Infrared is used in <answer>night vision</answer> equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of ambient light photons into electrons that are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to augment the available ambient light for conversion by <answer>night vision</answer> devices, increasing in-the-dark visibility without actually using a visible light source.
What sort of equipment uses the infrared spectrum in the absence of sufficient visible light?
night vision