Photoresistor sensors are special resistors made of semiconductor materials such as cadmium sulfide or cadmium selenide. Its main parameters are as follows:
(1) Photocurrent and Bright Resistance
Under a certain applied voltage, the current flowing through the photoresistor is called the photocurrent when light is irradiated, and the ratio of the applied voltage to the photocurrent is called the bright resistance, which is usually represented by "100LX".
(2) Dark Current and Dark Resistance
Under a certain applied voltage, the current flowing through the photoresistor sensor is called dark current when there is no light, and the ratio of the applied voltage to the dark current is called the dark resistance, which is usually expressed as "0LX" (use an illuminance meter to measure the intensity of light, and its unit is LX).
Sensitivity refers to the relative change value of the resistance value (dark resistance) when the photoresistor is not irradiated by light and the resistance value (bright resistance) when irradiated by light.
(4) Spectral Response
Spectral response, also known as spectral sensitivity, refers to the sensitivity of a photoresistor under different wavelengths of monochromatic light. If the sensitivity at different wavelengths is plotted as a curve, the spectral response curve can be obtained.
(5) Illumination Characteristics
The illumination characteristic refers to the characteristic that the electrical signal output by the photoresistor changes with the illuminance. It can be seen from the light characteristic curve of the photoresistor that as the light intensity increases, the resistance of the photoresistor begins to drop rapidly. If the light intensity is further increased, the change in resistance value decreases, and then gradually becomes flat. In most cases, this characteristic is nonlinear.
(6) Volt-ampere Characteristic Curve
Under a certain illuminance, the relationship between the voltage and current applied to both ends of the photoresistor is called the volt-ampere characteristic. Under a given bias voltage, the greater the illuminance, the greater the photocurrent. Under a certain illuminance, the greater the applied voltage, the greater the photocurrent, and there is no saturation. But the voltage cannot be increased indefinitely, because any photoresistor is limited by the rated power, the highest working voltage and the rated current. Exceeding the maximum working voltage and maximum rated current may cause permanent damage to the photoresistor.
(7) Temperature Coefficient
The photoelectric effect of photoresistors is greatly affected by temperature. Some photoresistors have higher photoelectric sensitivity at low temperatures, but lower sensitivity at high temperatures.
(8) Rated Power
Rated power refers to the power that the photoresistor is allowed to consume in a certain circuit. When the temperature rises, the consumed power decreases.