The thin-film effect is the product of a very thin layer of liquid that distorts reflected light waves. This distortion is due to the phase difference of the light waves between the outer and inner surfaces of the liquid. The thickness of the film determines the colour of the effect. Since red light waves are longest (about 700 nm), and blue light waves shortest (about 400 nm), the thinner layer of liquid will be to the blue end of the light spectrum; the thicker layer to the red end of the spectrum. Bubbles exhibit the thin - film effect very well. All bubbles have some thickness of water which makes up their dome shape, but sometimes the surface does not noticeably diffract light into different colours. This is because the layer is either too thick or too thin, rendering infrared or ultraviolet wavelengths in the diffraction. Upon creation of the bubble, the diffracted light is invisible because the layer is too thick (diffracting infrared). Over a short period of time, the layer of liquid evaporate and the diffracted wavelengths become visible. During the life of a bubble, the diffracted light colour will progress from infrared to visible to ultraviolet. In my photograph, the bubbles are at the right stage to diffract visible light.

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Daven Hughes
Fredericton High School, Fredericton, New Brunswick
2nd Prize ( High School/CEGEP Class Project )

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