Although LV is often confused as being the same as EV, the two are in fact very different. LV is a numerical scale used to judge an absolute level of light in a given scene, while EV measures how much of the light from that scene is allowed into the camera. EV is simply a shorthand way of combining shutter speed and aperture setting and does not specify an absolute measure of light intensity. For that you have to include ISO. EV15 is f16 at 1/125 or f11 at 1/250, etc. regardless of the light level or the film speed.

Numerical scales of LV and EV can be used to measure amount of light and exposure respectively. The EV and LV scales are the same at ISO 100, but if you use a different speed film the EV has to change, whereas LV remains constant. Sunny 16 at ISO 100 is EV 15, but at ISO 400 it’s EV 17, which can get confusing. Sunny 16 is always LV 15 regardless of shutter speed, aperture or ISO. We find it easier to deal in LV.