A New Color...

I've posted before about the strange phenomenon of visible ultraviolet light.  This was discovered in WWII when cataract patients serving off the coast of Nazi-occupied Europe reported that they could see the glow of German night troops using ultraviolet lights.  The German troops were equipped with an early form of night vision equipment that the Allies couldn't duplicate until near the end of the war.  But with the fortuitous discovery that cataract patients could see the lights, the Allies were able to detect when the German night troops were using this gear.

The cataract surgery back then involved complete removal of the eye's inner crystalline lens.  To compensate, the patients had to wear “Coke bottle” lenses in their glasses.  The natural crystalinne lense is opaque to ultraviolet light, but the external glass lenses were not – so for the first time in their lives, these patients had ultraviolet light impinging on their retinas.

Now a much more modern form of cataract surgery, in which the natural crystalline lens is replaced, has produced the same effect – because the replacement lens is made of material that is transparent to ultraviolet light.