What kind of displays can I use effectively with a coin cell battery (CR2450)? The backlight or the entire display would be on only when necessary. From previous answers I know that a liquid crystal display without backlight can be used but I wanted to know if there is some kind of display with good visibility at night. Is there some kind of "ultra-low-power" display with good visibility at night?
LCD display with a tritium backlight (half-life ~12 years) should be possible. The tritium emits beta particles that can excite phosphors to emit visible light. Glass is typically used to contain the tritium gas.
Watches have been made incorporating this principle, some Ball watches currently use tritium capsules for analog dial illumination, and there is at least one company claiming to offer micro-capsules.
Don't expect spectacular brightness, even nuclear-powered illumination has its limits.