Friday, 19 December 2014

Strange flashing light

Pepper's ghost reflectionThere was no sound just a strange flashing in my peripheral vision. I looked down to where the light was coming from but could see no obvious cause. Then I noticed a clear plastic bag on the floor that had not been there before. Experiments showed that, as it fell, it reflected light from a nearby bulb as a series of flashes. Is there no end to weird stuff caused by normal stuff?

Clear plastic bags are particularly good at producing strange effects. They blend in well with their background and so are often not noticed. But they can reflect strongly from a light source when at the correct angle. So, a clear plastic bag on the floor of a dimly lit room might be invisible until an observer moves. Then it might reflect a light source strongly, but briefly, while the witness is moving. The result is an unexplained light or flash. Even if the scene is examined closely at the time, the plastic bag may not seem to be an obvious source of an unexplained light.

When clear plastic bags are new they have very flat surfaces. But they soon acquire wrinkles after use. These wrinkles can produce multiple highlights which might together form a shape, maybe even suggesting a glowing face. Coloured plastic bags aren't so prone to producing odd light effects. They tend to be less shiny and don't blend in to their background like the clear ones.

The photo shows a printed plastic slide in front of tiles. It is strongly reflecting a nearby light source. See here for more on reflections.

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