justpatrick, in a nutshell, HDRI & LDRI are the lighting information, how the environment & everything in it reacts to the light. HDRI records "all" of the available light information, which can then be used to recreate the lighting in a virtual atmosphere, changing brightness etc, accuratly & if the system allows for it, in real time. The IBL /LDRI only records a limited amount of light info, but with additional manipulation, can achieve the "look" of an HDRI scene. The advantage is that with HDRI It's "easier" to accuratly get your scene looking like it does in the "real world", & intergrate virtual & "real" elements together. http://www.debevec.org/ one of the best resources for HDRI & IBL/ Global Illumination work straight from the proverbial horses mouth :-)