ISO 5-4:2009 specifies the geometric conditions for the definition of ISO 5 standard reflection density. It also recommends tolerances on geometric conditions that can be used in the design of instruments. The spectral conditions are specified in ISO 5-3.

ISO 5-4:2009 also specifies the requirements for polarization (if that feature is included) and for backing material, and makes recommendations regarding accuracy and linearity.

Although intended primarily for use in the measurement of the reflection characteristics of photographic and graphic arts materials, ISO 5-4:2009 is also applicable to the measurement of these characteristics for other materials.