The bloom module is, in fact, modifying each of the frames that FS9 (or FSX)  draws. The bloom "hacks" DirectX9, it sets itself in between DirectX9 and your sim silently, in order to "alter" the visuals produced by the sim. This is called "post-processing".

You can deeply alter the effects by editing the content of the file enbseries.ini.

I would also suggest you to give a try to my actual settings. I have stored everything (well, two files, that is) in this archive on my personnal webspace: http://sapdaube.free.fr/fsx/bloom2.zip

There is also another set of files that are tweaked by the talented guys from REX team, but I cannot locate it at the moment. They have some settings which seem to be quite appreciated by a good part of the community.

The effects of the bloom module are not only limited to daytime. The bloom is this kind of "glow" around the shiny parts of a dark picture. Because of this, the flights at dusk or dawn can become very spectacular, and if you have a plane with a sun panel (dark transparent movable thing, I don't know the exact name), you might have to use it sometimes. The results at night, if the module is configured properly, can be quite interesting as well. You'll have to reconsider your usage of cockpit lights, because they might become a real interference to your external vision.

All these things are small details, but they eventually add some immersion in the sim, some additionnal things that make you feel there.

Funny, We've been in continuous sunshine since mid January. Today it rained a about an inch or two. Yikes.