Based on the tutorial material, I learned the way to calculate the illuminance value of the points of the working plane is as follows. The working plane is 0.8 above the floor.
In my case, the lighting sources are white light and the number of points is 1232. I compared the result of Radiance and the result from other commercial software like DIALux Evo and I found that when the value of -ab is 2 or 3 the results of Radiance and the commercial software start to be close. But when -ab=2, it takes more than 4 minutes to get the result, which is too slow for me. Therefore, I would like to ask if there is a faster way to calculate the illuminance of the working plane without changing the number of points and the number of ambient bounces.
The simplest change would be to add a -n option if you are running under Unix, which adds multiple processes to rtrace. This only helps if you have many input points, more than you have processors. For 8 processor cores, you can try:
The rtrace -af option specifies a file to share ambient values, which are shared between rtrace processes. Without this option, the speedup will not be very good. The formula in rcalc is to give you Luminance rather than just the red channel times 179.
Thank you very much for your help. The Accelerad looks is a very powerful tool. Thank you for letting me know about this promising way to accelerate lighting simulation.
Without the option, one processor is always used, and this is all you can use with the Windows version. However, you can use WSL (Windows Subsystem for Linux) to get full multi-processing support from Radiance. I do not know the details of how to do this, but the topic has been raised on the forum here and here.