If your taillights look like you have your foot on the brake at all times,then they are too bright.If there is not enough "difference" between the brake light being on & the turnsignal being able to be seen,this too is a problem.ANd if your taillights are too dim to be seen in day light,you need to FIX them first.If you want to go brighter,later-tehn fine.But just tossing in LEDs is nothing but a band-aid solution.
There may be no issues at all.Hence,i used the phrse "CHECK FIRST".