opegl : Scene is dark

thanks in advance for the help that you can give me.
Let me explain the problem quickly:
I have used the library ASSIMP (3.0) and Devil to import a 3D model in my OpenGL project.
The problem is generated when loading 3ds files, just load the model, the scene is rendered bright, but after 2 seconds it becomes dark. The thing does not happen if I load a file collade (dae): the scene remains clear and bright.

Can you help me understand how it happens?

We will need a bit more detail. Are you moving the camera around the view? If so, you might have a backfaces being culled with the obj.