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Rainbow torch

By David, 25 November 2021 Activity

9 volt batteries with LED's attached casting coloured lights.

When you mix additive colours together, you’ll get something brighter.

Ever wondered how TVs can make so many colours? Make some coloured torches and learn to blend like a TV in this activity from our book, Puzzles and Projects.

You will need

  • 3 nine-volt batteries
  • 3 360 ohm resistors*
  • 1 red LED
  • 1 blue LED
  • 1 green LED

These items can be found at an electronics store.

*Tip: When looking for 360 ohm resistors, the stripes will be either orange, blue, brown, and an additional colour; or orange, blue, black, black, and an additional colour.

What to do

  1. 9 volt battery, LED and 360 ohm resistorGrab one battery, one LED and one resistor.
  2. Work out which leg of the LED is shorter. If you can’t tell which is shorter, the LED will be smooth on the side of the short leg, and have a bump on the side with the long leg.
  3. resistor wire twisted around the short leg of the LEDTwist one end of the resistor around the short leg of the LED
  4. Bend the other end of the resistor into a U-shape.
  5. Other wire of resistor attached to battery terminal.Put the U shape around the big terminal on the battery. You might need to make the U bigger or smaller to make it grip the terminal.
  6. Other leg of LED is attached to the other battery terminal.Touch the long end of the LED to the small battery terminal. The LED will light up!
  7. Three batteries lined up with their conneced LEDsRepeat these steps with the remaining parts to make three LED torches in three different colours
  8. Three coloured torches shining together making a white lightIn a dark room, point the three torches towards a white surface. Experiment with colour mixing by turning on different combinations of colours. You can make them brighter and dimmer by moving them closer or further away.

 

What’s happening?

Coloured lights are known as additive colours. They add new light to a dark area. When you mix additive colours together, you’ll get something brighter.

The primary additive colours are red, green and blue, similar to the colours of the LEDs in this activity. If you get the ratios right with these LEDs, you can make something very close to white light!

Have you ever wondered how your computer screen, smartphone or TV makes so many different colours? Every colour on these screens is actually a combination of just three different lights – red, green and blue. There are millions of different combinations to choose from, so screens can look very realistic. But there are some colours, including intense blue-greens and the violets at the end of the rainbow, that screens still can’t reproduce correctly!

This activity comes from our latest book, Puzzles and Projects. This book features some of the best hands-on activities, puzzles, stories and more from Double Helix magazine. Plus, there’s stacks of new content to explore!

You can buy a copy for yourself or a loved one on the CSIRO Publishing website, or pick it up from your favourite bookstore.

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