严格实验表明可见光不会加速水蒸发

In recent experiments involving hydrogels and water droplets, researchers have proposed that exposure to visible light could make water evaporate faster without heating it. However, direct evidence that light acts on water itself has proven elusive.

Through new research published in PNAS, Mischa Bonn and colleagues at the Max Planck Institute for Polymer Research in Mainz, Germany, have put the idea through a rigorous series of tests. They found that visible light has no measurable effect on the evaporation of pure water—hinting at an alternative influence on the evaporation rate that has yet to be discovered.

Unexplained evaporation

In previous experiments, researchers investigated the impact of visible light exposure on water-soaked gels called hydrogels, as well as tiny water droplets. Surprisingly, the water in these samples seemed to evaporate more quickly than could be explained by warming alone.

One possible explanation was that light could be directly knocking water molecules free from the surface, a process dubbed the "photomolecular effect." If this were the case, it could change how scientists model water loss from oceans and clouds, and could lead to new solar-powered systems for purifying water.

However, important questions remained about whether light was really acting on the water molecules themselves or if the results came from the materials and measuring techniques being used.

Rigorous experiments

To answer these questions, Bonn's team used blue, green and red lasers to illuminate a flat surface of pure water at brightnesses similar to sunlight and over a range of humidities. With a highly precise sensor, they tracked how quickly the water's surface sank as it evaporated, comparing periods with the light on and off.

At the same time, they used a technique that detects the vibrations of molecules in just the top two or three layers of water. This would reveal whether light was loosening the bonds holding these molecules together.

Finally, they hit the surface with extremely short laser pulses, each lasting around a trillionth of a second. These pulses reached peak brightnesses more than 10 billion times higher than conventional lasers but were too brief to heat the water.

Looking for other explanations

In each case, evidence for light-driven evaporation came up short. The water's surface sank at exactly the same rate whether the light was on or off, and the vibrations of the surface molecules were unchanged. Even the intense pulses left the bonds between surface molecules undisturbed.

The result means that the fast evaporation seen in earlier experiments needs a different explanation. Bonn's team points to several possibilities: gels absorbing light and warming up, heat spreading through these materials, water vapor gathering near the surface, the gentle push of light itself, and the shapes of droplets and gel pores.

For now, their measurements offer a clear benchmark for future studies and could help engineers designing light-powered water technologies better understand where any gains are really coming from.

Written for you by our author Sam Jarman, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

Publication details

Yucong Chen et al, Visible light leaves evaporation and interfacial structure of neat water unchanged at the air–water interface, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2615377123

Who's behind this story?

Sam Jarman

Science X contributing writer; covers astrophysics, novel materials, medical imaging, and bio-inspired tech. Full profile →

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →

Robert Egan

Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

© 2026 Science X Network

Citation: Visible light does not speed up water evaporation, rigorous experiments suggest (2026, October 3) retrieved 17 October 2026 from https://phys.org/news/2026-10-visible-evaporation-rigorous.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.