Tuesday 22 January 2019

Where do the blue stripes go? The wonderfully simple science behind this optical illusion

It’s the same reason you don’t get sunburn through a car window.


By Nilima Marshall and Edd Dracott, Press Association

A physicist has explained an optical illusion which has been bugging users on Reddit.

The image was posted by user soupface2, a 33-year-old nursing student from New York, and shows her glove that in one image appears to be one colour and the other to have blue stripes.

The gloves

“What’s occurring here is a process of light filtration – the yellow window in the first picture filters out certain wavelengths of light including the specific shade of blue normally seen in the stripes of the gloves,” she told the Press Association.

“In the second photo I’ve opened the door, letting in normal light from the sun with no filter, so now blue light can hit the glove’s surface and reflect off the stripes, making them appear blue.”

The image has received over 72,000 upvotes on Reddit, and Brad Gibson, head of physics at the University of Hull agrees with her diagnosis of the phenomenon.

“All glass does this to some degree, for example, most glass filters out ultraviolet light, which is why you don’t get a sunburn with the car window closed,” he said. “The glass is filtering short wavelength light.

“The glass in this image is doing the same, but instead of just blocking ultraviolet light, it is also blocking somewhat longer wavelength light (into the blue part of the spectrum) but letting longer wavelength light through (the yellow and longer part of the spectrum).”

Press Association

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