I search for solutions in this order: Past Code, Unreal Source, Wiki, BUF, groups.yahoo, google, screaming at monitor. – RegularX

From Unreal Wiki, The Unreal Engine Documentation Site

Screenshots of the bloom effect, showing with and without.

[1]

[2]

[3]

[4]

[5]

[6]

As you can see, the primary effect is that the level is much more brighter, but there is a blur effect around bright parts too.