You can plug any light in (with the right voltage ofc) and it will work.
A Vu-Meter is simply measuring the volume of the sound, the bigger the voltages, the higher the light will go on the bar. :)
Though, getting it accurate takes calibrating and such, and I will not go over that.
This is as simple as it gets, and it's pretty awesome!
Step 1: Gather your parts!
Standard transistor, cheap and easy to find.
Use as many as you want!
Then you need just as many diodes + a few spares. (take note of the Vf drop they have, too high, and you can't use many leds with low voltage)
A pcb board.
a pin-breakable thing :^) -- The same thing you use to build shields with.
A potentiometer (100k for this one) To adjust sensitivity on the bar.
A simple switch.
And last but most important, a lunchbox.