For a given film speed, exposure value is directly related to luminance, although the relationship depends on the reflected-light meter calibration constant . Most photographic equipment manufacturers specify metering sensitivities in EV at ISO 100 speed (the uppercase 'V' is almost universal).
For a consistent film sensitivity level, exposure value correlates with luminance, although this correlation may differ based on the reflected-light meter's calibration factor. Many photography device producers define metering sensitivities using EV at ISO 100 speed (uppercase 'V' is prevalent).