Mateo: 1. I'm not sure about this. You can vary the quality of Environment Lighting but I don't understand exactly how this works: you'll have to ask Eric to explain. 2. The HDRI engine in C3 doesn't appear to be resolution dependent. It takes the same amount of time to render a HiRes hdr file as a LowRes. Kaom: The main difference between using an HDRI file and a jpg or bmp is the control you have (apart from any differences there might be in the way Carrara uses the files to light the scene). HDRI files have more information - the shadows and highlights have more definition - but it's not all displayed at once; it depends what intensity setting you use. The idea is to approximate how the human eye sees things (and therefore light scenes in a 'natural' way), within the confines of what a monitor can display.