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Is using Photon Number Multiplier for lights has any meaning when using Lightmap mode?
Im getting 1-2 bright spots quite often when using Lightmap mode. They looks like "lost" high power photons. Can't track down what causes these, so i have to re-render image few times untill these spots are gone. Seems like they seen or reflective surfaces mostly.

No. Number multiplier works only in Photon map. In Lightmap the photons are distributed based on camera view so it doesn't suffer from the problems Photon map has.

Is this related to the other problem you posted before?

No it's not related to Photonmap problem:)
Looks like very high energy photons get bounced from objects that are close to light.
Reducing light intensity near a light source by changing it's falloff to inv. dist^1 instead of inv. dist^2 helps to get rid of splotches or at least reduce their number dramatically. There's an image with photon estimate for both cases. So i think that was a problem.
Is there any other way to "cut off" these photons expt balancing light position and intencity? Maybe some sort of iimiting dynamic range?
In some cases i dont get enough of direct light and inv.dist^1 leads to more "flat" lighting.

Ah.. Yes there's an extraordinary shader tool called "Krayindirectrays".
This can only be applied to luminous surfaces though. I havent tested this but if you are using very intensive lights close to other geometry you can probably try to apply the shader to those nearby surfaces and see if you can limit the dynamics.
It is possible to set the "cutoff/limitdr range at a higher value than 100% so you get the surface more intense before it starts to limit the range if you want.
Try 300-1000% to see the difference. When you use LimitDR applied to a luminous surface you dont need as many Finalgather rays as you would need to get a clean image without LimitDR applied. Also good to know is that Reflections does NOT get cut off from a surface with LimitDR applied, they will look as intense as usual but lightdistribution will be softer and more controlled.

Leftover wrote:No it's not related to Photonmap problem:)
Looks like very high energy photons get bounced from objects that are close to light.
Reducing light intensity near a light source by changing it's falloff to inv. dist^1 instead of inv. dist^2 helps to get rid of splotches or at least reduce their number dramatically. There's an image with photon estimate for both cases. So i think that was a problem.
Is there any other way to "cut off" these photons expt balancing light position and intencity? Maybe some sort of iimiting dynamic range?
In some cases i dont get enough of direct light and inv.dist^1 leads to more "flat" lighting.

Could you send me your scene so I can check it out?

I made simple test scene for you. Do 2-3 renders and you will get some of these splotches. Im sure they related to "heavy" lit surfaces close to light.

I will ask G. about this. However there is something you can do to fix this: if you notice the number of cells is very high in your precompute. This means that the cells are very small and may contain too little photons which are very bright in some part. To overcome this turn off Auto GI mode and hand tweak the Gi resolution until you get to about 40.0000-50.000 cells.

Also - I see that area light is very close to some furniture - this may cause problem because the area light photons are hiting the furniture directly and bouncing off with great intensity to some weird places. Perhaps it would help if you put your area light outside the window about 1m away and make it about 3/4 size of a window.

I used low N to make spots more noticeable. And yes that's what i was talking about, objects close to light cause this problem. Setting Intensity falloff to Inverse Distance^1 helps as well.