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In a surprising finding, light can make water evaporate without heat

https://news.mit.edu/2023/surprising-finding-light-makes-water-evaporate-without-heat-1031

At the interface of water and air, light can, in certain conditions, bring about evaporation without the need for heat, according to an MIT study.

In a surprising finding, light can make water evaporate without heat::At the interface of water and air, light can, in certain conditions, bring about evaporation without the need for heat, according to an MIT study.

15 comments

Gork

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Fascinating. It peaks at green wavelengths.

Plants are green.

I don't know where I'm going with this but it sounds cool.

sharkfucker420

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Plants are green specifically because the red and blue wavelengths of light are useful for breaking specific chemical bonds necessary for photosynthesis and as such are readily absorbed by the plant. The plant makes efficient use of the energy provided by only absorbing the wavelengths necessary for its processes. However, plants still absorb 90% of green light and green light holds the highest proportion of the energy radiated by the sun.

To be more clear, green light has too much energy. When plants absorb light it first enters a protein mesh containing pigments such as chlorophyll that function like an antenna or receiver for a range of wavelengths. The pigments then transfer the energy to a "reaction center" where it turns this electromagnetic energy into chemical energy (photosynthesis). This process is exceedingly efficient; almost all of the absorbed energy is converted into electrons the plants can use. However, this protein mesh antenna is not solid and is constantly moving. These movements affect how energy is absorbed and how it flows through the pigments. Think of diffraction in water. Fluctuation in the intensity of light can create noise in this process; a quick brush of shade or sudden increase of light intensity can decrease the efficiency of photosynthesis. For plants and really everything that lives, a steady input and output of energy is desirable. Not enough electrons making it to the reaction center causes energy failure while too much will cause general overcharging effects that can damage tissue. When the noise of this system fluctuates it makes it difficult for the plant to self regulate it's energy flow and could cause the plant to kill it's own tissue or essentially starve. So essentially, while absorbing all green light would provide the plant with more energy, it's not capable of handling this energy so plants evolved to limit their intake of green light.

However, this is not to say that green lights ability to efficiently evaporate water is not a factor in this evolutionary development, hell it's probable that these two things are heavily related. Green light might evaporate water so well because of some combination of its relatively high energy mixed with the size of its wavelength interacting with the hydrogen bonds between water molecules in a more efficient manner than other wavelengths of electromagnetic radiation.

source for those interested

Lord_ToRA

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Thanks, Sharkfucker420

sharkfucker420

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Always happy to provide walls of text about things I only just learned quite recently. I'm sure I oversimplified something or other in a way that makes it technically incorrect or honestly I could have gotten something completely wrong so I added my source to the bottom.

abhibeckert

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Not a correction but a minor clarification. Green light doesn't inherently have the most energy. Shorter wavelengths have more energy but tend to scatter in our atmosphere and a lot of it doesn't reach the surface (that's why the sky is blue).

It's also why UV light causes skin cancer and burns on humans, and kills bacteria/viruses/etc. Green is also pretty poor at lighting up flourescents, while blue(which has more energy) does much better. Ultra violet is even better than blue.

That does make me question your theory that green light is the most effective at evaporating water because it's high energy. Blue/violet/ultra violet would be better than green if that was the case. The test didn't use sunlight, it used artificial lighting and the effects of the atmosphere are effectively zero over short distances.

sharkfucker420

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Yeah I should've been more clear about that. I'm currently getting my BS in physics so I'm more than aware of how energy correlates with the frequency/wavelength of electromagnetic radiation.

I'm under the assumption that there is some key information I'm missing regarding how energy is transferred to water from the electromagnetic radiation that makes green light carry more effective or usable energy for breaking those intramolecular bonds. Perhaps it's the sepcific size of the wavelength? I know that often times when an objects size matches the wavelength passing through them some interesting things can happen though I don't know details on this subject so I can't be certain here.

In the case of plants the green light only carries more effective energy because the sun releases so much of it. Blue light carries more energy but green light is released so much more that it's share of the percentage of total energy released by the sun is much greater. So when sunlight fluctuates for one reason or another it's easier for the plant to regulate it's own energy if it blocks out some of that green light.

I'll amend that in my original comment

abhibeckert

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No worries. I did learn a lot from your comment by the way as I'm by no means a physics person... I just work with light as part of my job and the different behaviour from one colour/wavelength has practical (and safety) implications that I have to account for.

sharkfucker420

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Thanksnfor the clarification, I wouldn't have fixed that otherwise. It's 5 am where I am and I haven't slept so I'm not surprised I made that sort of mistake.

What do you do for work?

LukeMedia

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I love you, thanks for the fun fact, SharkFucker420!

MonkderZweite

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Wasn't there something sometime about how plants would look if we had a red dwarf instead? They would look blackish, because more infrared.

webghost0101

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Literally yesterday i pitched to my wife that i cant wait till i have some personal drone that ca evaporate and deflect raindrops before they fall on me. Essentially creating a flying rain shield.

Did not expect to be a step closer today already.

pastermil

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Cool idea, but I'll just go with umbrella.

Rootiest

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Eventually when the cool factor of light umbrellas wears off, traditional retro umbrellas will become cool again. But you can't beat the convenience of light-based rain protection

Master

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The reverse pink panther.

andrewrgross

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I'm too exhausted to read the article, but that headline in bonkers.