HDRI environment mapping:

The word inside a sphere - simulated environment.
A HDRI - High Dynamic Range Image can be used instead of light_source and ambient light settings. These type of images contain 32 bit per color pixel and this is much more detailed information than normal images, which usually use 8 bit per color pixel. This means that the bright parts are brighter, the dark parts are darker and there is much more variance in between.
A light probe image is a high dynamic range image of the illumination conditions at a point in space! Each light probe image represents a full 360 × 360 degrees, or 4pi steradians.
Such images can be used to illuminate rendering scenes with image-based lighting.
Sure this is only another "cheap and dirty trick" for "real" raytracing fans, because is simulates an environment that not really there! But have a short look at the sample images here: You'll see - the effect is fantastic!
 
Since version 3.7 POV-Ray supports HDRI (with the extention .hdr) .

It's a good idea also to use radiosity for hdr images to get a full realistic look. For radiosity and hdr illumination we need to set the finish components ambient and diffuse to zero. So it is a good idea not to define ambient and diffuse in any textures used in our scenes, but declare it generally as a default.
All normal light sources should be dimmed down, only some flashlight to light up the shadows should be used with hdr images - remember the hdr image makes the light in the scene!
For HDRI illumination we have to declare:

// hdr environment ----------------------- sky_sphere{ pigment{ image_map{ hdr "building_probe.hdr" gamma 1.1 map_type 1 interpolate 2} }// end pigment rotate <0,40,0> // } // end sphere with hdr image -----------

Updated 23-Nov-2013 for POV-Ray 3.7.0 !

Samples on HDRI high dynamic range images or light probe images you can find here:
Light Probe Image Gallery by Paul E. Debevec (en, es).

HDRI sample 1
Click on the image for a higher resolution!
HDRI probe angular map used here

POV-Ray scene 2 without HDRI illumination

POV-Ray scene 2 with HDRI illumination
Click on the image for a higher resolution!

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