For your reference:
Based on ICH Q1B described: The purpose of forced degradation testing studies is to evaluate the overall photosensitivity of the material for method development purposes and/or degradation pathway elucidation.
As long as you can get 5% or more than 5% photo degradants, your “12000LX,延长光照的时间” will be fine to help your “method development purposes and/or degradation pathway elucidation”.