valokohtavalosensorissa

A valokohtavalosensorissa, often translated as a light-dependent resistor (LDR) or photoresistor, is a passive electronic component whose electrical resistance decreases with increasing incident light intensity. In simpler terms, it gets more conductive when more light shines on it. This property makes it useful for light-sensing applications.

The core of an LDR is typically made of a semiconductor material, such as cadmium sulfide (CdS) or cadmium selenide (CdSe). When photons strike the semiconductor material, they excite electrons, creating free charge carriers. The more photons there are, the more charge carriers are generated, leading to a lower resistance. Conversely, in the absence of light, the resistance is very high.

LDRs are commonly used in simple light-activated circuits. For instance, they can be found in automatic streetlights that turn on when it gets dark, or in night lights that activate at dusk. They can also be used in light meters, alarms, and simple automation systems where detecting the presence or absence of light is required. Their low cost and ease of use make them a popular choice for many hobbyist and educational projects. However, LDRs are not known for their speed or precise accuracy; they have a relatively slow response time and their resistance can vary with temperature. For applications requiring high precision or rapid light detection, photodiodes or phototransistors are often preferred.