A light valve projector uses a bulb as the source of light. The valve technology changes the colour and intensity of the source to form the picture. Film or slide projectors are examples of light valve technology. The Digital Micro-Mirror Device (DMD) also known as the Digital Light Processor (DLP), the Image Light Amplifier (ILA), and LCD are all examples of electronic light valve technology. Obtaining black in a picture produced by a light valve projector requires the ability to shut the light off in particular areas of the picture. Shutting light off in a small area is actually rather difficult. Consequently, the real picture contrast ratio of a number of these projectors is rather poor.