Maximum allowable error (avg illuminance)


I have prepared a grid-based simulation model with 20 grid points. To validate my model, I took two sets of measurement on the floor and 0.87m height. I compared the average illuminance acquired from measurement and simulation. On the floor, I can see an error rate of 10% and for 0.87 m height, 1%. For the measurement, I have used a clear sky condition on the 23rd of November 14:30 to 16:00. My question, what is the maximum allowable error range for such kind of comparison? can anyone comment from own experience? or guide me to the related document?

For your information, here is an overview:

I guess anything in the ballpark of 10% is pretty good.

The validation done work done by John Mardaljevic in 1995 had a deviation of around 6-13%. That research is pretty much the basis for everything that we do in daylighting simulations with Radiance today.
The official CIE standard allows for an error of around 6% (average) to 11% (single point).


Thank you very much @sarith for your input!