This is the cheapest way to convert the plug on the 220/240V power cord coming out of your ballast or other equipment to a 110/120V style plug. Since the only difference between 120V and 240V cords is the plug and not the actual wire or the wire gauge, this is a very simple solution. However, please note that this does not change the voltage of your equipment; if you're equipment is designed to run only at 240V then the outlet you plug it into must still supply 240v power, and if it's designed to use only 120V power then your outlet must supply 120V power.