The Problem

Here's the problem in a nutshell:

• Real-world scenes contain light ranges that exceed a 50,000:1 dynamic range.

• For over a thousand years, media has been limited to around a 300:1 dynamic range.

• So you have a mapping issue: how do you represent light values in a scene using a much more limited set of light values for a particular media?

If you are not careful, you end up with results like this:

You can see the chair but nothing out of the window.

http://www.cybergrain.com/tech/hdr/

(Fyi:I did not right this)