The current flowing through the resistance of the photoresistor in the dark is called the dark current, and the current flowing in the resistor when it is bright is called the bright current.
The relationship between the photocurrent of the photoresistor and the light intensity is called the light characteristics of the photoresistor. Different types of photoresistors have different illumination characteristics.
Since the light characteristic curve of the photoresistor is not a straight line, it is not used as a linear measuring element in the application, which is also its defect. It is often used as a switch-type photoelectric signal sensor element in automatic control systems.
The sensitivity of photoresistors to light of different wavelengths is different. The spectral response peak of the cadmium sulfide photoresistor is in the visible light region, while the peak of lead sulfide is in the infrared region. Therefore, the combination with the light source should be considered in the application to get better results.
After the photoresistor is exposed to light, the photoelectric sensor needs a certain rising delay time to reach a stable value. Similarly, when the light is stopped, the photocurrent also needs a certain falling delay time to reach the value of the dark current, which is the delay characteristic of the photoresistor.