When or How do i know when it's too much, or very risky for my alternator, electric / electronics devices or even amp/sub/speakers continue playing my songs???
I guess it's normal that lights dim a little bit (with engine in idle)
If you're dropping your battery below 12 volts, you will destroy it, and then it will destroy your alternator. (Unless you're using a deep cycle battery).
If your lights are dimming, you should really consider a HO alternator..it does make quite a bit of difference in the sound quality too, if you're not currently able to supply the power the amps in your ride are demanding.
(Unless you're using a deep cycle battery).