Ok, this is where a lot of people get confused. A HDRI image is a HIGH DYNAMIC RANGE IMAGE IE it has an extra level of exposures so that you can change the exposure of an image after it has been taken. Pretty cool. Some of the newer cameras that dish in .raw files have the same features. I believe it has to be 16 bit, but I may be wrong (.raws are anyway) So, to continue, bryce does not understand HDRI images, it can't use luminance channels and thus they have no effect on your final output. In fact, bryce can't even use .hdr files. You have to convert the original HDR image into the LDR counterpart, be it in .tiff .bmp or .jpeg format. Usually you want to overexpose it before doing this. Byce uses the ambient value of a texture to determine the amount of 'shared' color it will bleed on the rest of the objects in your scene. Whites bleed more easily than darks (no true radiosity) because bryce sees them as having a higher ambient value than darker colors. When using a panorama on your sphere, make sure to boolean the sphere first as well, IE make a slightly smaller sphere inside of it and boolean it. This prevents problems with polygon normals and texturing. Your scene will be lit MUCH better by the panorama (on true ambience) when doing this and reflections will be less distorted. You usually don't want to combine the 1000's of lights style with the true ambience HDRI style as the render times will be measured in weeks. It's best to just use a few lights (10) in a small 'halo' up above the image somewhere to get a soft shadow. Hope this helps.