Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
I'll start by saying you should be realistic about how close a daylight simulation model and reality can be. Funded validations, where care is taken to measure surface reflectances, and monitor sky conditions, routinely have bias error of up to 15% and RMS error of 30-40%. If you're doing an ad hoc validation, point in time error of 50% or more should be expected.
https://dspace.lboro.ac.uk/dspace-jspui/bitstream/2134/23356/1/Mardaljevic-PhD-2000.pdf https://www.sciencedirect.com/science/article/pii/S0378778801000585
You should know that there are two categories of error. First, model error, which is error related to reflectance and transmittance characteristics and geometry. More effort can help drastically in these cases.
The second source of error is in the representation of the sky. The sky in your simulation will never match reality. Perez skies generated from direct and diffuse measurements are always wrong. Even HDR captured luminance maps will have error of 10% (http://www.ibpsa.org/proceedings/BS2017/BS2017_368.pdf).
If I had to do a quick and dirty validation, I'd use a camera with fisheye lens just outside the window ala Mehlika Inanici (https://faculty.washington.edu/inanici/Publications/mi-luekos2010.pdf) to capture sky and ground contribution to the window. Then I'd use illuminance sensors and maybe a second camera in the space to compare against simulated models.
Good luck!
