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Hey Ray! Why Flames Don't Cast Shadows

PITTSBURGH (KDKA) -- Shadows are pretty much an everyday or every night occurrence. Since light travels in a straight line, when something gets in the way of that path, it creates an absence of light, or a shadow.

(Photo Credit: KDKA Weather Center)

Not everything in the way of light causes a shadow, though, like other light sources. We are going to do an experiment that uses fire, so make sure you do this with a responsible adult.

(Photo Credit: KDKA Weather Center)

When we light this candle, the light creates a shadow on the candle in front of it. Now, if we light the other candle, the flame really doesn't cause a shadow, since light doesn't block light. The flame does not cast a shadow when the light sources are similar, so what if we ramp up the light shining on the candle?

(Photo Credit: KDKA Weather Center)

Notice, you can kind of see where the flame is, so something is going on! The flame is composed of more than just light. The fuel source and oxygen are big components in what you are seeing, and so is the heat the flame generates. Since the flame is much hotter than the surrounding air, it bends the light near the flame, creating the that wiggly line. Also, soot from the wick combusting can be seen as well. The light from the flame though, has no shadow.

(Photo Credit: KDKA Weather Center)

A different way to show this is with two flashlights.


A dim flashlight and a very bright one.

(Photo Credit: KDKA Weather Center)

The dim flashlight illuminates our poster board. That dim light does not block the brighter light, though, so it cannot cast a shadow.

(Photo Credit: KDKA Weather Center)

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