Vertical illuminance at eye level


I am trying to calculate DGPs for a whole year in hourly values in DIVA for Grasshopper. 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.


Did you find any answer regarding the grid? In order to have vertical illuminance at eye level for many positions, do i have to create many small vertical grids for each position around the space?