We have added a quick comparison of different techniques for lighting an interior through a window in the help index:
Best regards,
Vlado
Vlado…
in that example, do you use a “Skylight Portal” at all?
Nope. Although I could have used it… the result would have been the same.
Best regards,
Vlado
The skylight portal is useful to lock the color of the light to that of the environment, so that you have less colors to adjust…
Best regards,
Vlado
Right, I get it now -- that makes perfect sense. Back when that feature was first introduced, I thought there was something more mystical about it…
I think it’s the word “portal” that threw me off… it has that science-fiction sensibility.
quoted from tutorial:
In this exampe, using a VRayLight produces the best result in the shortest time. However, if you need to have many lights, this method can become quite slow, since every single light needs to be sampled.
so what would be the best approach then? Just skylight?
Yeah, just skylight would be best then. If there are some particular shadows that you want to emphasize, you can use lights just for them.
Best regards,
Vlado
@ percy: Using only skylight without any other lights really makes things very fast although it doesn’t give enough control over the lighting. The fly-through animation in the tutorial had only skylight and rendertimes were below 30s without MBlur.
Dead Link above. Was looking into the use of skylight portals.
thanks 
I’m happy to read this 
!! I already use this method and it work very well.
thx Vlado.
well any vray light at the window would add to render time, because it would need to compute extra samples for it. Imo having any kind of luminarie object in the window is physicly incorrect, that is if we try to achieve physicly correct lighting distribution.
This can be argued… as you can see from the examples on that page, the resulting distribution from all methods, with or without a VRayLight at the window, is the same. Of course, this is true only if there is nothing else outside.
Best regards,
Vlado