# Sensor grids for Sunlight beam index

I try to compute the Sunlight beam index (SBI). This is an aparture based metric in [m2hrs] by developed Mardaljevic (https://journals.sagepub.com/doi/10.1177/1477153515621486). It contains a cross sectional area of a beam sunlight entering a space.

In this example I would like to compute an annual SBI with a timestep of 15 minutes. To test I try to compute it for 2 hours between 12h and 14h. Because of the cosine effect the view should for each sun position rotated to get the right area of normal illumance on the grid.
The aperture is exactly south orientated.

How do I get the right position and how can I change automaticly rotate the sensor grid plane for each sunposition?

Any suggestions are very welcome! Thanks.

test_rh7_SBI.gh (97.0 KB)
SBI.3dm (67.4 KB)

Hey @Jurrijn ,

I’m not really sure how your question relates to your Grasshopper file since your grasshopper file just has a view-based study and a direct sun hours study. You can always set the direction of the sensors in your sensor grid to be equal to a sun vector created with the LB Sunpath if you need sensors that are facing perpendicular to the sun.

Thank you for your reaction. In the paper of Mardaljevic a way was suggested to transform the views with Xform and than creating grid. I try to calculate the SBI gridbased from the sunlight hours component.

My strategy is find the angle of incidence with help of the azimuth and altitude (LB sunpath) for each time step. Meanwhile HB sunhours compompont calculate if sun hits a gridpoint or not. The grid is on a fixed position on the aperture (vertical). So I want for each time step to calculate the area of gridpoints that are hit and multiply with de cosine of the angle of incidence. So for each hour I want to know the SBI. And to finish to calculate the sum SBI’s to get the annual SBI.

In this updated file you will see the angle of incidence for the aparture. I try to connect them to the sunlighours component but I can’t fix it. Any idea how to do this? Can I get the results in a Temporal map? Thanks in advance!
test_rh7_SBI_final.gh (91.4 KB)

I try still to calculate the annual SBI for Amsterdam for a window of 1 x 1 m (south orientation). The same interval, window size and orientation of Mardaljevic did in his paper ( https://journals.sagepub.com/doi/10.1177/1477153515621486 ) .
He calculated 1927 m2hrs without a reveal. I tried but my result for Amsterdam is much higher 2536 m2hrs. This is strange because Amsterdam is located further north than London.

There might be a problem with the index of my datatree but I can’t see it. (see attachement)
Does anybody know what could be the problem? Thanks for any help!
test_rh7_SBI_LB.gh (64.3 KB)