Many electronic reader apps such as iBooks, Kindle, and Instapaper offer a night-time reading mode that allows easier reading in low-light conditions. The night mode simply reverses the default white background and black text to a black background with white text. This creates less strain on your eyes when reading in a dark or dimly lit environment.
Night mode can be a handy feature, but not all apps have this functionality. Luckily, the iPad and iPhone have a capability similar to night mode that can be applied to any app.