Asked by: David Connolly

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Colour-changing light bulbs use red, green and blue LEDs to create their range of colours, switching them on in different combinations using a tiny computer (‘microcontroller’). Red, green and blue LEDs are used because our eyes have colour-sensitive cells called cones that are roughly attuned to these three wavelengths of light, and we see colours as different combinations of these wavelengths.

If you want yellow, the bulb turns on red and green. For cyan, it turns on green and blue. For white, it turns them all on. To fine-tune the shades of colour, the bulb also pulses the LEDs very quickly – if it pulses blue so that it’s on only 50 per cent of the time, for example, we see a darker blue. With these tricks, colour-changing bulbs can create millions of subtly different colours.

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Authors

Dr Peter Bentley is a computer scientist and author who is based at University College London. He is the author of books including 10 Short Lessons in Artificial Intelligence and Robotics and Digital Biology: How nature is transforming our technology and our lives.

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