EV - Exposure Value is a function of shutter speed and aperture only.
LV - Light Value is a measure of the light only.
At ISO 100 these numbers coincide. e.g. for ISO 100, an LV reading of 15 means you should use an EV setting of 15.
At ISO 200, half as much light is needed so an LV reading of 15 will require an EV setting of 16.