![]() ![]() The Photoconductive Cell as a Light SensorĪ Photoconductive light sensor does not produce electricity but simply changes its physical properties when subjected to light energy. Photojunction devices are specifically designed for detector application and light penetration with their spectral response tuned to the wavelength of incident light. Photo-junction Devices – These photodevices are mainly true semiconductor devices such as the photodiode or phototransistor which use light to control the flow of electrons and holes across their PN-junction.The most common photovoltaic material is Selenium used in solar cells. Light energy falls on to two semiconductor materials sandwiched together creating a voltage of approximately 0.5V. Photo-voltaic Cells – These photodevices generate an emf in proportion to the radiant light energy received and is similar in effect to photoconductivity.The most common photoconductive material is Cadmium Sulphide used in LDR photocells. Thus, more light increase the current for a given applied voltage. Photoconductivity results from light hitting a semiconductor material which controls the current flow through it. Photo-conductive Cells – These photodevices vary their electrical resistance when subjected to light.The amount of energy the photons have depends on the frequency of the light and the higher the frequency, the more energy the photons have converting light energy into electrical energy. Photo-emissive Cells – These are photodevices which release free electrons from a light sensitive material such as caesium when struck by a photon of sufficient energy.Photoelectric devices can be grouped into two main categories, those which generate electricity when illuminated, such as Photo-voltaics or Photo-emissives etc, and those which change their electrical properties in some way such as Photo-resistors or Photo-conductors. Light sensors are more commonly known as “Photoelectric Devices” or “Photo Sensors” because the convert light energy (photons) into electricity (electrons). The light sensor is a passive devices that convert this “light energy” whether visible or in the infra-red parts of the spectrum into an electrical signal output. The LabVIEW VI that reads the voltage across the LDR and converts the voltage to lux is called EMANT300 Example LDR.A Light Sensor generates an output signal indicating the intensity of light by measuring the radiant energy that exists in a very narrow range of frequencies basically called “light”, and which ranges in frequency from “Infra-red” to “Visible” up to “Ultraviolet” light spectrum. If a more accurate light intensity measurement is required, we recommend using the Photodiode (see Application Note on Measuring Light Intensity using Photodiode) Table 1: Typical Low Cost LDR Specification Therefore such a low cost LDR is seldom used for measuring light intensity but more for light presence/absence detection. V_įor a low cost LDR, at the same light intensity, the part to part variation in resistance can be as high as 50%. If the LDR connected to 5V through a 3.3K resistor, using the voltage divider rule, the output voltage of the LDR is The relationship between the resistance R L and light intensity Lux for a typical LDR is The resistance of the Light Dependent Resistor (LDR) varies according to the amount of light that falls on it. Measure Light Intensity using Light Dependent Resistor (LDR) Python for Android, Windows, Raspberry Pi, Ubuntu. ![]()
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