look up light leaks in Kerkythea. Try this: @unknownuser said: ""light-leak" is common issue with photon mapping, no matter of render engine. There are means in KT to fight against it, but generally modelling walls as solid should help. Shooting more photons and enabling secondary final gathering should help too. Usually the light-leak problem is specific to a particular scene, so there is no one good solution to it..." Also you might experiment with taking your scene further. Are you going to have windows and sunlight? the problem could be partly fixed anyway with some lighting in the scene.