The green effect present in most night vision devices is due to a phosphor screen. The phosphor screen acts as a device to help enhance the image, allowing you to see details with the goggles.

http://cdn.explainthatstuff.com/how-night-vision-works.jpg

I don't know why the devs never put night vision into FO3, because there already was a perk of this kind in FO1/2 who never was of real use at that time. But considering the night vision mods in FO3 it could be quite possible in New Vegas to use the night vision effect.

The best use would be the night vision integration with the power armor helmets as these powered suits already come with plenty energy support for the helmets and night vision needs energy.

Night vision should be able to toggle automatically based on light level or there should be a script command that can detect light level. Because I'm not sure I always want to switch night vision manually all the time.

in FO3 i never noticed a place where night vision goggles were needed and im sure in FO:NV it will be the same but i would like in later versions if there was much darker places to wander around that either a perk that let you see clearer in the dark and/or night vision goggles or scope or even flash light helped you out in these areas.

The first night vision devices were introduced by the German army as early as 1939. . The "Vampir" man-portable system for infantrymen was being used with Sturmgewehr 44 assault rifles.[4] Parallel development of night vision systems occurred in the USA. The M1 and M3 infrared night sighting devices, also known as the "sniperscope" or "snooperscope", were introduced by the US Army in World War II, and also used in the Korean War, to assist snipers.[2] They were active devices, using a large infrared light source to illuminate targets. Their image intensifier tubes function using an anode and an S-1 photocathode, made primarily of silver, caesium, and oxygen to accelerate the electrons.[5]

Bloody'ell. Beat to the punch.
Point remains though. Viable technology for the game setting and after looking at the early version (Vampir) appropriate 'feel'.
(and mods don't help console users ~sniff~)