A photoresistor is simply a resistor whose resistance depends on the amount of light incidentupon it. Photoresistors are used to make light-sensitive devices, and are often made from cadmium sulfide (CdS). The resistance of a CdS photoresistor varies inversely to the amount of light incident upon it. In other words, its resistance will be higher at low light levels (in the dark) and lower at high light levels (in the light).
How A Photoresistor Works
Photoresistors are made of highly resistant semiconductors that are sensitive to high photonic frequencies, with a photon being a particle of light. As photons come in contact with the semiconductor, they cause electrons that were otherwise bound to the metal to jump to another piece of the semiconductor. As more photons hit the semiconductor, more electrons are knocked loose. This creates a very effective conductive flow of electricity that only travels through the semiconductor when in the presence of light.
Applications
Photoresistors are used for a wide variety of purposes, all of which require light to determine whether a device should be on, off, or set to a particular position. Photoresistors are responsible for turning street lights on and off, measuring the amount of light that is seen by a camera, some types of alarms, and some types of clocks. Photoresistors are also used in dynamic compressors to control gain reduction and can also be calibrated to respond to infrared light.
Advantages
Photoresistors have several important advantages that separate them from other devices. For example, photoresistors are completely dependent on how much light they receive, meaning that external forces will not interfere with the devices that they are connected to. A photoresistor is also very simple because it is only a semiconductor with a conductive pathway connected to one end in order to transfer a current from the semiconductor to an external device that it is powering.
Disadvantages
There are different types of photoresistors and each have their own disadvantages but there are several that they all have in common. For example, most photoresistors cannot detect low levels of light and may not work in certain conditions or circumstances. Photoresistors are also slow to respond to new levels of light and may take up to several seconds to recognize the change. This is because electrons are momentarily still moving through the semiconductor and take a few seconds to calm down or speed up.
Please see this post also : http://theonlinetutorials.com/what-is-a-phototransistor-and-how-it-works.html
Not Satisfied ? Just search & get the result
Related posts:
