Hey Randy...EasyBloom does adjust for cloudy days or unusually sunny days in areas that have been historically cloudy. I will tell you that the longer you let the sensor take measurements the better the results will be. I also want to point out that even "sunny" windows that are south- or west- facing can have deceivingly low light. Full sun is defined by 6 or more hours of direct sunlight. I wouldn't be surprised if you found that your south- or west- facing windows were receiving less than that. My recommendation would be to give it another go, but keep in mind that even the sunniest spots indoors will never receive as much light as a sunny outdoor location. I hope this is helpful. Let me know if you have any further questions. Cheers...Dr. Robby