Screen Luminance (gain)

Output (lumens) – light loss (%) / screen area (ft^2) * gain = luminance (foot-lamberts)

Image Illuminance

Foot-lamberts = (lumens / screen area) * screen gain

Desired Contrast Ratio

Light output (lumens) = [(ambient light * desired contrast) * surface area] / 0.75 for derating

Measured Contrast Ratio

[La + (p * Lamb)] / [Lb + (p * Lamb)]

La = lumen output of projector divided by the surface area of the screen multiplied by the gain

Lb = display black level

Lamb = ambient light on surface, measured in foot-candles

p = 1.0 (for front projection) or 0.2 (for rear projection)

Minimum Light Output

Lumens = (9 * image area * p * Lamb) / (screen gain – 0.2)