Abstract: An open area photometer for determining the amount of light energy dissipated when a light source of known intensity is passed through a light restricting test specimen. The photometer includes a light source whose intensity level is established by an adjustable shutter positioned in front of the light source, a light diffusing element positioned between the shutter and a fresnel lens, a field effect phototransistor whose output is monitored on a micro-ammeter and a housing confining the components to prevent unwanted light loss. The specimen is positioned between the lens and the light diffusing element.