Editing User Adaptor (section)

== Simple light sensor ==

[[File:Circuit-User-Light-Sensor.svg|frame|left|Fig. 1]]

The circuit shown in fig.1 uses a light dependent resistor (L.D.R.) to form a light sensor.
The L.D.R. and the 220Ω resistor form a potential divider.
The resistance of the L.D.R. increases as the light falling on it decreases.
In very dark conditions the resistance will be at least 1MΩ so only a small voltage will be present at the input socket.
In bright conditions the L.D.R. will have a resistance similar to the 220Ω fixed resistor and so the input socket will see a voltage of around 2.5 volts which will give a maximum sensor reading of 255. Typical uses of this type of sensor include:

* Measuring daylight during the day to determine if it has been ‘sunny’ or ‘overcast’
* Detecting dusk and switching on a security lighting system.
* Measuring the amount of light which passes through a variety of materials.

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