LDR and types of LDR

LDR and types of LDR
LDR and types of LDR

LDR and types of LDR LDR is a resistor that varies its electrical resistance value depending on the amount of light incident on it. It is also called photoresistor or photoresistance. The electrical resistance value of an LDR is low when there is light shining on it (in some cases, it can drop to as low as 50 Ohms) and very high when it is in darkness (it can be 1 Ohm or more).

LDRs are made from a photosensitive semiconductor crystal, such as cadmium sulfide (CdS). These cells are sensitive to a wide range of light frequencies, from infrared light to visible light, and even ultraviolet. Photoresistors made with cadmium sulfide are extremely sensitive to the range of light radiation that is visible in the human spectrum. Photoresistors made with lead sulfide are especially sensitive to infrared radiation.

It should be taken into account that the maximum dissipation is in the order of 50 mW-1W, and the maximum voltage that can be applied is 600V. The variation of the resistive value of an LDR has a certain delay, a typical response time in the order of a tenth of a second. The delay is different if you go from dark to light or from light to dark.

Introduction to Light Dependent Resistors (LDR)

Light dependent resistors, commonly known as LDRs (light-dependent resistors), are electronic components that have the peculiarity of changing their electrical resistance depending on the amount of light that falls on them. These devices are highly sensitive to light and are essential in a variety of applications.

Main Characteristics of LDR

  • Operation: LDRs are composed of semiconductor materials that alter their resistance when light falls on them. The higher the light intensity, the lower the resistance.
  • Applications: They are commonly used in alarm systems, lighting controls, light measurement devices, among others.

Sensitivity: They can be designed to be sensitive to different ranges of wavelengths, including infrared, visible light or ultraviolet.

How does an LDR work?

The LDR is a special type of resistor whose resistance varies depending on the intensity of light it receives. It is composed of a semiconductor material with a high resistance value that decreases as it is exposed to light. The principle behind this phenomenon is photoconductivity, which refers to the alteration in the conduction properties of a material when exposed to light.
In dark or low light conditions, the LDR has a high resistance, on the order of megaohms (MΩ), while under strong direct sunlight, the resistance can drop to a few hundred ohms.

Types of LDR

There are two main types of LDR:

    1. Intrinsic: These do not contain impurities and work on the principle of excitation of electrons from the valence band to the conduction band. However, they require high light energy to operate, which limits their practical use.
    2. Extrinsic: These contain impurities, which provide more free electrons and, therefore, greater sensitivity to light. They are the most commonly used due to their greater effectiveness and ability to operate in a wider range of lighting conditions.

The use of LDRs in modern technology continues to be a constantly evolving area, with improvements in efficiency and sensitivity. Below, we will explore in more detail how LDRs work, their structure, and some of the most interesting and advanced applications in which they are used.

Functioning and Structure of the LDR

LDRs work thanks to the ability of semiconductors to change their electrical properties in the presence of light. When light falls on the semiconductor material, the electrons gain energy and move, which reduces the total resistance of the component.

Innovative Applications

  • Automatic Lighting Control: LDRs are used in lighting systems to automatically adjust light intensity according to environmental conditions.
  • Motion Detection: In combination with other components, LDRs can be part of security and motion detection systems.
  • Photographic Industry: In cameras and photographic equipment, LDRs help automatically adjust exposure based on available light.

Applications of LDR

LDRs are used in a wide range of devices and systems, especially those that need to react in some way to light conditions. Some of these applications include:

  • Light sensors: Devices that need to respond to light conditions, such as automatic lighting systems, often use LDRs.
  • Security Systems: LDRs can be used in alarm systems to detect if a light has been turned on or off, or if a beam of light has been interrupted.
  • Consumer electronics: Many electronic devices, such as televisions, radios, and mobile phones, use LDRs to automatically adjust screen brightness based on ambient light conditions.
  • Photography: LDRs are used in cameras to help determine the correct amount of light for a proper exposure.

Considerations when using LDRs

When using LDRs, there are some important considerations to keep in mind:

  • Response Time: The LDR does not respond instantly to changes in light conditions. Therefore, it is not suitable for applications that require a rapid response to light fluctuations.
  • Spectral sensitivity: LDRs have different levels of sensitivity to different wavelengths of light. Therefore, they must be carefully selected based on the light source to which they will respond.
  • Temperature: The resistance of the LDR can also change with temperature, which can affect its operation in extreme environments.

Pros and cons

LDRs offer several advantages such as simplicity, low cost, and light sensitivity. However, they also have disadvantages such as their slow response in some cases and variability in their performance due to environmental factors.


Light-dependent resistors, or LDRs, are critical components in a wide range of technological devices and applications. With their unique ability to respond to light and alter its electrical resistance, LDRs have enabled advances in areas such as lighting, security and photography. Despite some limitations, their flexibility and low cost make them an attractive option for engineers and designers. Continued research and development in this field promises even more innovations and applications in the future, solidifying its place in modern technology

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