How much RAM do you have? You are running out of memory so you should get more RAM or increase virtual memory amount on your system.
i try to build light on my scene.
during the test, the following problems occur:
my spec is 970 and 4790k win 7.
what could be the reason?
You have 8BG. It is enough most of the time but you have a large landscape so consider using dynamic lighting instead.
Hello, this is full spec of my computer.
the scene is not demanding, just a few simple trees, two windmills and a couple of simple buildings
or bulid everytime when i add something?
i never build light for this scene, i have something about 250 obj
With dynamic lighting(movable lights) you dont have to build at all. With static lighting you should build when your level is ready, not every time you place an object. Check out this document for more info: