Twilight switch

from Wikipedia, the free encyclopedia
A very simple twilight switch. If the ambient brightness drops, the current flows from the variable resistor instead of through the photo resistor (LDR) through the transistor Q, and thus switches the lamp on.
American electromechanical twilight switch. Construction of a light-dependent resistor , in the dark the heating coil of the thermal bimetallic switch cools down and switches on the circuit.

As a light-sensitive switch is known an electrical device if an adjustable brightness value is exceeded or fallen short, which has the function to activate a switch contact.

Most of the twilight switches available on the market switch at the onset of darkness when the brightness value is undershot, e.g. B. their load (z. B. a lamp) on at dusk and off again at the onset of brightness, when the brightness threshold is exceeded again, i.e. around dawn. Less common are those in which, conversely, it is switched on when it is bright and switched off when it is dark. For modern PV systems , where self-consumption is in the foreground, such "inverted" twilight switches or "brightness switches" are useful, since electrical devices can be switched on automatically at dawn when the PV system is producing electricity.

Model types

  • Twilight switch with integrated sensor
  • Twilight switch with external sensor

function

In older twilight switches, a so-called is photoresistor ( English Light Dependent Resistor , LDR), a light-dependent resistor, the light intensity dependent change of the electric resistance is used for the switching command. Today electronic components (phototransistor, photodiodes) are often preferred to the LDR.

Web links

Commons : Twilight Switch  - Collection of pictures, videos and audio files

Specialist literature

  • Helmut Röder, Heinz Ruckriegel, Heinz Häberle: Electronics 1st part, basics of electronics. 8th edition, Verlag Europa-Lehrmittel, Wuppertal, 1980, ISBN 3-8085-3178-9
  • Wilhelm Gerster: Modern lighting systems for inside and outside. 1st edition, Compact Verlag, Munich, 1997, ISBN 3-8174-2395-0