Well, I´ve heard a lot about HDR in the last time, but I never found something, for what do I use HDRI/HDR-Rendering, and how do I set it up?

Thx for your replies
Greatz Michael

Even if I limit the search options to this forum only, I find sufficient material providing the answers to your questions.

Anyway, just a quick overview:
HDRI based lighting is a quick and easy way to achieve realistic light (no other light sources are needed - but obviously you can still use them if you need to) for specific scenes which often contain shiny materials like chrome or carpaint. the reason is that they not only give light to the scene, but also give the materials something to reflect, thus making the scene looking a lot more realistic.

It is somewhat accessible in Blender through AO using the World Texture as “Lightsource” but I’m still not sure if this is real Image based Lighting (IBL).
In Yafray though, you can get the full power of HDRI’s using GI and the .hdr image as a world texture.

I personally love it and often make use of it. It is definitely worth a try.

Well, If you want to use a HDR Image for Image based lightning you need, of course, a HDR Image. A HDR Image is a 360° view of some place which has not only the usual values of a Picture but also stores information on the intensity of the light so it could differentiate a white Piece of paper from, for example, the Sun.
This is propably not exactly right as I’m far from being an expert, but thats what Wikipedia is for:

Anyways, If you wan’t to create your own Lightprobe to recreate the lighting of your Room for example (which would be useful if you tried to put a CG object into a real Photo), you need a digital camera and a reflecting globe (like the ones used to decorate christmas trees), a tutorial and the right Software.
You can use HDR shop http://www.hdrshop.com/ which is free and easy to use and it has good tutorials.

thx for your answers!

another interpretation of HDRI (which literally just means an image map with high color precision) is that you can render your final pictures to HDR or EXR format, both is considered HDR since they can store more than 8bit per RGB channel unlike regular tga/jpeg.

This is useful if you want to do some serious compositing or color correction on image, because HDR allows much more alteration to the image without losing color information.

Yay, that´s cool to know.