Reflective displays are based on technology that reflects ambient light rather than emitting it.
This enables displays that can be read as easily as paper in sunlight for a more natural viewing experience, resting our eyes from the current dominance of intense backlit and emissive displays like LCD and OLED.
Recent research (read here) has shown that evening use of light-emitting devices negatively affect sleep, circadian timing and next-morning alertness. Reflective displays which can use natural ambient light or room lights provide a completely different approach to delivering the information and entertainment we seek.
This reflective viewing mode is very energy efficient, enabling devices that are unconstrained by hard-wired mains power or excessive battery drain. SRD® technology can even act in no-energy mode when displaying a static colour image!