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).
The exposure value for a particular film speed is directly proportional to luminance; however, this relationship can vary depending on the reflected-light meter's calibration constant. Most photographic equipment manufacturers typically specify metering sensitivities in EV at ISO 100 (the uppercase 'V' is commonly used).