Involves a small lamp adjusted to direct a narrow light beam across the detection chamber Next to this light source, but hidden from direct exposure to the beam, is a light-sensitive photocell Smoke entering the detection chamber scatters the light beam reflecting it in all directions Some of this reflected light is picked up by the photocell which, at a preset level, triggers the alarm
Ejection of electrons from a substance by incident electromagnetic radiation, especially by visible light. Phenomenon in which charged particles are released from a material when it absorbs radiant energy (see radiation). It is often thought of as the ejection of electrons from the surface of a metal plate when visible light falls on it. It can also occur if the radiation is in the wavelength range of ultraviolet radiation, X rays, or gamma rays. The emitting surface may be a solid, liquid, or gas, and the emitted particles may be electrons or ions. The effect was discovered in 1887 by Heinrich Hertz and explained by Albert Einstein in work for which he received the Nobel Prize