Overview
ISO 80000-7:2008 (Quantities and units - Part 7: Light) is an international standard that defines the names, symbols and definitions of quantities and units used for light and other electromagnetic radiation. It organizes radiometric, photometric and related optical quantities, recommends SI and accepted non‑SI units, and gives conversion factors and normative references where appropriate. The standard is part of the ISO/IEC 80000 series on quantities and units.
Key topics
- Scope and structure: systematic tables presenting quantities (left pages) and corresponding units (right pages), with definitions, symbols and remarks.
- Radiant vs luminous vs photon quantities: distinction and convention to use subscripts (e, v, p) when needed.
- Spectral quantities and reference variables: definitions using frequency (ν), angular frequency (ω), wavelength (λ), vacuum wavelength (λ0), and wavenumber (σ, ν̃); relationships such as dq = q(ν)dν = q(λ)dλ and conversion relations q(ν) = 2π q(ω) = q(ν̃)/c = q(λ) c/n = q(σ) n/c.
- Optical constants and derived quantities: frequency, wavelength (vacuum and in-medium), wavenumber, refractive index and speed of light conventions.
- Photopic and scotopic photometry: inclusion of standard spectral luminous‑efficiency functions (photopic V(λ) and scotopic V′(λ)), and reference values such as the photopic luminous efficacy constant (683 lm/W) and the scotopic order of magnitude (~1 700 lm/W).
- Units and SI usage: recommendation to use coherent SI units first, presentation of accepted non‑SI units and conversion factors, treatment of dimensionless quantities (unit 1), and use of radian and steradian for convenience.
- Notation and uncertainty: standardized use of symbols (=, ≈, :=) and recommended notation for reporting measurement uncertainty.
Applications
ISO 80000-7 is practical for any activity that needs consistent, internationally harmonized definitions of optical quantities and units:
- Calibration and specification of photometric and radiometric instruments (radiometers, spectroradiometers, luxmeters).
- Lighting design, lamp and luminaire specification, and daylighting analysis.
- Optical and spectroscopic measurement procedures, sensor design and testing.
- Metrology labs, product standards, and regulatory compliance where precise unit definitions and conversions are required.
Who uses this standard
- Metrologists and calibration laboratories
- Optical, lighting and sensor engineers
- Photometry and radiometry specialists
- Standards committees, regulators and test houses
- Researchers in optics, spectroscopy and color science
Related standards
- ISO 80000 series (Parts 1, 3–6, 8–12) and IEC 80000-6 (Electromagnetism) - referenced for space/time, mechanics, thermodynamics and electromagnetism conventions used alongside ISO 80000-7.
