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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