The Daily Item, Sunbury, PA

Technology

February 22, 2013

Slate: Another pair of eyes



By Phil Plait

Slate


Look around you. What do you see?

You may have an amazing array of objects around you that you can see in fine detail, their colors vivid and bright, what seems like an amazing variety of hues.

But think on this: What you’re seeing is just an incredibly small slice of what’s actually there. Our eyes are sensitive to only a relatively few colors available in the electromagnetic spectrum — the scientific term for “light”. The bluest color we can see has a wavelength of about 400 nanometers (a nanometer is a billionth of a meter; for comparison, a human hair is 100,000 nm wide), and the reddest about 700 — not even a factor of two in range! But light can have wavelengths far smaller than a nanometer at one end of the spectrum, and kilometers long at the other (theoretically, there is no limit to how long a wavelength can be).

Near-infrared (NIR) light has a wavelength just outside what we can see on the red end, with wavelengths from 800 to roughly 2000 nm (NIR is more of a generic term than a specific color range). While our eyes can’t detect it, the light-sensitive chips in cameras usually can. And when you use a filter that blocks visible light but lets through the NIR, the world looks different. Mostly the same, but with an odd twist, a skewed balance of brightness that makes it seem unearthly, delicate and beautiful.

Photographer Andrew Hurtleff took advantage of this to create an astonishing time-lapse video using infrared images, which he calls Movements in Red.

The shots making up the video are familiar scenes, but the lighting is just peculiar. The most obvious change is that leaves appear bright white, almost glowing. Leaves absorb almost all wavelengths of visible light except for green, which they reflect. When that light hits our eyes, we see the leaves as being green (ironically, we say the leaves are green, when in fact that’s the color of light they reject).

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