Global Illumination

For GI , there are many setting to explore and to get different results.
At first , I was testing the Accuracy inside the GI attribute, after then is the Radius of the photons.
After confirm the Radius of the photos is good enough for the interior. The Merge Distance inside the setting also will affect the result.

Above images is the progress of testing GI
first image is the radius setting. The default radius setting is 0, I have to make it 0.1 to see the photons cover the interior. If  I enlarge the number to bigger, and i get the 2nd image result.

After that, I put the radius back to 0.1, and then I edit the merge distance. For the merge distance 0, the light photons will be more on the windows which is where is the light comes from.
Next, I slowly to increase the merge distance number , and the the whole interior have the nice and balance photons.Which is the 3rd image I have got.

In conclusion, Radius, Merge Distance and also Accuracy are works together .
and the end result I've got is the image below.