LED Characteristics & Colours

- summary of different LED characteristics - colour, voltage drop, intensity, etc arising from the different materials and fabrication technologies used.

There is a wide variety of different LEDs available on the market. The different LED characteristics include colours light / radiation wavelength, light intensity, and a variety of other LED characteristics.

The different LED characteristics have been brought about by a variety of factors, in the manufacture of the LED. The semiconductor make-up is a factor, but fabrication technology and encapsulation also play major part of the determination of the LED characteristics.


LED colours

One of the major characteristics of an LED is its colour. Initially LED colours were very restricted. For the first years only red LEDs were available.

However as semiconductor processes were improved and new research was undertaken to investigate new materials for LEDs, different colours became available.

The diagram below shows some typical approximate curves for the voltages that may be expected for different LED colours.

Typical LED voltage curves
Typical (approximate) LED voltage curves


LED voltage drops

The voltage drop across an LED is different to that of a normal silicon LED. Typically the LED voltage drop is between around 2 and 4 volts.

The actual LED voltage that appears across the two terminals is dependent mainly upon the type of LED in question - the materials used.

As would be expected the LED voltage curve broadly follows that which would be expected for the forward characteristic for a diode. However once the diode has turned on, the voltage is relatively flat for a variety of forward current levels. This means that in some cases designers have used them as very rough voltage stabilisers - zener diodes do not operate at voltages as low as LEDs. However their performance is obviously nowhere near as good.


Summary of LED characteristics


Wavelength
Range (nm)
Colour VF @ 20mA Material
< 400 Ultraviolet 3.1 - 4.4 Aluminium nitride (AlN)
Aluminium gallium nitride (AlGaN)
Aluminium gallium indium nitride (AlGaInN)
400 - 450 Violet 2.8 - 4.0 Indium gallium nitride (InGaN)
450 - 500 Blue 2.5 - 3.7 Indium gallium nitride (InGaN)
Silicon carbide (SiC)
500 - 570 Green 1.9 - 4.0 Gallium phosphide (GaP)
Aluminium gallium indium phosphide (AlGaInP)
Aluminium gallium phosphide (AlGaP)
570 - 590 Yellow 2.1 - 2.2 Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium phosphide (GaP)
590 - 610 Orange / amber 2.0 - 2.1 Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaUInP)
Gallium phosphide (GaP)
610 - 760 Red 1.6 - 2.0 Aluminium gallium arsenide (AlGaAs)
Gallium arsenide phosphide (GaAsP)
Aluminium gallium indium phosphide (AlGaInP)
Gallium phosphide (GaP)
> 760 Infrared < 1.9 Gallium arsenide (GaAs)
Aluminium gallium arsenide (AlGaAs)

By Ian Poole


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