What is the working principle of LDRs?
The working principle of an LDR is photoconductivity, which is nothing but an optical phenomenon. When the light is absorbed by the material then the conductivity of the material enhances. When the light falls on the LDR, then the electrons in the valence band of the material are eager to the conduction band.
Where can LDRs be used in real life applications?
Applications:
- The LDR is used in the infrared astronomy.
- The LDR is used in light failure alarm circuits and used in light meter.
- The LDR used in smoke detectors.
- It is used for automatic contrast and brightness control in television receivers.
- It is used in photosensitive relay.
- It is used in optical coding.
How does a Light Dependent Resistor work LDR?
When the light level decreases, the resistance of the LDR increases. As this resistance increases in relation to the other Resistor, which has a fixed resistance, it causes the voltage dropped across the LDR to also increase.
Why are LDRs used in street lights?
LDR sensor is used for detecting the presence of surrounding light so that during the day time when sun is bright, the street light is switched off automatically. During the night time when there is no light, the LDR sends signal to microcontroller to turn on the street light.
Are there two types of LDR?
– Ultraviolet LDR: more active to ultraviolet light, including cadmium sulfide, cadmium selenide LDR, etc., used for UV exploration. – Infrared LDR: Lead sulfide, lead telluride and lead selenide are the main ones.
How are LDRs used in mobile phones?
The full potential of the LDR is made use by connecting them in a voltage divider circuit. In the second image, the resistance R2 is replaced with the LDR and using the given formula the voltage accross the LDR is measured. As the resistance of the LDR changes, the voltage across it changes as well.
How is LDR measured?
Keep the multimeter at Ohms mode. The LDR must be subjected to a bright light source (day light is enough). Connect the LDR leads to the multimeter terminals as shown in the figure. Now the multimeter will show a low resistance reading around 500 Ohms.
What is the resistance of LDR?
Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but when they are illuminated with light resistance drops dramatically.
Which effect is used in LDR?
The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases. A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.
What are the types of LDR?
According to the spectral characteristics of LDRs, there are three types of LDRs: – Ultraviolet LDR: more active to ultraviolet light, including cadmium sulfide, cadmium selenide LDR, etc., used for UV exploration. – Infrared LDR: Lead sulfide, lead telluride and lead selenide are the main ones.