Light-Emitting Diodes are circuit components that turn electricity into light. They are a type of diode, which is a circuit component that only lets current flow in one direction.

Also known as LEDs, light-emitting diodes are used as circuit indicators to let us know if something is powered on or maybe if something is wrong. When grouped together LEDs can be used to display images, like in computer monitors and TVs.

Light-Emitting Diode schematic symbol

The schematic symbol for an LED is a triangle with arrows coming off of it pointing toward a line. The arrows represent the light-emitting behavior of the component.

The triangle pointing to the line represents the direction the current will flow. Current flows into the LED from the positive terminal and exits the negative terminal.

When including LEDs in a circuit we must provide it with a specific voltage and current. These two attributes are known as forward voltage and forward current.

Forward Voltage (Vf)

An LED is a load that requires voltage provided by the voltage source. In most cases, the LED can not have the entire source voltage applied to it or it will be damaged.

Forward voltage, represented by Vf, is the optimum voltage that should be applied to an LED. Going under this voltage by too much will result in reduced current and poor illumination (or none at all). Going over the forward voltage by too much will damage the LED.

Forward Current (If)

When the forward voltage is met, the current that goes through the LED is known as the forward current, represented by If. This value is used to help design the circuit for optimum LED operation.


Use the arrows to scroll through the explanations of forward voltage (Vf) and forward current (If).

Move to the next exercise when ready.

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