Which item is used to measure film density as part of a QA program?

• A. Thermometer
• B. Phantom
• C. Densitometer
• D. Light meter

Answer: (C)

Measuring film density in a QA program relies on a device that quantifies how much light is blocked by the developed film. The densitometer does this by directing light through the film and measuring the transmitted light to produce a numerical optical density value. In QA, it’s used with a sensitometry strip or daily density checks to ensure processed film density stays within specified limits, signaling proper exposure, development, and processor performance. If readings drift, it can indicate issues like incorrect developer activity, temperature changes, or exposure technique problems.

A thermometer measures temperature, which influences density but doesn’t quantify it. A phantom is used to assess image quality aspects such as contrast and resolution, not to measure film density. A light meter gauges ambient or exposure-related light, not the film’s density after processing.