Maximum operating voltage Particularly as the device is semiconductor based, the maximum operating voltage must be observed.
Typical leaded light dependent resistor What is light dependent resistor, LDR or photoresistor A photoresistor or light dependent resistor is a component that is sensitive to light. Good conductors have a large number of free electrons that can drift in a given direction under the action of a potential difference. This is typically specified at 0 lux, i.
This gives some of them sufficient energy to break free from the crystal lattice so that they can then conduct electricity. An LDR or photoresistor is made any semiconductor material with a high resistance.
Light dependent resistors, LDRs or photoresistors fall into one of two types or categories: Values of the resistance of the LDR may change over many orders of magnitude the value of the resistance falling as the level of light increases. In this way it follows the same convention used for photodiode and phototransistor circuit symbols where arrows are used to show the light falling on these components. The more light that falls on the device, the more electrons are liberated and the greater the level of conductivity, and this results in a lower level of resistance.
Featured articles. Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it.
Dark resistance Dark resistance values will be given for the photoresistor. In order to utilise these components, it is necessary to know something of how an LDR works, which has been explained above. The LDR symbol used in circuits is based around the resistor circuit symbol, but shows the light, in the form of arrows shining on it.
The process is progressive, and as more light shines on the LDR semiconductor, so more electrons are released to conduct electricity and the resistance falls further.
This is the maximum power the device is able to dissipate within a given temperature range.
They can be described by a variety of names from light dependent resistor, LDR, photoresistor, or even photo cell, photocell or photoconductor. A minimum and maximum vale may be given because of the spreads that are likely to be encountered. At one time LDRs were used in photographic light meters, and even now they are still used in a variety of applications where it is necessary to detect light levels.
Insulators with a high resistance have very few free electrons, and therefore it is hard to make the them move and hence a current to flow.
This photoresistor specification details the wavelength of maximum sensitivity.
Derating may be applicable above a certain temperature. Regardless of the type of light dependent resistor or photoresistor, both types exhibit an increase in conductivity or fall in resistance with increasing levels of incident light. As a result, electrons need less energy to transfer to the conduction band because of the smaller energy gap. The resistance under illumination is a key specification is a key parameter for any photoresistor.