Hello, there are also 6 volts, the 6 volts know how to have the diffusers of the transparent LEDs and the 3 volts are with a cat eye frame, the 3 volts you can light only with the digital diode tester, at 6 volts no, you can polarize with 12 volts in series with a resistance between 330 and 1000ohms turn it on and see if it is around 3 or 6 volts I leave you an easy cheap tool and of great benefits in the workshop, you can test from a led a strip and to the complete backligkt, if you put it in parallel with the tester, you measure a led that turns on and you have the reading that you are asking http://tv.yoreparo.com/plasma_lcd/1680917.html?p=5833971#5833971 luck