Science Questions

Why do night vision goggles traditionally produce a green image?

Chris -   I think this is probably a legacy of our pre-LCD era.  We take for granted having these flat screen, very light screens now, but in the old days, not so long ago actually, we relied on cathode ray tubes, these big old giant television-like things that we had in our living rooms and that technology could be condensed down to something fairly compact but still quite bulky which was the way of making an image on a screen.  Green is a good choice for two reasons.  One is that the phosphors, the things that glow and make the colour are relatively easy to make it green.  And because the eye is more sensitive to green light than virtually any other wavelength, it means that you can make your display dimmer than any other wavelength and your eye will be sensitive to it.  And it means therefore, you can run your thing with less power than you would otherwise need to make another colour visible so green’s a good choice.  And I think also when you’re looking with night vision goggles, you’re actually seeing monochrome anyway, it’s a black and white picture anyway.  There’s no colour information that can be conveyed so it doesn’t matter that it’s only just in one colour.

Ron -   And the dragon fish that live in the deep sea that are as mentioned just now that see red light.  They actually see the red light using chlorophyll and the laboratory in the states have now started putting chlorophyll into the eyes of mammals, things like rats and mice and have been able to make them super sensitive to red and there’s even been the suggestion that you could do this with humans so that you can make them almost infrared sensitive and you wouldn’t need goggles at all.

Chris -   So this would be a sort of military application.  You could give your pilots or your armed personnel super red vision so that they could see the enemy on the battlefield glowing because they’re putting out heat.

Ron -   Absolutely, theoretically as you would say.

Chris -   That’s wonderful.  Thank you Ron.

July 2009