https://phys.org/news/2018-05-material-mechanical-dark.html

"The influence of complete darkness on the mechanical properties of inorganic semiconductors had not previously been investigated," study co-author Atsutomo Nakamura says. "We found that ZnS crystals in complete darkness displayed much higher plasticity than those under light exposure."

The ZnS crystals in the dark deformed plastically without fracture until a large strain of 45%. The team attributed the increased plasticity of the ZnS crystals in the dark to the high mobility of dislocations in complete darkness. Dislocations are a type of defect found in crystals and are known to influence crystal properties. Under light exposure, the ZnS crystals were brittle because their deformation mechanism was different from that in the dark.