This HR 202 Humidity Detection Sensor Module is sensitive to environmental humidity, is generally used to detect ambient humidity by adjusting the potentiometer, for detecting the humidity can change the threshold ( i.e. the humidity control), such as the need to control the ambient humidity of 60% ,then the corresponding module is transferred to the green light and humidity environment , DO high power output when flat, humidity values below this setting, high output, the green light does not shine. Best for measuring the Humidity in air.