UDK Lightmass Tutorial
Sjoerd "Hourences" De Jong, of The Ball fame, has released an illuminating tutorial on using the new UDK Lightmass global illumination feature within Unreal Engine 3, which he has published on his website
The tutorial explains how to illuminate a world with the new UDK feature and goes over such topics as lightmass importance volumes, light emitting objects and advanced Lightmass properties.
Lightmass is the new lighting system in Unreal for calculating realistic static lighting. It is a global illumination lighting renderer that is a lot more powerful than Unreal's old lighting system. As an example, Mirrors Edge made great use of extensive global illumination lighting, and even while that game wasn't built using Lightmass, Lightmass can give near identical results. Another strength of the system is that it will render translucent shadows. A colored stained window will truly cast colored lighting on its surroundings for example. LM is also fairly easy to work with. There are a lot of properties and options, but most are hidden away. Getting a basic scene with lightmass going takes no more than just adding a light and enabling LM
You can read the tutorial HERE