Sep 012014
 

LDR – Light Dependent Resistor – Photoresistor

The LDR (light dependent resistor) is a resistor that has a value that varies depending on the amount of light it has on it. The photoresistor (LDR) symbol is:

LDR (Photoresistor) Symbol

The LDR is manufactured with crystalline structure materials using its photoconductive properties. The most common crystal used are: cadmium sulphide and cadmium selenide.

LDR´s range values goes from 50 ohms to 1K (1000 ohms) when it is fully illuminated and from 50K (50000 ohms) to several MegaOhms when it is dark. Its value (Ohms) does not vary instantly when it moves from darkness to light or from light to darkness, and the time the LDR takes in this two processes is not always the same.

This is why the LDR can not be used in many applications, especially those that need a lot of accuracy in time (the time it takes to change its state from dark to light or from light to darkness) and the accuracy of the values of the LDR on the same previous statements. Its typical response time is approximately 0.1 seconds.

However there are many applications in which a photoresistor is very useful. There are cases where the accuracy of the changes is not important.

For example

  • Automatic activation night light which uses a photoresistor to activate one or more lights (lamps) when the night comes.
  • Light controlled Relay where the lighting state of the photoresistor, enables or disables a relay. This kind of circuit can have a large number of applications.

The LDR is an extremely useful element, especially when we need to detect the absence of light.

Please like & share:

Related Post

Voltage Regulator with current limiter Voltage Regulator with current limiter using transistor and Zener diode There are times when the amount of current that is required of a power supply...
The sinusoidal oscillator (basic structure) Basic structure of the sinusoidal oscillator The sinusoidal oscillator basic structure consists of an amplifier (A) and a selective frequency netwo...
Tolerance of a Resistor Resistor tolerance The tolerance of a resistor is data that tells us the percentage that can vary the resistance value of its proposed value. ...
Schottky Diode The Schottky Diode The Schottky diode symbol is showed on the diagram. The Schottky diodes unlike the semiconductor diode that has a P-N...
Semiconductor Diode Tutorial The Semiconductor Diode The semiconductor diode is the simplest semiconductor device and can be found in almost any electronic circuit. Diodes a...
How to use a multimeter to test resistors How to use a multimeter to test resistors Note: Due to the existence of a wide variety and types of multimeters we will explain the most ...
Electrical Resistance The Electrical Resistance The electrical resistance is a measurement of the opposition that offers a material to the passage of electrons (the ele...
Phototransistor equivalent circuit Phototransistor equivalent circuit A phototransistor is essentially the same thing as a common transistor, which can work in 2 different ways: ...
 Posted by at 3:36 pm

 Leave a Reply

(required)

(required)

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>