The limiting factor in mobile devices is the energy that can be extracted from a battery.
- Smartphone batteries are limited by the energy that they can hold from 100% charge until the voltage drops to a level that will no support the functions of the phone.
- Typically, the forward voltage of an LED is between 1.8 and 3.3 volts. It varies by the color of the LED. A red LED typically drops around 1.7 to 2.0 volts, but since both voltage drop and light frequency increase with band gap, a blue LED may drop around 3 to 3.3 volts. Blue light is needed for the light used to enable the camera.