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Comment by amatecha | Hacker News Reader

Ah yeah, in the post's first "unknown light pollution" example, I figured it must be a greenhouse. I was driving through a relatively small town one time and was a bit freaked out by this ominous yellow glow off in the distance. Like, the whole sky was glowing [0]. I ended up driving out to try to find the source, and discovered it was a huge greenhouse/farm. Luckily not an extraterrestrial landing zone or so on ;)

[0] looked like this https://i.cbc.ca/1.4925044.1543460834!/fileImage/httpImage/i...

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They are absolutely awful.

I've lived relatively close to one and hadn't seen night's sky for the whole duration I stayed there. Actually the whole town's sky was filled with light polution from one cucumber farm.

They also tend to generate a ton of RF noise if not properly filtered.

I was having problems with my cable internet periodically dropping out for a few minutes at a time, it took them two or three tries, and every time the support guy came out they were very careful to tell me that "your neighbors grow lights may cause that when they switch on at some particular time every night". So I guess they do put out quite a bit of RF noise ;)

("of course, it's company policy never to imply ownership in the event of a dildo.")

Think it was a firmware bug in the modem, because the modem never realized it was offline or showed a connectivity disruption on the street. Luckily it dropped off one time while I was on the phone with a tech. They were using a new Charter Spectrum branded modem and as soon as they swapped to an Arris it stopped happening.

Grow lights are pretty notorious.

http://www.arrl.org/grow-light-rfi

"even under the best of circumstances, the importance of diplomacy cannot be overemphasized during these discussions"

Yellow glow is understandable, but check out this purple one

https://www.cbc.ca/news/canada/windsor/not-northern-lights-g...

Ah yeah, that's exactly where I got the above photo from. The purple glow is ridiculous! At least the yellow is a little less "abrasive" and more natural-looking.

Purple makes sense. Blue and red are the colors of light that are most effectively absorbed by chlorophyll-pigmented plant leaves. Yellow would be a lot less efficient because more would reflect off the green leaves.

Magenta is the complementary (opposite) color of green.

I wonder how much money might be saved just by installing shutters to reflect the light (and heat) back into the greenhouse instead of letting it pollute everywhere.

Light perception is logarithmic. There might well be 99% of the light hitting the plants leaves, and 1% escaping to the environment, yet that 1% will only appear a bit dimmer than the original light source.

That's fine, but I'm still curious about the costs involved.

Here's an article[0] that mentions a containment product. Its a fire-resistant white polyester screen.

Some of the challenges include excess heat (HPS emit ~80% as heat) and moisture.

I haven't found anything that breaks down the costs. It seems the primary motivation is bylaw compliance.

[0] https://gpnmag.com/article/cleaning-light-pollution/

> She said the municipality is trying to find the best way to address the issue, while still considering the economic side.

Just make them put tarps over the greenhouses!?

Don't want to run the lights in the day.

Take them off during the daytime. They're not permanent installments.

Those greenhouses are the size of many football fields.. Putting tarps over them is a job that will take many days :)

But yeah shutters or something smarter (like two-state glass) should work IMO. I think you even get glass that can switch to mirror mode.

> like two-state glass

That would be crazy-expensive. A lot of greenhouses use poly-film, to give you an idea of the budget. Replacement cost is a large factor.

There is research on whether solar arrays would be a net benefit. Those cells would catch most of the sun’s light, turn it into electricity to power the LEDs that have wave lengths that are better matched to what the plants need.

A variation of that only catches the sun’s green light and uses it to power pink/red LEDs (https://www.treehugger.com/solar-technology/solar-smart-gree...)

Mass produced photovoltaic is 22% efficient. LEDs tuned to the plant are 50% efficient. Net efficiency 11%. Now you need 9 times as much land to grow the same number of plants.

Plants reject a lot of the visible spectrum. The question is, can you make up for the losses in solar panels by giving plants light that they can use more efficiently?

Probably expensive and still a waste of electricity, but why not automate it like the covers over pro-tennis courts?

LED grow lights. Apparently the plants only need red and blue light. That purple is the glow of more efficiently wasting electricity.

Photo caption says LED. That color is common for them, or even a mix of blue and red. When going LED they only use ones with the wavelengths the plants actually use. You also see this in articles covering vertical farming prototypes. And when i think about it, this is nothing new, because i remember people growing exotic plants in their windows in not so exotic germany, often had 'plant-lights' with that purple sheen to support growth. That was decades ago, done with flourescent tubes. Nowadays it looks like this:

https://en.wikipedia.org/wiki/File:LED_panel_and_plants.jpg https://en.wikipedia.org/wiki/File:Led_grown_lights_useful.j...

I bought some of these dedicated wave length LED grow lights once winter. The color is so off-putting that I built a grow tent around them. Event the cats quit using that part of the house before I made the tent. However, the plants sure loved them. I had a couple of potted citrus trees that started blossoming after a couple of weeks inside under these lights. The house smelled amazing. Wasn't worth the loss of square footage in the house though.

I would have changed the lights.

There you go again using logic. Besides, I had to at least let the lights work long enough to see if they worked. In the end they did. They're just not friendly for home living aesthetics.

> When going LED they only use ones with the wavelengths the plants actually use.

And those wavelengths are...everything except green. You can tell this because plants are green, because they reflect green light and absorb everything else. So an LED-lit greenhouse looks "anti-green", which is some kind of reddish purple. It's a bit more complicated than this in practice, but not much.

I wonder why don't they use mirrors to reflect the light back at night time.

Metallized PETF film is strong enough, very lightweight, and not expensive, while reflecting, say, 95% of the light.

Could save them a lot in electric bills.

Maybe it's to do with having to peel it back during the day? Should be quite an increase of mechanical complexity compared to just switching the lights on and off

Pulling a shroud over the roof at night is standard practice in passive greenhouses in China. It dramatically reduces heating costs. I’d guess it would reduce lighting costs as well.

Anyway, the necessary mechanical systems exist and are produced/deployed at scale.

Maybe US regulators should step in and require light / heat shielding at night above a certain size.

https://s1.15min.lt/images/photos/2019/11/05/original/aa_201...

How it looks like from bird's eye view at daytime.

It looks even more amazing when it's cloudy and the ground is covered by snow. You can go skiing in the forest at night and you won't need any additional lights.

I got the train from Hanoi to Ho Chi Minh city last year - the length of Vietnam.

I was struck by the phenomenal degree of light pollution the dragonfruit plantations made - huge arrays of incredibly bright lights, illuminating the sky and area for miles around them in a brighter than moonlight glow.

Similarly, while at sea in the Andaman and gulf of Thailand, the entire horizon is dotted with the bright sparks of squid boats, which use huge lighting arrays as artificial moons to attract squid.

Between the smog and light pollution, it’s a wonder there’s any night sky at all in SE Asia.

These greenhouses and all the complicated local politics that go along with them are the subject of a great episode of Outside/In:

http://outsideinradio.org/shows/ep45

It does make you wonder if it's not just moths attracted to strange lights at night.

Iconic scene in "Saving Grace":

https://www.youtube.com/watch?v=3eMYxkEtxlM

Same thing happened to me -- some greenhouses off highway one near Half Moon Bay

That could be the place that has https://www.ouroborosfarms.com/

Interesting aquaponics greenhouse. Worth a visit.

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