As kharmael says
NVGs amplify what they see - generally speaking the 'light' they amplify is within the ' Near Infra Red' spectrum- above 600nm - therefore just outwith the visible spectrum (dependant upon the NVG and the 'minus blue' filter attached to the NVG- if the operator is new to this technology don't assume that the NVGs have a minus blue filter fitted as standard- I have been caught out by this in Poland!)