The Solar Spectrum Shows its Power

August 11, 2023

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Photographer: Dale Hugo

Summary Author: Dale Hugo 

This Afghan on our spare bed looks as though it has two black stripes on either side of a blue stripe. But the yarn colors are identical. The cell phone camera I used actually picks up a much more intense and lighter blue than does my eye, which tells me it’s navy while through the camera lens it seems medium blue. What’s going on here? Direct sunshine came through our horizontal blinds (from left side of the photo) the morning I noticed this oddity. Room light was provided only by scattered sunlight, not incandescent light or LED’s. But the sunlight has a strong blue component that happened to strike the broad, blue band and not the narrow ‘black’ bands. I had to stop and look carefully after I asked myself, “Where did this blue color come from? I’ve never seen blue on this old Afghan before!” The section shown here is about 7 inches (18 cm) long, top to bottom.

Blue has more energy than the longer wavelengths. I suspect that it penetrates deeper into the fibers and is scattered less than the other colors. Remember Roy G. Biv, from middle school science classes? It’s the spectral sequence; red, orange, yellow, green, blue, indigo and violet — the last three have the highest energy and the shortest wavelength.


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