Monday, August 6, 2012

Scotopic Vision

We were watching the History Channel the other day and one of my kids asked about why all the night shots were green. Kids ask the craziest things.

The long/thin photoreceptors in the eyes, the rods, are responsible for vision under low light conditions. They provide Scotopic vision - low light vision. The term comes from Greek skotos meaning darkness and -opia meaning a condition of sight.

As it turns out, the rods are most sensitive to wavelengths of light around 498 nm (green-blue). In the graph above, the green bell-shaped curve represents scotopic vision (the rods) and the black represents photopic vision (the cones). The area where the two intersect - where both rods and cones are active - represents mesopic vision.

So, understanding how our eyes work in low light, the creators of night vision technologies peg the displays between 450-550nm - green.

With this answer, my kids responded ... cool.

For more information on the spectral response of the human visual system under scotopic conditions, click here.

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