Overview
SIST ISO 80000-7:2020 - Quantities and units - Part 7: Light and radiation defines standardized names, symbols, definitions and units for quantities used in light, optical radiation and associated radiometric and photometric measurements. It covers the wavelength range of approximately 1 nm to 1 mm and, where appropriate, provides conversion factors. The part is one element of the ISO 80000 series on quantities and units and clarifies spectral and directional definitions used in radiometry, photometry and photon measurements.
Key topics and technical requirements
- Scope and purpose: Standardizes quantities and units for electromagnetic radiation in the optical range (≈1 nm–1 mm). No normative references are required in the document.
- Radiometric and photometric quantities: Definitions for fundamental quantities such as radiant energy, radiant flux (power), radiant intensity, radiance, irradiance, and their spectral counterparts (e.g., spectral radiant flux Φλ, spectral radiance Lλ).
- Spectral quantities and reference variables: Spectral quantities are defined with respect to frequency (ν), angular frequency (ω), wavelength in vacuum or medium (λ), and wavenumber (σ). The standard explains relationships between these reference quantities and how spectral densities transform.
- Notation and subscripts: Use of subscripts and symbol conventions to distinguish energetic (subscript e), visible/photometric (subscript v), and photon (subscript p) quantities when needed.
- Directional and derivative definitions: Multidimensional quantities (e.g., radiance L(x,y,θ,φ)) are defined as derivatives (densities) at a point and direction; spectral quantities are formalized as derivatives with respect to wavelength or frequency.
- Optical material parameters: Definition and expression of refractive index including complex refractive index n = n + ik and dependence on frequency, polarization and direction.
- Vision regimes: Definitions and treatment of photopic, scotopic and mesopic luminous quantities, including reference to standard spectral luminous efficiency functions and typical luminous efficacy values (e.g., the 683 lm·W−1 photopic relation noted in the standard).
- Units retained: SI units are used; steradian is retained for solid angle in photometry/radiometry.
Practical applications and who uses it
SIST ISO 80000-7:2020 is essential for:
- Metrologists and national measurement institutes standardizing optical measurements
- Optical and lighting engineers specifying radiometric/photometric performance of lamps, LEDs and displays
- Instrument manufacturers (radiometers, spectroradiometers, photometers) ensuring consistent unit definitions and spectral reporting
- Researchers in vision science, photobiology and optical materials who need unambiguous spectral definitions
- Standards developers, regulators and testing laboratories that require interoperable, traceable measurement terminology
Benefits include improved clarity in measurement reports, consistent labeling of spectral data (λ, ν, σ), and reliable conversion between radiometric, photometric and photon-based quantities.
Related standards and resources
Keywords: SIST ISO 80000-7:2020, quantities and units, light and radiation, radiometry, photometry, spectral radiance, radiant flux, refractive index, photopic scotopic mesopic.
