Your phone screen may soon be able to detect the shadow of your hand, responding to touchless gestures. Scientists have discovered a way to create light-emitting diodes (LEDs) that can also detect and absorb light. The researchers modified tiny versions of LEDs, called quantum dots. Normally, semiconductor material insulates a quantum dot within a shell, preventing it from detecting light. To solve that problem, scientists have created “nanorods” in which quantum dots directly contact two semiconductor materials. One allows movement of positive charge, and the other allows movement of negative charge (see above). Together, these materials can regulate movement of electrons into and out of the quantum dot, allowing it to both emit and detect light, scientists report today in Science. These two-way LEDs switch between light-emitting and light-detecting modes so rapidly that the human eye sees only constant red light. The researchers are now moving toward developing green and blue versions of the two-way LEDs for multicolored displays. This could open new possibilities for device interfaces and applications, the researchers say, including screens that harvest light to charge devices, read information from other screens, or correct brightness on a pixel-by-pixel basis.