I know this is old but I want to help anyone else that comes along looking for this.
The actual bloom of the lights comes from the timecycle files in update/update.rpf/common/data/timecycle.
The files you need to edit are all the weather files so for example w_clear.xml or w_rain.xml.
In these files you need to find the "<postfx_intensity_bloom>" lines. There are two in each file. One is about a third of the way down and the other is near the bottom. I can't remember what either line does but you need to change both.
Edit all the numbers on each line to desired values. I personally prefer to use 0.1000 for all my ones but depending on your visualsettings, I recommend between 0.0500 and 0.2000. I have an example of my one so you can see and copy/paste if you want:
<postfx_intensity_bloom> 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000 0.1000</postfx_intensity_bloom>
You can however edit it according to the time of day. You can see just above the postfx section a set of numbers representing the time of day each value is associated with. Again, I personally prefer to just have it all the same.
So you need to edit both these lines in every weather timecycle file you want to. I did them all but you can do whichever ones you want. Leave the timecycle_mods.xml files alone unless you also want to edit the bloom for in tunnels etc but be careful.
Also it should be obvious. If you want more bloom increase the number, if you want less, decrease it.
If you want to test and edit while in-game I strongly recommend getting the VSReloader mod. It works great. You can edit your visualsettings and timecycle files while in-game, then press F10 and it reloads in your edits so it's way easier to get the right visuals for the game without having to constantly reload the game which takes forever.
Hope that helps people.