Daylight autonomy: individual interior point with too high local illuminance


I am simulating the daylight autonomy for the internal wall surfaces in a few rooms. When looking at the local illuminance values over the year, I have one point which gets much higher illuminances than the surrounding points. This happens on several days in summer, typically around 10 am: 5'000-15'000 lux compared to the surrounding points at about 300 lux. I tried running the simulations with 4 and 6 atmospherical bounces, but get the same pattern.

For me, the most logical reason would be that I have somewhere a gap in the ceiling/roof, though I cannot find any.

Any tips on what else to check or try?

I am assuming that it is not a bug, as the pattern is too consistent when simulating with slightly different parameters, with and without dynamical shading etc.



Tags: autonomy, daylight, illuminance, local

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Hi Sarah,

Its a little tough to say without seeing more of the model details. Can you share your files with us, either on the forum or via

Thank you,


Hi Alstan

Thanks for your reply.

It is a room with 3 rows of 7 roof windows. I have narrowed it down to the daylight passing through one row of 7 windows with NE-orientation. Each of these windows causes one or two "points" on the east-facing wall where the local illuminance peaks.

- The peaks occur 63 to 72 days per year.

- Each peak occurs always at the same time of day, either hour 9.5 or 10.5.

- The peak internal illuminances are at 20-45 % of the exterior horizontal illuminance. Max. direct transmission allowed by geometry (shades+glazing) is 52 %.

- The timing of the peaks corresponds with the orientation of the windows and the solar position.

I think the logical conclusion is that we have direct sunlight passing through the windows at specific solar positions, hitting these points. I am running an extra simulation with a finer grid (0.1 m instead of 0.4 m) in this region to check.



Hi Alstan

We are still not entirely sure what is happening here. I would like to send you the files, with the problem narrowed down to one small nodegroup. The model is quite large, I hope it is ok for you to take a look?



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