If you’re not familiar with the terms “LDR” and “photodiode,” you’re not alone. Many people are confused about the difference between these two components, even though they both have to do with light. In this blog post, we’ll clear up any confusion and explain the key differences between LDRs and photodiodes. By understanding the differences, you’ll be able to select the right component for your project. Stay tuned!
What is LDR?
An LDR or light-dependent resistor is a type of variable resistor whose resistance decreases with increasing incident light intensity. In other words, it is a sensor whose resistance changes when exposed to light.
- The resistance of an LDR can be as high as several megaohms (MΩ) in the dark, while exposed to bright light its resistance can drop to a few kilohms. The figuring and construction of LDRs depend on the semiconductor material used. The first LED was made from silicon, germanium, and selenium alloys. A more recent development is the cadmium sulfide (CdS) cell.
- With modern production techniques, it has become possible to manufacture recombination centers very precisely in the CdS crystal so that their size can be smaller than the wavelength of visible light. As a result, the electrical conduction mechanism in CdS cells is now diffraction limited and extremely sensitive to changes in incident light intensity.
- Newer materials such as indium gallium arsenide (InGaAs) are also being investigated for use in LDRs. LDRs are used extensively in light-sensitive applications such as optical switches, photodetectors, and infrared (IR) sensors.
They can also be used to automatically control the brightness of streetlights, car headlights, and indoor lighting depending on the ambient light conditions. One common use for an LDR is in everyday digital cameras where they are used to control the camera’s iris aperture. By varying the aperture size, more or less light can reach the image sensor, resulting in brighter or darker images. LDRs are also commonly used as burglar alarm sensors and in automatic room lighting controls.
What is Photodiode?
A photodiode is a silicon semiconductor device that converts light into an electrical current. Unlike a regular diode, a photodiode is designed to operate in reverse bias, meaning that the Photodiode voltage is always opposed to the Photodiode current. When light hits the Photodiode, it generates minority carriers that are swept away by the electric field, creating a Photodiode current. The amount of current generated by the Photodiode depends on the intensity of the light and the area of the Photodiode exposed to light. Photodiodes are used in a variety of applications, including optical communications, motion detection, and solar energy conversion.
Difference between LDR and Photodiode
LDR is a Light Dependent Resistor whose resistance decreases with the intensity of the incident light. In contrast, a photodiode is a semiconductor device whose electrical resistance decreases when exposed to light. Both LDR and photodiode are used for sensing information about the intensity of light.
- LDRs are made of semiconductor materials such as cadmium sulfide (CdS), which have an intrinsic property of high resistance to the flow of electric current. When there is no incident light on the LDR, its resistance is very high.
- This is because the CdS molecules are not excited by the incident light and, as a result, they do not allow electrons to flow freely through them. However, when incident light falls on the LDR, its resistance decreases. This is because the photons in the incident light cause the CdS molecules to become excited and allow electrons to flow more freely through them.
- Photodiodes also have semiconductor materials such as silicon (Si), but they work on a different principle. In a photodiode, when there is no incident light, the junction between the p-type and n-type semiconductor materials is reverse-biased.
This means that there is a potential difference across the junction that prevents current from flowing through it. However, when incident light falls on the photodiode, it causes electrons in the p-type material to be excited and flow across the junction into the n-type material. As a result, current flows through the circuit, and the voltage across the junction drops.
This current can be measured and used to calculate how much light is shining on the sensor. A photodiode also has two terminals, but instead of a resistor, it has a capacitor. When light shines on the photodiode, it creates an electric current that charges up the capacitor. The amount of charge that builds up can be measured and used to calculate how much light is shining on the photodiode.