Illuminance meter measurement principle:Photocell is a photoelectric element that converts light energy directly into electrical energy. When light hits the surface of the selenium photocell, the incident light passes through the metal film 4 to reach the dividing surface of the semiconductor selenium layer 2 and the metal film 4, producing a photoelectric effect at the interface. The size of the generated potential difference is proportional to the illumination on the surface of the photocell receiving light. At this point, if an external circuit is connected, a current will pass and the current value is indicated from a microammeter scaled in lux (Lx). The size of the photocurrent depends on the intensity of the incident light and the resistance in the circuit. Illuminance meter has a variable gear device, so you can measure high illumination, but also can measure low illumination. The steps of using the illuminance meter. Turn on the power. Open the light detector cover and place the light detector horizontally in the measuring position.Select the appropriate measurement gear.If the left end of the display only shows 1, indicating that the illuminance is too much, you need to press the range key ( key), adjust the measurement multiplier.The illuminance meter starts to work, and the illuminance value is displayed on the display. Display data on the display constantly change, when the display data is more stable, press HOLD key ( key) to lock the data.Read and record the observation value displayed in the reader. The observed value is equal to the product of the number displayed in the reader and the range value.For example: the screen shows 500, the lower right corner shows the status of 2000, the illuminance measurement value is 1000000lx, that is, (500 2000). Press the lock switch again to cancel the reading value lock function. each observation, three consecutive readings and record. After each measurement is completed, press the power switch key to cut off the power.Cover the lid of the light detector and put it back into the box.