Hello caohuongls,
Thanks for the question.
Unfortunately you have provided no code showing what you have done so far so I’m going to do a little guessing.
If you have used a numeric_state trigger you have a parameter there called for: I suggest you use that and set it so that the light level you want is checked to be stable about 4x longer than you think you might need, so like 5 minutes maybe. That should give you a more stable reading.