Exposure Index Calculator

Formula

The formula to calculate the Exposure Index (EI) is:

\[ EI = \frac{L \times T \times ISO}{A^2} \]

Where:

\(EI\) is the Exposure Index
\(L\) is the Luminance of the scene (cd/m²)
\(T\) is the Exposure Time (s)
\(ISO\) is the Sensitivity of the Camera Sensor (ISO value)
\(A\) is the Aperture of the Lens (f-number)

What is an Exposure Index?

Exposure Index (EI) is a numerical representation used in photography to indicate a combination of aperture size and shutter speed in a camera. It is used to measure the amount of light that reaches the film or image sensor. The higher the EI, the more sensitive the film or sensor is to light, allowing for better images in low-light conditions. EI is part of the ISO system, which is a standard for film speed or sensor sensitivity.

Example Calculation

Let's assume the following values for an example:

Luminance (L) = 500 cd/m²
Exposure Time (T) = 0.01 s
ISO Sensitivity (ISO) = 400
Aperture (A) = 2.8

Using the formula:

\[ EI = \frac{500 \times 0.01 \times 400}{2.8^2} \approx 25.51 \]

The Exposure Index is approximately 25.51.