Evaporation can also occur with just light (Credit: MIT.edu/ CC-BY-SA-2.0)

Evaporation has long been thought to happen only when a liquid absorbs enough heat to turn into vapor. However, researchers at the Massachusetts Institute of Technology (MIT) recently found the process can also occur in the presence of just light.

Study leader Gang Chen and his team stumbled upon the discovery accidentally. The water in their experiments, held by a sponge-like material called hydrogel, was evaporating at a higher rate than could be explained by the amount of heat it was getting. This led them to wonder if something else was contributing to the water loss.

Water being evaporated out of a hydrogel under a green light (Credit: MIT.edu/ CC-BY-SA-2.0)

After conducting numerous experiments, the team reached a stunning conclusion. They found that under certain conditions, light alone can cause evaporation. No heat was needed!

To confirm their theory, the researchers exposed water-soaked hydrogels to various light colors. This time, they measured the rate of evaporation. To their surprise, they found it differed depending on the color's wavelength. Green, whose wavelength falls in the middle of the visible light spectrum, was the most effective. It was able to evaporate water three times faster than other colors. The researchers called the light-induced evaporation process the "photomolecular effect."

Green was the most efficient at evaporating water (Credit: Philip Ronan/ CC BY-SA-3.0/ Commons.wikimedia.org)

The MIT team revealed their findings in the Proceedings of the National Academy of Sciences on November 7, 2023. They believe the phenomenon could be happening in everyday environments, such as water within soils or ocean surfaces. The researchers now plan to investigate if light evaporation impacts climate change.

Resources: news.mit.edu, livescience.com