LDR - Important Concepts

IDIOMA (LANGUAGE) : ESPAÑOL


WHAT IS A PHOTORESISTOR OR LDR?

The LDR for its acronym in English (Light Dependent Resistor) or photoresistor is a resistance which varies its value depending on the amount of light that hits the surface. The greater the intensity of light that hits the surface of the LDR or photoresistor, the lower its resistance and the lower the light that hits on it, the greater its resistance.

HOW DOES AN LDR OR PHOTORESISTANCE WORK?

When the LDR (photoresistor) is not exposed to light, the electrons are firmly united in the atoms that make it up, but when light radiates on it, this energy releases electrons with which the material becomes more conductive, and from this way decreases its resistance. The LDR resistors only reduce their resistance with a luminous radiation located within a certain band of wavelengths. The photoresistor built with cadmium sulfide are sensitive to all visible light radiations and those built with lead sulfide are only sensitive to infrared radiation.

FABRICATION MATERIAL

The most photosensitive materials for the manufacture of LDR resistors are thallium sulphide, cadmium sulphide, lead sulphide and cadmium sulphide.

OHMIC VALUE

When we measure between its extremes we will find that they can reach values in the dark near megaohm (1MΩ) and exposed to light we will measure values around 100Ω .

TECHNICAL CHARACTERISTICS OF THE LDR

LDR CHARACTERISTICS

  • Typical values vary between 1 MΩ or more in the dark and 100MΩ in bright light.

  • Maximum dissipation (50 mW – 1W)

  • Maximum voltage (600V)

  • Spectral response

  • The typical response time of an LDR is in the order of one tenth of a second.

LDR ADVANTAGES

  • High sensitivity (due to the large area it can cover)

  • Easy employment

  • Low cost

  • There is no union potential

  • High light-dark resistance ratio

LDR DESADVANTAGES

  • Narrow spectral response

  • Hysteresis effect

  • Low temperature stability for the fastest materials

  • The variation of the value of the resistance has a certain delay, different if it goes from dark to illuminated or from illuminated to dark. This limits the use of LDRs in applications where the light signal varies rapidly.

  • Slow response in stable materials