By default, daylight is included in radiosity calculations, even for indoor scenes (light can come through a window). You can turn daylight off if you want. This basically omits daylight from the lighting calculations, and can speed up rendering.
Note: The Enable Daylight option should always remain on for exterior shots, even if it is a night shot. If you want to create a night shot, change your time of day instead.
To turn daylight off:
Select View
> 3DTrueView > 3DTrueView Options, or click the 3DTrueView
Options button on the 3DTrueView toolbar.
In the Program Settings dialog, select the Rendering tab.
Uncheck the Enable Daylight check box.
Click OK.