Visualisation Problem - Illuminance values of grid analysis and visualisation very different.


Very new to DIVA and grasshopper but i've been through tutorials and managed to get to grips with the programme and have been able to create successful illuminance analysis of a simple room with shading geometry at specified times of the day which is my aim.

However, if I produce an illuminance grid at a specific time of day the results will be greatly different from when I produce a visualisation of the interior and then view the results in false color. 

Is there a difference between the simulations for point based illuminance and the grid analysis illuminance?

Apologies if i'm misunderstanding the use of visualisation.


Tags: Illuminance, Visualisation

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Hello Douglas,

Thank you for the clear description of the issue and the comparison image. I have a couple of followup questions:

  1. Are you rendering the image with the -i option so that illuminance is specifically calculated? Or are you telling the wxfalsecolor program the units are in illuminance?
  2. What is the workplane height for your sensor-based calculation? To do a proper comparison, you would want it to be a very small distance from the floor, perhaps 1mm.

Best regards,

Hi Alstan, thanks for the reply.

Yes, i've been doing to calculations specified for illuminance by placing -i after my parameters and also changes the parameters for both calculations to be the same. 

My work plane height was at 10cm however after lowering my height to 0.01 I am still having the same issue of very different visualisation values. 

Conducting the Test at the same time for both tests, the radiance parameter I have used for each are as follows: 

Illuminance Grid : -ab 2 -ad 1000 -as 20 -ar 300 -aa 0.1    

Visualisation: -ps 8 -pt .15 -pj .6 -dj 0 -ds .5 -dt .5 -dc .25 -dr 0 -dp 64 -st .85 -ab 2 -aa .1 -ar 300 -ad 1000 -as 20 -lr 4 -lw .05 -av 0 0 0 -i

Any idea as to what could be causing the major differences?

Many thanks,


Hi Douglas,

It is odd as with your illuminance grid there appears to be no areas of the direct light coming in. Could you share your Rhino file here or via e-mail to




I have sent the grasshoopper definition and rhino geometry file to your email.

Thanks again.


Hello Douglas,

Thank you for sharing your files. The big issue is that the surface normal of the surface you use to generate your sensor grid faces downward (negative Z). You see this with your vector display component. This means your sensors are facing the ground rather than the ceiling, as they should be. Correcting for this gets much better results.

I sent my updated files to your e-mail.

All the best,


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