In the left image, the room is rendered almost noise free. In the right, lots of instances of the same point light were created, and the noise is very much.
I understand that more light implies more render time, because there are more players for Cycles to take care of, but…
do you know how could I set this scene so that the number of Lamps does not influence so much the noise? I mean: what if i need to set up an urban scene where there many street lights, for example?
This is just a problem with path tracers in general. Arnold recently got an update for things like large city scenes that DRASTICALLY reduces render time (17 hours to 1.5 in the example from their release notes). It involves throwing away lights from the sample list based on distance and strength, but beyond that I don’t know how it was done. Hopefully we’ll see such an improvement in Cycles at some point in the future as well, but until then many-light scenes will be a problem.
I have been told that point lights are noisier than mesh lamps (because all rays have the same origin). This was a few versions back on Cycles. You may want to convert your point lamps to mesh planes and conduct the test again. Also try a Light Falloff node in front of the Emission. Turn on Most Important Sampling as well.
