What Is Forward Voltage In An LED And Does It Vary For Different Colours?

Light emitting diode, abbreviated as LED, is an integral part of emergency lighting systems in most public services vehicles such as police cars, ambulances, fire trucks and more. They are even used in traffic arrows mounted on the back of utility trucks. There are many ways to select a LED, such as a lumen rating, IP rating, junction temperature and more. Another such factor to consider is the forward voltage. Its definition and importance will be addressed below. 

What is forward voltage?

In essence, a forward voltage can be defined as the voltage used by the LED light when a forward current passes through it. It is denoted by VF. It is an essential parameter as the light has to meet this voltage requirement to be functional.

Does forward voltage vary according to light colours?

The answer is yes, the forward voltage will vary for different light colours. However, the reason behind this variation is rather simple. The manufacturers use different materials to create LEDs with different colours. Here are a few examples: 

- To emit blue light in an LED, manufacturers use Indium Gallium Nitride (InGaN) and Silicon Carbide (SiC). To generate the light, the materials release electrons that travel across the LED, and the energy they emit is of the desired colour and wavelength. Therefore in this case, when current passes through the LED, a blue light of around 450-500 nm is released. Its forward voltage is around 2.5 to 3.7.

- To emit red light in an LED, manufacturers use Aluminum Gallium Arsenide (AlGaAs) and Gallium arsenide phosphide (GaAsP). While the process of electrons releasing energy is the same, the wavelength is quite different in this case, around 610-760 nm. Consequently, the forward voltage is also drastically different, around 1.6 to 2.0.

To Conclude

To sum it up, depending on the light spectrum, the forward voltage will also change, as will the materials used in the LED. This also has to be taken into consideration along with junction temperature, lumen rating and IP rating. 

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