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Exposure Value (EV) and Light Measurement Science
In photography, Exposure Value (EV) is a logarithmic scale representing combinations of camera shutter speed and lens aperture that yield equivalent exposures. The formula for EV at a given setting is: \(EV = \log_2 \left( \frac{N^2}{t} \right)\), where \(N\) is the f-number (aperture) and \(t\) is the shutter speed in seconds.
To compare lighting conditions independent of ISO, the values are normalized to ISO 100, known as EV100: \(EV_{100} = EV - \log_2 \left( \frac{\text{ISO}}{100} \right)\). For example, bright direct sunlight corresponds to EV100 = 15 (which aligns with the "Sunny 16" rule: f/16 aperture with a shutter speed equal to 1/ISO). Indoor lighting is typically around EV100 = 5 to 7.