ISO 9050:2003

Overview

ISO 9050:2003 - "Glass in building - Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors" - specifies standardized methods to measure and calculate how glazing transmits and reflects light and solar energy. It applies to conventional and solar‑control glazing, single, double and triple units, and most transparent materials (with noted exceptions for materials that transmit significantly in the 5 µm–50 µm region). Results support daylighting, heating and ventilation calculations and allow comparison between glazing products.

Key topics and technical requirements

• Measured and calculated parameters
  • Spectral transmittance and reflectance (spectral range stated in the standard)
  • Light transmittance (τv) and external/internal light reflectance (ρv,o / ρv,i) using illuminant D65 and photopic V(λ)
  • Solar direct transmittance, total solar energy transmittance (solar factor, g), UV transmittance (τUV)
  • Colour rendering index, CIE damage factor and skin damage factor
• Measurement conditions
  • Quasi‑parallel, near‑normal incidence (beam axis within 10° of surface normal; individual rays within 5°)
  • Use of spectrophotometers and integrating spheres for diffuse samples
  • Calibration and verification of wavelength and photometric linearity using reference materials
  • Recommended measurement accuracy (transmittance/reflectance reproducibility around ±0.01)
• Calculation procedures
  • Formulae for single, double and triple glazing; general methods for units with more components (Annex A)
  • Spectral data of individual components must be used when calculating multiple glazing performance
  • Guidance on handling diffusing, wedged or thick samples to avoid systematic errors

Practical applications and users

ISO 9050:2003 is used by:

• Glass manufacturers and coating suppliers to document performance data and compare products
• Fenestration and façade engineers performing daylighting, thermal and solar gain calculations
• Architects and building services designers specifying glazing for comfort, energy efficiency and solar control
• Testing laboratories and certification bodies producing standardized test reports for product data sheets
• Researchers analysing solar control, UV protection and daylighting impacts

Using ISO 9050 helps ensure consistent, comparable glazing data for energy modeling, compliance, product selection and specification.

Related standards

• ISO 9845‑1 (reference solar spectral irradiance)
• ISO 10291 / 10292 / 10293 (thermal transmittance and U‑value methods)
• ISO/CIE 10526, ISO/CIE 10527, CIE 13.3 (colorimetric and illuminant references)
• ISO 15099 (detailed procedures for complex or scattering multiple glazing)

Keywords: ISO 9050:2003, glass in building, light transmittance, solar transmittance, total solar energy transmittance, UV transmittance, glazing factors, spectral transmittance, glazing calculations.