Hi Guys,

My simulations take too much time (6hours). Is there a way to reduce the number of ray that Radiance simulate? Ot any other way to speed up he process even if it means less accurate result?

I am using these parameters maybe I can change some of the resolution:

-ab 3 -aa .1 -ar 500 -ad 1024 -as 512 -i

Many thanks,


Tags: speed, time

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Hard to say anything without knowing your scene, but in my opinion -ab 3 can already be low, e.g. if you have deep daylight penetration into a space and high(er) reflectance materials. You could decrease the -ar and -aa values (say, 300 ar), but you must make sure the resulting interpolation does not become smaller than the minimum aperture sizes you are dealing with. -ad and -as are culprits, too; you could go down with the -ad to 512, but your results might become way blotchy. Also, reduce node spacing and/or split the sim file into simultaneous runs. Imho 6 hours are.. not unheard of.



Hi Max, 

Thanks a lot for your reply.

I am not using any daylight, simulating IES light in a box. I've tried the following which seems to work well:

-ab 1 -aa .1 -ar 100 -ad 50 -as 50 -i

Is it a bit exagerated?

All the best,


I'd say those are really low settings; the 1 ab only will probably not give you a very realistic light interreflection. One good method to check for how things might look is to run an image-based metric (sorry if you are doing that already) and observe how the image degrades- if it doesn't "look right", then usually the numeric output via rtrace won't be very much spot on, either.

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