Super intense light, how can I fix this?

[mindflux]

No worries, too bad there was no easy solution for your problem.

The brightness change after installing Dawnguard and Hearthfire is most likely because your SkyrimPrefs.ini was altered by either of the expansions, but exactly what was changed, I can't say. Decreasing brightness and compensating with ambient lighting will work pretty fine as a solution since particle effects should not be affected by ambient lighting. Just do not decrease brightness too much or will you lose the luminosity of the light sources as well.

[Jellicent]

I have now altered the settings and sadly there were no changes. That probably is because I'm playing in window mode and brightness doesn't affect the game screen. :(
I'll just have to live with it.

[mindflux]

Which settings? Sorry if I was slightly vague, you need to implement brightness control to the post-processing code you're using, PP3 if I remember right.

[Jellicent]

I tried to alter ambient lighting for the day and brightness and gamma. The last two didn't apply because I'm playing in borderless window mode.

And what do you mean with a brightness control? It sounds new to me.