which type of fire detector uses the effect of smoke on a light source and photo-electric cell
optical smoke detector
title: Smoke detector text: Smoke detector A smoke detector is a device that senses smoke, typically as an indicator of fire. Commercial security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household smoke detectors, also known as smoke alarms, generally issue a local audible or visual alarm from the detector itself. Smoke detectors are housed in plastic enclosures, typically shaped like a disk about in diameter and thick, but shape and size vary. Smoke can be detected either optically (photoelectric) or by physical process (ionization); detectors may use either, or both, methods. Sensitive alarms title: Smoke detector text: where air, which may contain smoke from a nearby fire, flows. In large open areas such as atria and auditoriums, optical beam or projected-beam smoke detectors are used instead of a chamber within the unit: a wall-mounted unit emits a beam of infrared or ultraviolet light which is either received and processed by a separate device, or reflected back to the receiver by a reflector. In some types, particularly optical beam types, the light emitted by the light source passes through the air being tested and reaches the photosensor. The received light intensity will be reduced due to scattering from title: Smoke detector text: radiation. Some European countries, including France, and some US states and municipalities have banned the use of domestic ionic smoke alarms because of concerns that they are not reliable enough as compared to other technologies. Where an ionizing smoke detector has been the only detector, fires in the early stages have not always been effectively detected. A photoelectric, or optical smoke detector contains a source of infrared, visible, or ultraviolet light (typically an incandescent light bulb or light-emitting diode), a lens, and a photoelectric receiver (typically a photodiode). In spot-type detectors all of these components are arranged inside a chamber title: Smoke detector text: the need for external wiring. Ionization smoke detectors are usually cheaper to manufacture than optical detectors. They may be more prone to false alarms triggered by non-hazardous events than photoelectric detectors, and have been found to be much slower to respond to typical house fires. Americium-241 is an alpha emitter with a half-life of 432.6 years. Alpha particle radiation, as opposed to beta (electron) and gamma (electromagnetic) radiation, is used for two additional reasons: alpha particles have high ionization, so sufficient air particles will be ionized for the current to exist, and they have low penetrative power, meaning they will title: Smoke detector text: encasing the detector. The 10-year-lithium-battery-powered smoke alarm was introduced in 1995. The photoelectric (optical) smoke detector was invented by Donald Steele and Robert Emmark of Electro Signal Lab and patented in 1972. An ionization smoke detector uses a radioisotope, typically americium-241, to ionize air; a difference due to smoke is detected and an alarm is generated. Ionization detectors are more sensitive to the flaming stage of fires than optical detectors, while optical detectors are more sensitive to fires in the early smouldering stage. The smoke detector has two ionization chambers, one open to the air, and a reference chamber which