What is the meaning of the air quality indicator of Mi Air Purifier and the corresponding relationship of the number in the APP?

Problem Explanation: 
The air quality light of the Mi Air Purifier indicates the current PM2.5 level in the air.
The corresponding relationship between the indicator light and the value displayed in APP is as follows:
Green: 0 ~ 75
Orange: 75 ~ 150
Red: above 150
Notes: 
Users may encounter the following problems:
When the APP value has changed from above 75 to below 75, but the purifier light has not changed from orange to green.
This is a normal phenomenon, which is caused by the buffering algorithm, which is to avoid the bad experience caused by the constant color change of the purifier light at the critical value.