
The Ever-Present Glow of LED Greenhouses - jweir
https://www.thisiscolossal.com/2019/10/greenhouse-series/
======
tzs
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.

~~~
the8472
At least for greenhouses it might be simpler to require narrow-band LEDs and
matching narrow-band filter glasses.

~~~
e12e
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?)

~~~
the8472
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.

~~~
e12e
I suppose you could always go for semi-transparent - so not reflect but absorb
a fraction of the light?

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latchkey
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://www.growables.org/information/TropicalFruit/DragonFruitSubTropicalQldClub.htm)

[https://english.vietnamnet.vn/fms/science-
it/187197/vietname...](https://english.vietnamnet.vn/fms/science-
it/187197/vietnamese-scientists-invent-light-to-control-plant-flowering.html)

~~~
peter_d_sherman
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."

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

~~~
PostOnce
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.

~~~
nullc
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.

~~~
chrisco255
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.

~~~
nullc
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.

~~~
slfnflctd
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.

------
foofoo55
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.

~~~
nullc
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.

~~~
curben
> 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](https://news.ycombinator.com/item?id=19848794)

------
pure-awesome
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](https://en.wikipedia.org/wiki/Chlorophyll)

~~~
scotty79
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.

~~~
zeckalpha
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.

------
johnmorrison
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.

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starrio
So beautiful and that's food right there.

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micheljansen
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.

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

~~~
itcrowd
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...](https://www.wur.nl/upload_mm/c/e/c/f827af2c-9ae6-4bb5-bb47-920f4700cef8_2016-067%20Velden_rapport_def.pdf)

[2] [https://www.cbs.nl/nl-nl/nieuws/2018/37/co2-uitstoot-
in-2017...](https://www.cbs.nl/nl-nl/nieuws/2018/37/co2-uitstoot-
in-2017-gelijk-aan-die-in-1990)

~~~
MuffinFlavored
> 7 megatons is approximately 4% of national emissions

What makes up the bulk of national emissions?

~~~
itcrowd
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...](https://www.cbs.nl/nl-nl/nieuws/2019/39/uitstoot-co2-hoger-in-
het-tweede-kwartaal-van-2019)

------
manmal
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?

~~~
dean177
Because it’s cheaper to make the lights brighter than the reflective shutter
system you are imagining

~~~
manmal
How does making lights brighter save the problem?

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djsumdog
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.

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

~~~
zeckalpha
They do: [https://nea.is/geothermal/direct-
utilization/greenhouses/](https://nea.is/geothermal/direct-
utilization/greenhouses/)

------
toss1
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.

------
rob74
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).

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

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exabrial
This is a mark of inefficiency, no?

~~~
stordoff
How is this inefficient?

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

~~~
Animats
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.

~~~
joe_the_user
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?

