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Color and Light · entry 45 of 52
Soap bubbles show shifting colors because thin films interfere with reflected light waves.
The longer version
Light reflecting from the outer surface of a soap film meets light reflecting from the inner surface. The two waves have travelled slightly different distances, so they interfere, reinforcing some wavelengths and cancelling others depending on how thick the film happens to be at that spot.
Because the film thins and drains under gravity, the reinforced wavelength changes from moment to moment and the colours swirl. Where the film becomes extremely thin, all visible wavelengths cancel and the spot turns black just before bursting. Thickness determines hue, so the same physics colours cracks in ice and the sheen on some beetles.
Where this entry sits
These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.
More From Color and Light
Eight more entriesOil on wet pavement shows a rainbow pattern for the same reason thin soap films do.
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Read 49Blue pigments are rare in nature, so most blue animals rely on structure instead.
Read 50Cameras capture color by filtering light through red, green, and blue sensors.
Read 51Printed images use cyan, magenta, yellow, and black ink to reproduce many colors.
Read 52Stop signals are usually red because the color stands out against most natural backgrounds.
Read 1The human eye detects color using three types of cone cells sensitive to red, green, and blue light.
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