Hacker News Reader

Comment by yread | Hacker News Reader

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 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 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/

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.

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.

> 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.

Reply on news.ycombinator.com