Exposure Value (EV)
A single number describing every combination of aperture and shutter speed that produces the same exposure.
Formula / rule
EV = log₂(N² / t)
Measured in
EV
In depth
EV 0 is defined as f/1 for one second, and each whole number represents one stop. Because the scale collapses two variables into one, it is the natural language for light meters, exposure compensation and dynamic range. When a scene brightness is quoted 'at ISO 100', the EV number tells you directly what settings to use.
Examples in practice
Bright sun on sand or snow sits near EV 16; a candlelit room sits near EV 4 — twelve stops, or a factor of four thousand in light.