made some goggles that had a shutter system opened for 1.5625 ms out of every 4.16667 ms, and synchronized it with the LED flickering so that the shutter opens 0.520833 ms after the LEDs start their off phase. The shutter will then be closing just as the LEDs turn on.

By the time the shutter opens, the LEDs will have been off for 0.520833 ms. Light travels 156 km in that time, so the last light from the on phase of all LEDs within 156 km of the goggles will have already reached the goggles by the time the shutter opens.

Question: would this effectively make the LEDs invisible to you through the goggles, while letting you see non-LED sources such as stars with no interference other than the 62.5% of their light you are losing during the times when the shutter is closed?

One problem I can see (no pun intended) is that many LED lights actually use a bulb coated with phosphors, and the LED in the bulb is used to excite the phosphors which then glow giving off the light that we see. I'm not sure how quickly the phosphor stops glowing when the driving LED turns off.

That’s a nice thought experiment but I believe reflection and scattering would still provide some sort of “after glow”

Even if a material reflects 100% of the incoming light, the light has to bounce around quite often in order to stick around for the time where the LEDs are off. In fact it has to travel 156 km somehow. Suppose a ray hits an object and doesn't get reflected. Then it has to be reflected at the right angle to hit another object, and another one and another one, until it has traveled the 156 km. Each time, it can also be reflected into the sky or be absorbed. I'd argue that within the time, most of the light will have escaped or been absorbed. Unless there are materials that have an after glow like you describe.

> One problem I can see (no pun intended) is that many LED lights actually use a bulb coated with phosphors, and the LED in the bulb is used to excite the phosphors which then glow giving off the light that we see. I'm not sure how quickly the phosphor stops glowing when the driving LED turns off.

Unfortunately this is how all white LEDs work, and the retention time is tens of miliseconds. It's an interesting idea though, based on the old shutter 3D goggles. Since it would rely on the eye adapting to the flickering darkness, it would be very dependent on how good the light seal round the edges of the goggles is.

Having everyone wear some high tech impressively synchronized googles would be cool and all, but why not just use an opaque or reflective cover?

What if "someone" is an astronomical observatory?

At least for greenhouses it might be simpler to require narrow-band LEDs and matching narrow-band filter glasses.

Isn't sunlight much more powerful in terms of energy than these lights? Couldn't we use a "one-way" mirror to reflect the led/lights inside, and still allow sunlight in during the day? The additional reflections inside the greenhouse might more than make up for the "shade" provided by the "one-way" mirror?

(now, AFAIK there are no actual one-way mirrors, simply semi transparent (both directions) - question is if we cut 70-80% of the leds escaping, would 20-30% sunlight entering be enough?)

LEDs are supplemental. Sunlight gives you about 1kW/m² for free, it's hard to beat that. So anything that sacrifices a large fraction of sunlight is probably a non-starter, especially during the colder seasons where you also need it to keep the glasshouse warm.

I suppose you could always go for semi-transparent - so not reflect but absorb a fraction of the light?

The problem would be that those narrow band glass filters would also block those narrow bands in daylight needed by the plants. They would have to have those LEDs on 24/7 which means a greenhouse is no better than a basement with no daylight.

I think they should simply use curtains or shutters that close at night. I'm surprised a modern country like Netherlands has no laws regarding light pollution.

I was actually talking about glasses for humans, but I will roll with your argument anyway:

Plants are not narrow-band absorbers. They can utilize rather wide ranges of red and blue light. So if you blocked out a very narrow band there they would still get most of the sunlight. During the night they would simply harvest photons from those narrow bands, they don't care. But the photons wouldn't escape the glasshouse.

But yes, shutters are probably much cheaper than narrowband light sources and matching filters.

Or just curtains?

I have a friend with a condition a bit like epilepsy and LEDs set him off all the time.

Attacks have even been brought on by passing cyclists with red LED lights.

Weirdly my older Phillips hue does not, so either that is not flickering or it is doing it much faster.

LED lightbulbs are different from the bare LED's on a bike light, they use blue LED's under a layer of phosphor that absorbs it and re-emits a variety of shorter wavelengths simulating white light and different colour temperatures.

Most cheap light fixture LEDs flicker. You can test easily using your mobile phone camera if it has a 120-240hz mode.

It would not work to fix the light pollution problem.

* Wild animals, don't have these glasses, so they will keep being strongly affected.

* The light get scattered on the atmosphere, buildings, clouds, etc, so a weird range of time shifts would occur.

* This wouldn't work if you are trying to do photos !

When landing at an airport at night in Vietnam, you can see this all over the landscape. Much of it is for dragon fruit in off season...

https://www.growables.org/information/TropicalFruit/DragonFr...

https://english.vietnamnet.vn/fms/science-it/187197/vietname...

Interesting links, thanks!

Here's an excerpt which I found particularly interesting:

"According to Nguyen Doan Thang from Rang Dong, the research team created more than 20 types of fluorescent powder to produce specialized lamps for chrysanthemum and dragon fruit tissue culture. The manufacturing processes are highly reliable, meeting the requirements for industrial production."

That is a pretty offensive amount of light pollution going on the glimpses of street lights and car headlights in the pictures.

We need a law where if they want to use those at night, they need to cover them up somehow (has to be retractable, because they'll still want free natural sunlight in the daytime).

That'll never happen though. "It costs too much".

So, they'll steal the night sky from us and give us nothing in return.

If public art is worth investing millions in per city, then what is the value of preserving the view of the night sky?

Why don't we just paint everything grey and all wear grey clothes and eat soylent every meal and have nothing left that's beautiful. We can work in windowless offices to save money on windows. Maybe we can cover up the sunset next.

Bah.

If you think the night sky hasn't been stolen already, then chances are you've just never been to someplace where it hasn't been. After that, it's all a matter of degree.

It would be fairly straight forward to have ordinances that limit light pollution--- do a night time flyover (perhaps via drone), issue citations to any property with more than Y illumination facing up after hour X on more than N days out of M.

But people don't care, perhaps because so many people have never actually seen a dark sky.

As an aside-- My own opinions on this subject changed after experiencing a really dark sky myself. I though I had before, e.g. being on a boat a few miles off Florida at night, but I hadn't-- not only is it not that dark at that distance but the humid air on the ocean reduces visibility.

For the 2017 solar eclipse I drove out to Hereford, Oregon for the best chance of being in the middle of the path with zero cloud cover-- which was a total success. My drive had me going up 395 towards wagontire at something like 3am and I took a break with the lights of the car off long enough to dark-adapt my eyes and see the night sky in some of the darkest skies in the continental US.

I do not exaggerate to say that although the eclipse was really neat, I found the moonless clear night sky considerably more impressive than the eclipse and considerably less well captured by pictures.

In talking about it to others I found that many people didn't know that the milkyway is perfectly visible to the eye, and not in some squinting barely visible sense, but in an awe inspiring "holy crap what is that?" sense... Many seemed to think that it was just some long exposure / multi-spectral trick like you often see in astronomy photos.

I grew up in South Florida where the gulf stream isn't far offshore and where even in the winter the seas are pleasant and perfectly swimable at all times outside of heavy storms. There the ocean remains usually calm and at essentially plausible bathtub temperatures (https://www.surf-forecast.com/sstgraphs/Fort-Lauderdale-14th...), even in the middle of the night every month of the year. When I first traveled to California and encountered the pacific with freezing cold waters and giant crashing waves against cliffs ... suddenly the ocean as it existed in art and literature made much more sense to me.

Experiencing an actually dark sky made the wonder at the night sky in older literature make so much more sense to me in a similar way. ... and an actually dark sky is a lot more accessible than a total eclipse too: You might have to travel a considerable distance to see either, but a clear dark sky is available on many more nights.

https://darksitefinder.com/map/

I share your sentiment. I volunteer for a charity that provides international disaster response. I was in Mozambique earlier this year, in the middle of a disaster zone, no power so no light pollution. Here's a short extract from a piece I wrote about the experience one night. I was sleeping on the concrete roof of the farmhouse that was centre of the aid distribution in the area...

-------------------------------------------

Cold. Wet. It is 0230. We've just been rained on. A light rain but it's cold and the mesh netting of the mosipod offers free passage to soak me inside. The days toll of many litres of water sits heavy within. Arise, down the steps, toilet. Back outside. Up the steps.

I look up.

The sight that greets me will stay with me forever. In the midst of disaster I see the dazzling, aching beauty of the heavens arc across the sky above. Not a single light shines on the land around me. The world is silent and utterly still save for my breath and the faint sense of life from my team mates sleeping around me.

From horizon to horizon the sky is vivid and alive with twinkle and sparkle and depth and clarity. Such light and colour as found only in the imagination is accented with an occasional shooting star. I don't know how long I stood there. I just have to stare at it all. I feel like I can reach up and touch the universe itself it's so clear above me.

I wasn't the only one. Someone else is standing out here to. In the starlight, I don't know who.

"Magnificent, isn't it?" and acknowledgement, is all we can exchange.

Somehow language just doesn't capture it. Words are just a dull tribute to the majesty the sky shared with us that night.

I lie down. Staring up at the scene above now muted by the mosquito mesh. I fall asleep to fireflies dancing above me.

--------------------------------------------

The experience, and others gained in that month I was there, will stay with me forever. There was something primal and ancient about seeing the sky I saw that night. I can truly understand our ancestors predisposition to create gods and tell the stories written in the heavens above them. It was an amazing experience.

> But people don't care

Can confirm:

https://news.ycombinator.com/item?id=21277251

A few years ago there was a heavy snowstorm in Provo Utah, that caused a very local power outage. I was able to continue reading a book using only light pollution bouncing off the clouds.

(The window I was at was facing away from the town the light was coming from)

If you want dark skies, move to the country. There's tons of trade-offs to living in an urban areas and light pollution is but one of them.

Light pollution doesn't have to be nearly as bad as it is, we're just cheap and callous people. We could have cities and still be able to see a few more stars than the half dozen you might see now. I wonder how many people have never seen the milky way? It's a great big stripe right across the sky you can see with your bare eyes, if someone could kindly turn off their giant fuckin' BUY NOW sign and point the street lights at the street instead of into the sky.

Kids don't get to choose where they move, I think they should be able to see the stars. Just one of many things we're continuing to ruin.

We subdivide so small that people don't have room to grow a single tree now, and the subdivision stretches out over the horizon. We build cities where trees aren't planted. We cover up the sky and the earth alike.

If you do manage to grow a tree, eventually they'll come tell you its now a hazard, cut it down.

Even 'in the country' there is a considerable amount of light pollution-- and per the subject of this article, there is likely to be more there in the future! :)

City vs country is seeing no stars at all or only a couple vs hundreds, but to see thousands you have to be a long way from any kind of development.

I wonder if this was less true a couple decades ago or more-- say, in the mid-1990s. I remember being out on a rural road in northern Wisconsin (about an hour north of Green Bay) where the driver of the car pulled over and turned off the car & lights so I could see the sky. In my memory, at least, there seemed to be thousands visible, along with the Milky Way.

It's less efficient to have all that light leaking to the sky. Makes sense to pass some sort of fee or regulation on massive light pollution like that. It's like methane leaks: it'd probably save some money to fix the problem, but the business deprioritizes it because the biggest cost is an externality which they do not (mostly) bear.

If there is something offensive in here, it's the use of electricity when there is a free light source around.

Since plants absorb certain wavelengths of light, and LEDs produce certain wavelengths, it can be more efficient to grow plants with solar charged LEDs than with solar directly.

The yellow/orange lights could very well be high-pressure sodium (HPS) lighting, the same type used in street lights prior to LEDs. Like the street lights, LED lights seems to have less wash and reflection back into the night sky than HPS, and use less power than HPS for the same growth effect on the plant.

The industry is still transitioning to LED lighting due to cost and because some plants don't respond very well to LED light, so more development is required.

I remember when HPS became a big thing in greenhouses and people would call the fire department at night thinking the glow meant a nearby fire.

The best part of buying a house out of town was that I never have to look out my bedroom window at night and see that ever-present hellish orange haze from the street lights ever again.

A lot of commercial lighting is switching off of HPS because of claims about LED lifetime costs based on (seemingly false) figures about durability. (E.g. drive around Los Angeles and see the dead/dying LED streetlights all over the place).

I wouldn't be surprised if HPS lightning starts becoming unavailable as a result-- this has already happened with LPS lightning, with several manufacturers shutting down fabrication.

> claims about LED lifetime costs based on (seemingly false) figures about durability. (E.g. drive around Los Angeles and see the dead/dying LED streetlights all over the place).

LED can be made durable if desired. In Detroit's case[1], the high failure rate can be attributed to manufacturer cutting corner on heat dissipation.

[1]: https://news.ycombinator.com/item?id=19848794

I think it is definitely possible. I don’t know of any led grow lights that make yellow tinged light, nor any reason they would want led lights with such a low color temperature. Double ended hps bulbs are still pretty efficient and I’m sure many greenhouses haven’t switched over. Gavita is a huge manufacturer and pioneer of lights like this and is based in the Netherlands.

Ironically, the lights in these "green" houses will be anything but green precisely for the reason that greenhouses are called that in the first place!

Most leaves are green. This is to say that green light is reflected, and it's the OTHER wavelengths that are absorbed by the chlorophyll. So you need a light that is brighter in other parts of the spectrum where the absorption is strongest. Hence, a NON-green light.

https://en.wikipedia.org/wiki/Chlorophyll

The curious thing is that sun gives most energy near green color so plants evolved to reflect the most energetic part of sun's spectrum.

And nobody knows why.

There’s speculation about this. Plants absorbing green grew too well and then the population collapsed on early earth. The survivors were mutants who didn’t absorb green.

Hence that magenta...

At least they can do the Avatar palette.

The blurple lighting ended up being substandard for growing. Although you need to match the [Chlorophyll absorption spectrum](https://upload.wikimedia.org/wikipedia/commons/f/f6/Chloroph...), it isn't the only thing in a plant that absorbs light, and the proper spectrum is closer to [this](https://supergrowled.com/wp-content/uploads/Plant-Light-Abso...).

The best performing LED grow light designs are essentially conventional full spectrum white light, sometimes boosted with additional far red, not the blurple lights that just make short unusually dense, flavorless plants.

Oh okay, I've heard similar things about netting in nethouses; any colours other than white or black lead to unwanted results (like perhaps desease).

Ahh, right, markdown doesn't work on HN. I tried.

This is absolutely beautiful. I get the clear sky argument, but personally I think there's something amazing about having a city full of these at night. Imagine seeing such a city from the ISS.

So beautiful and that's food right there.

Unfortunately the side effect of any artificial lighting in greenhouses is massive light pollution and pretty much no view of the night sky. I guess not being able to see the stars is a small price to pay for fresh vegetables year round, but having grown up far from greenhouses, I still miss the stars.

The Netherlands primarily fossil fuels to heat and light greenhouses. This industry has a large carbon footprint.

Just to give some numbers:

The Dutch greenhouse horticulture sector has emitted 6-8 megatons of CO2 per year between 2000-2015 and emissions are expected to decrease to ~4 megatons of CO2 per year in 2020 [1]. 7 megatons is approximately 4% of national emissions [2].

[1] pdf, https://www.wur.nl/upload_mm/c/e/c/f827af2c-9ae6-4bb5-bb47-9...

[2] https://www.cbs.nl/nl-nl/nieuws/2018/37/co2-uitstoot-in-2017...

4% of national emissions is a lot considering the purpose here, and taking into account, as said, that the Netherlands emit quite a bit to begin with because of fossil fuels use (Wikipedia says they emitted twice as much as France per capita in 2014 [1], for example)

[1] https://en.m.wikipedia.org/wiki/List_of_countries_by_carbon_...

> 7 megatons is approximately 4% of national emissions

What makes up the bulk of national emissions?

As of 2nd quarter 2019 [1] rougly:

32% Energy, water and waste services

24.5% Agriculture, mining, industry, construction

12% Other services

13.5% Transport

18% Households

This is a major challenge (not only in the Netherlands) because it appears there is no one "bulk emitter" that must be tackled.

[1] https://www.cbs.nl/nl-nl/nieuws/2019/39/uitstoot-co2-hoger-i...

Maybe they should just pump that CO2 into the greenhouses!

They do. But more commonly, CO2 is intentionally produced in greenhouses by burning natural gas (or propane) for no other reason than to create CO2 for the benefit of the plants:

https://dutchgreenhouses.com/technology/co2-enrichment

I get that greenhouse windows have to be transparent during the day to let in the sun - so why don’t they add shutters that close at sundown and preserve even more of the LED light inside the greenhouses, reducing the necessary power input and solving the light pollution problem?

Because it’s cheaper to make the lights brighter than the reflective shutter system you are imagining

How does making lights brighter save the problem?

Use to be farms in the middle of nowhere was where you could get away from the orange and yellow glows of the city streets. Massive farms that glow too?

I've been reading a Sci-Fi series recently where one human sees a world totally dark at night except for a few human settlements .. and the character thinks about what Earth must have been like from orbit, before humanity arose.

Seems like this could have been better done in Iceland with access to lots of heat and power from renewable sources.

They do: https://nea.is/geothermal/direct-utilization/greenhouses/

My first thought was how much energy they are squandering.

Guessing the glass roof to collect sunlight in the day.

Seems like merely rolling out mirrored mylar (horizontal) curtains at night would be worth it in energy cost savings alone, and of course create the benefit of minimizing light pollution.

Strangely beautiful, but also scary... makes you wonder what people will come up with once nuclear fusion makes electric energy even cheaper - I guess the amount of light pollution we have today will pale by comparison (no pun intended).

I’m curious if there is any kind of post-processing being done to these pictures. They are beautiful in a strange way

This is a mark of inefficiency, no?

How is this inefficient?

The light should be going to the plants, not space?

Look at the sides of the greenhouses, which are far brighter than the roofs. The light from the roof is only what's reflected off the plants. LEDs are quite directional.

By definition, all the light you can see is light that isn't going to the plants - light reflected off the plants could still be redirected, right?