Another demo. I placed a 100% mirrored square behind the balls so we can simultaneously see the outdoor scene at full luminence and at the reduced luminence caused by the lower amount of reflection in the spheres.

The mirror, trying to render the full range, is clipped at the maximum luminence of your monitor, which is 1.0. We can only make out a couple details - most of it is above 1 and is a wash of white. However, the interior, which we can see behind all the spheres and mirror, is perfectly lit and rendered well within the unit range 0 to 1.

The reflections in the spheres show plenty of detail, demonstrating that the exterior data is there in the HDR image. It is available for calculations, particularly those involving reflections from imperfect mirror surfaces, where the detail will reveal itself.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)