An emitter is any device used to emit any signal, beacon, light, odor, liquid, fragrance, or the like.

Drip irrigation

An emitter is a device used in drip irrigation to transfer water from a pipe or tube to the area to be irrigated. Typical emitter flow rates are from 0.16 to 4.0 gallons per hour, or 0.6 to 15.1 litres per hour. In many emitters, flow will vary with pressure, while some emitters are pressure compensating. These emitters employ silicone diaphragms or other means to allow them to maintain a near-constant flow over a range of pressures, for example from 10 to 50 PSI, or about 70 to 350 kilopascals.

Electronics

An emitter is often an LED, like the infrared ones used in remote controls for televisions. An emitter can also be wired into the integrated receiver/decoder of a satellite TV unit, so that it can operate a VCR to record a TV show when selected from the program guide. The wired emitter is stuck with an adhesive to the front of the VCR, and mimics the signals of the remote, eliminating the need to set the VCR separately. The term emitter also has specialized meanings in transistor and vacuum tube technology.