With some lightning objects, it is possible to configure the brightness. Let's say you've added some lamps, and in the render preview see that those lamps are just too bright. They're outshining other items in your room. Like this:

No need to worry, it can be pretty easily fixed. Open the editing menu of the lamp and darken a colour a bit. Like that:

Create a draft render first to check if the brightness level has been decreased to the level you like. If everything's okay, you can now create a proper HD render of your design!