there is a SWEET FREE ap to let you preview and look at radiance values.. called HDRview
the download is a zip 3rd 4th paragraph down on this linked page..
Its just the HDRview.exe zipped.. at least thats hows ive had it for years.. and I but that in my c:progrmafiles directory..
I right click on a .hdr image and say open with>choose program... and the BROWSE to the programfiles directory selecthe the hdrview.exe AND MAKE SURE TO CHECK: always USE the selected program to open this kind of file (in the open with window)
now everytime i double ckil an .hdr it opens it quick with hdrview.exe...
AND you can mouse over parts of your .hdr image and On the TOP left of the WINDow will give you readouts.. of your pixwel location.. and MOST important your color info for that pixel.. inthe streetatdawn.hdr the sun is a value of 21,000.00 15,000.00 11,000.00 !!! wow thats intense.. basically you WANT the sun to be as much over the value of 1.00 as possible the brighter the better for sharp shadows..
the hdr you posted looked like the sun was only in the 1.0 range.. the image looks super flat. and maybe that why your not getting sharp shadows..
also with HDRview.. you can use the "+" and "-" keys on your keyboard to go up/down in expoure as weel as other shortcuts explaing inthe html abover.. (or right click on .hdr image and it will give you options.. like zoom in out) you pan your image by ckicking and draging it..
-hope this helps