Any technique to enhance vision under low light conditions, either by intensifying the existing light or using parts of the electromagnetic spectrum outside the range of visible light. Image-intensification systems use photomultipliers to raise very low light levels up to a level more convenient for viewing. Devices tailored for the infrared spectrum, such as charge-coupled devices (CCDs), are also used to convert that part of the spectrum into visible monochrome images, a technique often referred to as thermal imaging. Night vision systems were originally developed for military, law-enforcement, and security use, but are increasingly found in more everyday aspects of life, such as vision enhancement screens on high-end cars.