ePaper displays are reflective, meaning that they leverage the ambient light in the environment for viewing - just like paper.

And just like paper, when there is little or no light around you, a front light can be used for dim light viewing. 

Many of E Ink's customers design in a front light solution to their device. A front light uses a very thin light guide material to uniformly disperse light over the surface of the display. The light source is usually in the form of LEDs mounted in the sides of the display module. Unlike the backlights contained in LCDs and OLEDs, where the light is emitted through the display and towards your eyes, front lights do not shine directly into your eyes. The light is angled down the surface of the display, and the reflected light allows you to view the display content. 

E Ink can manufacture the entire display module including the front light.

E Ink ComfortGaze™ is a new front light technology designed by E Ink's front light team of engineers. ComfortGaze has been engineered to reduce the amount of blue light reflected off the surface of the display, providing further comfort while reading. ComfortGaze has reduced the Blue Light Ratio (BLR) and Blue Light Toxicity Factor (BLTF) by up to 60 percent and 24 percent respectively compared to the previous generation of front light designs.