IR can be used during any time of day. Versions of IR can be White Hot (black background while the "heat signature" is white), Black Hot (reverse if White Hot), or Full Spectrum Color (not as good for use during the day). What is commonly known as "night vision" is just the camera amplifying ambient light. It can be either what was once called "red haze" or "green haze" back in the 70's. All of those technologies were R&D'd during Vietnam.
IR can be used during any time of day. Versions of IR can be White Hot (black background while the "heat signature" is white), Black Hot (reverse if White Hot), or Full Spectrum Color (not as good for use during the day). What is commonly known as "night vision" is just the camera amplifying ambient light. It can be either what was once called "red haze" or "green haze" back in the 70's. All of those technologies were R&D'd during Vietnam.