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What are the mysterious light sources on light pollution maps?

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Re: What are the mysterious light sources on light pollution maps?

#61

Post by BurningFrog »

tzs wrote: post #60

The map of the United States raises an interesting question. There is a pretty distinct line down the middle, with nearly opposite light/dark patterns on different sides of the line. To the east, it is mostly bright areas with islands of dark. To the west, it is mostly dark areas with islands of bright. If you look at a regular map, nothing really stands out to explain the difference. It is not like there is, say, a…

Yeah, there is a pretty distinct line from Winnipeg to San Antonio, separating light from dark.

If you look at a population density map, it looks quite similar: http://dafi1637.blogspot.com/2017/10/united-states-populatio...

I think that explains the immediate effect. You can of course then wonder why the population is distributed that way, but I feel I've done enough here :)

Re: What are the mysterious light sources on light pollution maps?

#62

Post by vvanders »

kabacha wrote: post #58
amatecha wrote: post #8

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 ;) […

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.

Re: What are the mysterious light sources on light pollution maps?

#63

Post by c3534l »

derefr wrote: post #2

One thing I'd like to see is a light-pollution map of the US overlaid with a map of all US federal land. To answer the question: what's the brightest thing the federal government is doing?

> what's the brightest thing the federal government is doing?

There's a cynical joke in there somewhere.

Re: What are the mysterious light sources on light pollution maps?

#64

Post by duderific »

tzs wrote: post #60

The map of the United States raises an interesting question. There is a pretty distinct line down the middle, with nearly opposite light/dark patterns on different sides of the line. To the east, it is mostly bright areas with islands of dark. To the west, it is mostly dark areas with islands of bright. If you look at a regular map, nothing really stands out to explain the difference. It is not like there is, say, a…

My guess would be that the land is not as conducive to farming west of that line, both in terms of soil and weather. So early settlements didn't occur there, and thus cities did not emerge from those areas.

The cities that did evolve in the West were based on different resources: ports around the ocean, mining, oil, railroad stops etc.

Re: What are the mysterious light sources on light pollution maps?

#65

Post by TrumpMyGuns »

ficklepickle wrote: post #52
yread wrote: post #12

Earlier quoted context omitted.

Yellow glow is understandable, but check out this purple one https://www.cbc.ca/news/canada/windsor/not-northern-lights-g...

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

Wasting? God, this site is full of bubble-boy dolts.

Re: What are the mysterious light sources on light pollution maps?

#66

Post by coderintherye »

crazygringo wrote: post #50
robbrown451 wrote: post #43

You'd think they'd do better at containing the light from the grow houses, so more ends up on the plants and less making it to space. Like, foil or something?

Since these are greenhouses they have to be clear to let the light in during the day, I assume. Anything that's going to reflect light to prevent it from leaving at night will also block the sun from hitting the leaves during the day, unless it's a complicated mechanical system that can be folded up during the daytime. I'm guessing such a reliable mechnical system together with maintenance is much more expensive than…

There are systems on the market that are not too complicated. We have an iGrow system for instance for our greenhouse.

But yes, the covers do tend to snag and such when rolling up and that can be problematic and require maintenance. Definitely though the industry does not seem to have yet embraced automation much.

Re: What are the mysterious light sources on light pollution maps?

#67

Post by maxerickson »

3JPLW wrote: post #13
twic wrote: post #6

I flew through the night to Singapore once. I remember two very striking light sources. Firstly, oil well flares in the Middle East. The oil fields are in the middle of nowhere, so they're these huge orange-red blooms set in utter darkness. Secondly, Delhi. The city is brightly lit with streetlights. But there's a suburb (?) to the south, Faridabad, that's as brightly lit, but with a different, whiter, kind of lights…

Chicago has been slowly replacing its yellow sodium streetlamps with efficient LEDs that project down instead of up. They've been working block-by-block in a systematic way that you can see when you fly into the city at night. It's quite dramatic.

My town replaced the sodium light across the street with a LED. A lot more light comes in the windows now. It sucks.

Re: What are the mysterious light sources on light pollution maps?

#68

Post by dylan604 »

LargoLasskhyfv wrote: post #53
yread wrote: post #12

Earlier quoted context omitted.

Yellow glow is understandable, but check out this purple one https://www.cbc.ca/news/canada/windsor/not-northern-lights-g...

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…

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.

Re: What are the mysterious light sources on light pollution maps?

#69

Post by nine_k »

amatecha wrote: post #8

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 ;) […

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.

Re: What are the mysterious light sources on light pollution maps?

#70

Post by dmurray »

LargoLasskhyfv wrote: post #53
yread wrote: post #12

Earlier quoted context omitted.

Yellow glow is understandable, but check out this purple one https://www.cbc.ca/news/canada/windsor/not-northern-lights-g...

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…

> 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.

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