Purple light means go, ultraviolet light means stop

Controlling a membrane’s permeability using different colors of light.

Controlling a membrane’s permeability with light is preferable to controlling it with heat or electricity – two readily used alternative methods – for several reasons, Glowacki said. For starters, light can operate remotely. Instead of attaching electrical lines to the membrane, a lamp or a laser can be directed at the membrane from a distance. This could allow engineers to make much smaller, simpler setups.

Another advantage is that the color of the light illuminating the membrane can be changed precisely and almost instantaneously. Other methods, like heating and cooling, take a relatively long time and repeated heating and cooling can damage the membrane.