You guys should be nice.

HDR stands for High Dynmaic Range lighting - and is a technique that allows for the storage of a much wider range of light values than a typical 24-bit image. Cameras are very limited by how much contrast range they can capture - with HDR lighting you can assemble a series of photos taken at different exposures to create a HDR image - there are different formats for this, and like all image formats there is competition to define an HDR standard.

More than dynamic range - HDR has come to be associated with light probes and capturing light in a 360 degree panorma. This can acurately represent the lighting in a scene, light that comes from all directions in real life. An added benefit, is that this 360 degree panoramic HDR image can be used for environment reflections. The results - as seen above can be quite stunning. There is an effort to implement HDR lighting in games - and should provide for some very interesting possibilities.

This is at least how I understand it. Someone with more knowledge might be able to clarify it a bit.

This technique of the volumetric lights in trees has me stumped as well. When I first saw it I think I sat there for an hour trying to figure it out. Maybe it is just models that are coded to point towards the sun, or sprites somehow, or???

Maybe a game guru can help us out!