This simple circuit

This simple circuit has a rgb LED capable of lighting up red, green and blue. Each of those colours is controlled by those controls (variable restores called potentiometers) at the bottom. So by turning on just one we can have red, green or blue light. By turning on blue and green we can have the secondary colour of cyan. By turning on blue and red we get magenta and with just green and red we have yellow. All three on? White light of course.

So what’s the relevance of this?

Year 7: they’ve learnt how to build simple circuits, drawing circuit diagrams with the correct symbols and learning about components and how to use them.

Year 8 and 9: this is a brilliant way to show the primary and secondary colours of light. There are people out there who think the primary colours are red, blue and yellow! Not so. All the colours we see in transmitted light are made from red, green and blue. That’s how your eye, your computer or phone screen works. If you’re mixing paint or inks you need the secondary colours of transmitted light to be your primary colours of reflected light: magenta, cyan and yellow (that’s why those are the cartridges in your printer).

A Level: This circuit is a potential divider. We can calculate the current through and voltage across the LEDs. An LED is a low power semiconductor diode, invented in 1967 and now ubiquitous. We can explain how it emits light by being a quantum device.

This simple circuit
A Level Physics student, Manfred, made a more elegant version of the colour LED mixer

We can also control this circuit with a computer such as the Raspberry pi. But that a story for another day.

Mr Ayd Instone, Head of Physics