The familiar CRT monitors or backlit LCD screens on our desks continuously consume power in order to hold an image. Electronic paper (e-paper) is different: power is only needed to change the image. Just like paper, e-paper is able to hold the image permanently without consuming any power. Displays using CRT, backlit LCD, plasma and OLED technologies are all emissive, meaning that they have to produce the photons that reach the eye. This implies that they have to compete in brightness with ambient lighting, which can result in eye strain. E-paper is the opposite: it is reflective, which makes it possible to read the display using ambient light even in the brightness of a hot sunny day.