led - How to drop the external source output voltage using Arduino

I would like to connect the 10VDC of my LED driver to Arduino so I can dim the lights.

I've found out that the lower the output voltage, the more I am able to dim the LED lights.

My question is, how can i control/lower the output voltage of external 10Vdc using arduino.

Note: I don't like to use photo-resistor because I wanted to manually control the dim light by entering some value on arduino TX/RX.

UPDATE: The 10Vdc were specially provided by the LED Driver for the purpose of dimming the LED.