Photodiagnostic testing is a vital tool for diagnosing conditions where the skin is abnormally sensitive to light. Historically, comparing how much ultraviolet (UV) radiation triggers a reaction has been difficult because different light sources and wavelengths produce widely different results when measured in traditional units (mJcm−2). To solve this, we can use the Standard Erythema Dose (SED), a measurement designed to be independent of the specific light source used. Using SED significantly reduces the variation between different wavelengths, allowing doctors to more consistently compare phototesting results with established "normal" ranges regardless of the equipment or the specific centre performing the test. This standardisation leads to more reliable and accurate diagnoses for patients with photosensitivity.
Publication: Quantity of ultraviolet radiation required to produce erythema: normal ranges in phototesting