Pepper's Ghost

Confuse your friends with ghostly candles, and find out how it is related to Victorian theater and fighter aircraft

What you need

What to Do

What may Happen

You should find that it looks like both candles are alight, until you look around the side of the glass.

What is going on?

Although glass is mostly transparent, it reflects a significant proportion of the light that hits it. Normally the light going straight through is so much brighter that you can't see it, but if you use something bright like a candle in front of the glass and a dim room behind, the reflection can dominate what you are seeing.

So you see the reflection really well. The neat thing about reflections is that they look as if the object is behind the mirror. So when you move your head, the reflection moves in exactly the same way as the candle behind, so the illusion works from lots of directions.

You don't have to just use a candle, a bright screen like the one on a mobile phone works too.

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This is how aircraft heads up displays work, which mean the pilot has useful information superimposed on his view of the world and he doesn't have to look away when he wants to know his altitude.

What has it got to do with theatre?

You don't have to use a screen, you could use an illuminated actor, then you would get a ghostly apparition reflected in the glass, which was semi-transparent and could interact with the other actors. This was a favorite of Victorian theatres and was called Pepper's Ghost.

Written by Dave Ansell