The structure of LCDs is a combination of liquid crystals sandwiched between two clear panels and polarizing filters that allows light to pass through in only one direction. The light source is a lamp positioned behind the display. Fluorescent lamps are commonly used in direct-view displays. Most calculators and watches use reflective panels that can be viewed when enough surrounding light is available. The polarizing filter can pass only the light component from the light source that is parallel to the direction of its axis, and the molecular arrangement of liquid crystals determines whether that light passes through them or is blocked. This structure can represent white/black by turning power on/off. Adding red, green, and blue filters enables display in color.