I am trying to calculate DGPs for a whole year in hourly values. To calculate vertical illuminate on the eye level (Ev), I considered a small grid in eye level facing to the window and extracted the hourly values of vertical illuminance.
However, when I manually calculate DGPs based on the following equation, I observed DGPs exceeding one.
DGPs = 6.22 × 10−5 * Ev+ 0.184
I have two question:
First, if my assumption of considering a vertical grid is correct?
Second, do I need to define a threshold for high values of illuminance when calculating DGPs based on this formula?
I would be thankful if anyone can guide me in this matter.