Light Dependent Resistors (LDR) are also know as Photoresistors. LDR are popularly used in our modern day automation applications. Lights Dependent Resistors are electronic components are sensitive to light. Light is made of photons hence the name photoresistor is part of it too. LDR’s have wide range of applications including light sensing, light measurement or luminosity, and can control electronic devices just with change in resistance.
- 1 x 100 Ohm Resistor
- 2 x LED
- 1 x Photoresistor
- Jumper Cables
Light Dependent Resistor
The working principle of LDRs is based on the photoconductive effect, which simply can be referred to as the surface of the LDR becomes more conductive in the presence of visible light. When light falls on the surface of an LDR, the energy from the light is absorbed by the semiconductor material, which results in the creation of electron-hole pairs. These electron-hole(positive charge) pairs increase the conductivity of the semiconductor material and decrease the resistance of the LDR.
How does a LDR work in the Circuit?
The LDR in the presence of light offers less resistance to current and in the absence if light it gets highly resistive. Now consider an example, that there are two roads to head one with all obstacle and the other with no obstacles at all. In this case we are more likely to take the road with no obstacles. In the circuit below the Resistance offered by the LDR will decide how much of the current will flow through the LDR .
Circuit Diagram for Brightness Controller
The LDR in this circuit just acts as a resistor. With this circuit you will be able to observe that the brightness of the LED will increase as you flash some more light on LDR. If you connect this circuit in a very dark place, please note that you might not be able to see it working.
The Brightness of the LED increases as the resistance of the LDR decrease with more light on it. The same photoresistor will be used to explain the understanding the transistor. That circuit called as the dark detector will light up in the dark and turn off during the light. The LDR is of great application as it is used in alarm clocks, automatic street lights, and day and night detection circuits.