The panel on the front lights up in about 4 different sections, from the base of the hand to the full picture. See the attached pictures; one half lit up, the other fully lit. The battery compartment, located in a little pocket inside the shirt, has an on/off switch, and a little knob for adjusting its sensitivity to sound. At its highest sensitivity, it reacts to the sound of your voice; at its lowest, it'd work perfectly in a loud disco, I'd reckon.
I haven't had to wash it yet, so I don't know how easy this is. The batteries and cable are easily removed, but the EL panel itself is held on with self-adhesive. I'd guess there are only so many times you can remove it before the adhesive stops working. However, for €15, with free delivery, it's pretty good value, and was worth the wait!