Difference Between LDR and Photodiode

Light sensors, also known as photosensors, are among the most often used detectors in electrical applications. They are being used to control the amount of light.

One of the 7 fundamental physical characteristics is light intensity. The intensity of light monitoring is used in a variety of consumer, commercial, including practical points of view.

LDR vs Photodiode

The main difference between a LDR and photodiode is that a bidirectional resistance is an LDR. On the other hand, a unidirectional resistance is a photodiode.

Also, in comparison to a Light Dependent Resistor that is analog, photodiode has a faster reaction time.

LDR vs Photodiode

An LDR often referred to as a photoresistor, photodetector, or photoconductor, is just a light-dependent device.

It’s a form of resistor wherein resistance completely depends on how much light hits its body.

These resistors are commonly employed in many circuits that need the detection of light.

A photodiode is just a p–n junction semiconductors system that converts light energy into electrical energy. When radiation is absorbed inside the photodiode, electricity is created.

As the total area of a photodiode rises, the system response slows. A wide area photodiode is the most popular type of solar cell being used to create electrical solar power. 

Comparison Table Between LDR and Photodiode

Parameters of ComparisonLDRPhotodiode
BiasingIt is mostly employed in forward biasing.Unlike the LDR, which is used to detect fluctuating light levels, the photodiode is mostly employed in reverse bias, shutting off when a particular illuminance is reached.
Application and UsesThe most widely incorporated photo sensor is a Light Dependent Resistor.Whereas, Photodiodes are utilized in various applications that only have 2 alternatives: on or off.
Directionality of ResistorA Light Dependent Resistor is a bi-directional resistor.On the other hand, a photodiode is a unidirectional resistor.
Better Response TimeSince LDR is analog in nature, its response time is quite slow.Whereas, Photodiode’s response time is pretty good when compared to its peer.
Examples and InstancesStreet lamps are a demonstration of LDR still being used.Whereas, precision devices, such as laboratory gadgets, such as spectrometers, are representations of photodiodes in use.

What is LDR?

Throughout most processes that involve the need for a photosensor, the Light Dependent Resistor (LDR) is among the most extensively used and desired photoresistors.

Its most appealing feature is that it is both inexpensive and durable.

In addition, as the name implies, the light intensity beaming on them affects their susceptibility to electricity.

As a result, the amount of light they absorb has an inverse relationship with their resistance.

As a result, LDR photosensors are recommended when a variable quantity of illumination is expected rather than a constant intensity of light.

When a tough build is needed, the LDR is perhaps the sensor of choice.

This is particularly true whenever the sensor is used in a harsh and demanding environment. LDR has modest responsiveness and is also beneficial because it is a bidirectional resistance.

Both LDR (Light Dependent Resistor), as well as photodiodes are indeed the two primary categories of photosensors.

What is Photodiode?

The photodiode has a rapid response time by itself. Thus if your construction requires quick replies, this is the photodiode to choose.

The photodiode, like the LDR, is quite inexpensive. Unlike the LDR, which is then used to detect fluctuating light levels, the photodiode is mostly employed in reverse bias, shutting off because particular light intensity is surpassed.\

This indicates that now the photodiode offers two distinct current outputs. Whenever the light intensity is surpassed, it turns off; when the illuminance is adequate, it turns on.

In circumstances where it is necessary to keep track of light intensity, the photodiode is thus preferable.

Photodiodes are comparable to conventional semiconductor diodes, with the exception that they can be uncovered (to monitor vacuum UV or X-rays) or bundled with glass or optical fiber connections that allows light to penetrate the responsive component of the device.

To enhance the ability to respond, many diodes made specifically to be used as a photodiode use a PIN connection instead of a p–n junction.

Main Differences Between LDR and Photodiode

  1. Photosensors such as LDR as well as photodiode are broadly applied, with LDR being the most popular. It’s a light-dependent resistor that’s utilized in street lighting.
  2. It is also the photosensor of choice. The photodiode is applied in areas where there are just two options: on or off.
  3. In comparison to the LDR that is a light-dependent resistor, the photodiode has a faster reaction. It’s employed in a variety of undertakings. The photodiode is applied in accuracy gear, such as lab equipment spectrometers, and has a better response.
  4. When the light situation varies, the resistance of the LDR varies, and the voltage all across the photodiode shifts. Also, Silicon and Germanium are commonly used in photodiodes.
  5. A light-dependent resistor (LDR) is a resistor wherein resistance reduces as the intensity of light increases. Anode, as well as Cathode, are the two endpoints of a photodiode. This diode is typically employed in reverse bias, as well as the current flowing through it is determined by the amount of light that falls on its interface.
  6. Cadmium Sulphide is used to make LDR, which also has a resistance of up to 1 Mega ohm under dark settings. LDRs are low-cost and also have a wide spectrum of uses, including camera light meters, watches, blinky lights, and solar lamp posts, among others. When light strikes on a photodiode, it generates energy; ancient solar panels are nothing more than a huge photodiode. Optical disk players, smoke alarms, and television receivers are just a few examples.
Difference Between LDR and Photodiode


Photosensors are progressively being employed in numerous developments around the world nowadays, based on the basic premise of using lighting for detecting.

The line-following robots that will end up making use of such a unique technology are a perfect demonstration of photosensors in action.

Any venture that requires the use of photosensors must choose which kind of invention to deploy.

The Light Dependent Resistor (often termed LDR), as well as the photodiode, are indeed the two most prevalent types of photosensors.

The major determinant of where and when any sensor could be utilized is its distinct qualities.


  1. https://ieeexplore.ieee.org/abstract/document/9435280
  2. https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201502996
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