LEDs

LEDs tend to be used in one of two ways: either for indication or illumination.

Indicator LEDs are low power, cheap LEDs that don’t emit much light. For example, LEDs used to indicate that power is plugged in, or that a battery is charged. You can use high output LEDs and put less current through them (by using a larger series resistor)

Illumination LEDs are high power, more expensive and can be used to actually light something up. For example, LED headlamps, bike lights, christmas tree lights, etc.