There are two types of lighting that you will need to take into account if you want to create well lit levels—direct and indirect.

Direct light is the one that is coming directly from the source. Indirect light is created by light bouncing off the affected area at a certain angle with variable intensity. In the real world, the number of bounces is infinite and that is the reason why we can see dark areas that don't have light shining directly at them. In computer software, we don't yet have the infinite computing power at our disposal to be able to use different tricks to simulate the realistic lighting at runtime. The process that simulates indirect lighting, light bouncing, reflections, and color bleeding is known as Global Illumination (GI).

Unity 5 is powered by one of the industry's leading technologies for handling indirect lighting (radiosity) in the gaming industry, called Enlighten by Geomerics. Games such as Battlefield 3-4, Medal of Honor: Warfighter, Need for...