Define the optical viewing window and opaque union areaMeasure the window the customer actually looks throughGeometric example · not a measured product or optical simulationDefined viewing window1. Draw the window on the optical drawing.2. Count opaque footprints inside it.Include pads, parts and both circuit sides.3. Count overlaps once: use the union area.4. Specify wavelength, angle and haze.A clear area is not a transmission test result.Example: 90% clear area × 90% clear-stack transmission ≈ 81%This area-average proxy does not predict diffraction, reflections or local visibility.Opaque copper and transparent conductive films require different optical models.