I'm a french Sustainable Building Engineer and i'm often working on natural light simulations with IESve Radiance.
My questioning is about the number of ambient bounces allowed in IESve Radiance costumize parameters.
In some projects where the french ceritfication (HQE) is used, we hardly meet the very low and minimal requirements (A daylight factor of 0.7 on a zone that goes more or less 4 meters deep in the room). In fact, when the customise parameters are set to default (3 ambient bounces) the result seems quite pessimistic compare to other simulation tools. The temptation is then to increase the number of ambient bounces to improve the results (and get closer to reality measurements) but a previous answer to an older post said:
Going to 4 ambient bounces doesn't seems to be enough in heavy masked scenes and we usually go to 6 or even 8 ambient bounces in order to prevent too much glazed facade.I spoke with one of our Radiance users in the Support Team here and the resounding advice was never to go to 8 ambient bounces. 4 seems to be the standard upper limit, I don't really know if 8 isn't allowed (I mean Radiance allows it) but it does seem to be the point where things become unpredictable at least.
Then my questions are:
Why, where Radiance can go to 8 bounces, the IESve support does not advise to go to the maximum 8 bounces?
And even if the recommandations are not respected, what is the risk and does the physic model and the results remains valid? (Every simulations we did with 6 or 8 ambient bounces went fine and gave reasonnable results).
I'm really hoping to be finally set on this question which make a big debate in my company. Any help will be great.
Regards,
Eloi.