The additional size options give product and service designers more flexibility when choosing displays, typically for use cases where there is no access to mains power. Unlike conventional TFT LCDs, e-paper displays only consume energy when you change what’s on the display, so maintaining a static image requires no energy at all. And because each screen update uses relatively little energy, e-paper displays can be powered using either a small battery or harvested energy.
With state-of-the-art driving waveform and respective pixel densities of 130 dpi (3.7-inch) and 117 dpi (4.37-inch), both can render sharp and detailed images and text. Because Pervasive Displays pre-programs key capabilities into the displays, they can be driven without consuming resource from the host controller.
Pervasive Displays - www.pervasivedisplays.com