Illuminance meter used like this

An illuminance meter (or lux meter) is an instrument that specifically measures luminosity and brightness. It is to measure the light intensity (illuminance) is the degree to which the object is illuminated, that is, the ratio of the luminous flux on the surface of the object to the illuminated area. The illuminance meter is usually composed of a selenium photovoltaic cell or a silicon photovoltaic cell and a microammeter.
How to use illuminance meter:
1. Turn on the power first.
2. Open the detector cover and place the light detector horizontally on the measuring position.
3. Find a suitable measurement gear.
4. The illuminance meter starts to work and displays the illuminance value on the display.
5. The data displayed on the screen changes constantly. When the displayed data is relatively stable, press the HOLD key (⑧ key) to lock the data.
6. Read and record the observed value displayed in the reader. The observed value is equal to the product of the number displayed in the reader and the range value.
7. Press the lock switch again to cancel the reading lock function.
8. For each observation, read three consecutive times and record.
9. After the measurement is completed, press the power switch to cut off the power.
10. After we use up the illuminance meter, we need to close the light detector cover and put it back in the box.
  Precautions:
1 Photocells use selenium (Se) photovoltaic cells or silicon (Si) photovoltaic cells with good linearity; long-term work can still maintain good stability and high sensitivity; when high E is selected, high internal resistance photovoltaic cells are used, which has low sensitivity and good linearity , It is not easily damaged by strong light.
2. There is a V(λ) correction filter inside, which is suitable for the illuminance of the light source with different color temperature, and the error is small.
3. Add a cosine angle compensator (opal glass or white plastic) before the photocell because the photocell deviates from the cosine law when the incident angle is large.
4. The illuminance meter should work at room temperature or close to room temperature (the drift of the photocell changes with the temperature