This ferrite is optimised for 25 MHz to 2500 MHz frequency and is therefore more suitable for filtering out microwaves on your electricity wires created by mobile phones and other devices working at these frequencies. Light cords that dangle into the room are often at a length where they naturally act as an aerial for the mobile phone frequencies, re-radiating the electromagnetic fields that they pick up back into the house. Clipping this ferrite to the light cord will prevent the vast majority of these signals from going into the wiring, thus reducing the Dirty Electricity. They can also be used on wired Hands Free kits for mobile phones, to lower the fields going up to the earpiece (a better solution would be to use an airtube hands free kit however). Please note that once this ferrite is clipped firmly shut, it is difficult to reopen, so don't clip it shut completely until you are sure it's in the right place. One size fits all. If the diameter of the lighting cable is thin then the hole in the ferrite can be made smaller with cling film or any other suitable non-conductive material.