 |
 |
| What do you find scary?
Snakes? Spiders? Monsters? Or are you just afraid of the dark?
|
 |
| In the dark, your imagination runs wild. Even the tiniest noise can sound really scary.....
|
 |
| Thousands of years ago when night came, the only source of light was the moon. But if clouds covered the moon, things could get very dark indeed.
|
 |
| So - how did we invent light?
Well, all of the answers that inventors have come up with over thousands of years have one thing in common. To create light you have to find a way of releasing energy.
|
 |
| Burning something is probably the simplest way of creating light.
It was probably discovered by accident - maybe a lightning bolt hit a tree and set it on fire.
|
 |
| Whatever happened, people learned how to build wood fires, and their lighting problems were solved. But wood fires burnt out quickly and produced lots of smoke.
|
 |
|
Fat burns much slower than wood and isn't as smoky.
One of the next inventions was to thread string through certain species of birds and fish, to make them into oil lamps!
|
 |
|
This was really unpleasant, so someone worked out how to extract the oils and collect them in a bowl.
|
 |
|
But the fat still smelled horrible!
|
 |
|
The next state-of-the-art light machine was the candle.
When it was invented, the candle was considered to be exciting new technology.
|
 |
|
That's because the flame melts the wax around the wick, and the wick sucks the liquid gets to the top. The liquid gets so hot that it becomes a gas, and it's that gas that burns.
|
 |
|
Candles burnt much longer than wood fires and oil lamps. The earliest ones were made of animal fat. Much less messy than oil lamps and, if food was scarce, they could be eaten!
Don't try eating a candle!
|
 |
|
All of these inventions gave us more light than the moon.
The next invention was gas lamps. The clever thing about these was something called a mantle.
|
 |
|
It's a cotton bag coated in chemicals that contain metal. So when you light the gas, the cotton burns away leaving a delicate, brightly growing grid.
|
 |
|
For a while it seemed that nothing could rival gas lamps - until we discovered electricity.
|
 |
|
Today, most people use electric lights. But they're not all the same.
This is a halogen light - inside is a tiny wire that glows when electricity heats it up.
|
 |
|
Surrounding the wire is a halogen gas that allows it to glow brighter and for longer than an ordinary lightbulb.
|
 |
|
This is a neon sign - it doesn't have a wire inside, it has a different gas. It's called neon, which glows when an electric charge passes through it.
|
 |
|
You don't just need electricity to create light.
This is a light stick - if you crack it and shake, the two chemicals mix together and release energy.
|
 |
|
So - in a studio demonstration, Michael and Kate made a giant light stick.
In this large tube is a clear liquid called hydrogen peroxide...
|
 |
|
...and in this flask is a coloured liquid called luminol.
|
 |
|
When mixed together, they produce light - impressive, eh?
|
|
|
|
|
|
