Infrared:  
Infrared light is part of the longer wavelength portion of the electromagnetic spectrum beyond the red region of the visible light spectrum. An ordinary camera using film sensitive to infrared light produces an infrared photograph. Cameras with a tube or a solid-state detector sensitive to infrared light are used in infrared reflectography; the resulting image is an infrared reflectogram. Infrared light penetrates varnish and paint layers, often revealing underdrawing or compositional changes beneath the paint layer.