ISO 13468-1:2019

Overview

ISO 13468-1:2019 specifies a practical, single-beam photometric method to determine the total luminous transmittance of planar, transparent and substantially colourless plastics in the visible region. The standard describes the required apparatus (stabilized light source, integrating sphere, photodetector), measurement procedure and reporting rules for films, sheets and mouldings (normally up to 10 mm thick). It is intended for both analytical testing and routine quality control of transparent plastics and provides a quick, precise measurement alternative to double-beam spectrophotometry.

Key topics and technical requirements

• Scope & limitations
  • Applicable to transparent, substantially colourless plastics (including faintly tinted); not for materials containing fluorescent substances.
  • Typical specimen thickness ≤ 10 mm (can be measured if instrument permits, but comparability may be affected).
• Apparatus
  • Single-beam photometer with a stabilized light source, collimating optics, integrating sphere with entrance/compensation/photodetector ports, light trap and baffles.
  • Combined light source and detector output must match the CIE standard colorimetric observer and CIE standard illuminant D (see ISO 11664-1/2).
  • Photodetector response proportional to incident flux within 1% over the working range.
  • Beam angular spread ≤ 0.087 rad (5°); beam diameter 0.5–0.8× entrance port diameter.
• Integrating sphere requirements
  • Internal reflectance ≥ 90% (±3%); total port area ≤ 3.0% of sphere internal area.
  • Compensation port used to reduce sphere inefficiency; light trap must absorb ≥ 95% of incident light.
• Procedure & measurements
  • Condition specimens per ISO 291 (23 °C ± 2 °C, 50% ± 5% RH) until thermal equilibrium.
  • Take two principal readings (incident flux and total transmitted flux with specimen) and compute percent transmittance τt = (τ2 / τ1) × 100.
  • Use three specimens (measure thickness at three points: 0.02 mm accuracy for sheet, 1 µm for film).
• Performance and precision
  • Repeatability standard deviation ≤ 0.2%; within-laboratory reproducibility not more than ~3× repeatability. Interlaboratory data show reliable results for common plastics (PMMA, PC, PS, PVC, PE, PP).

Applications and users

• Typical users: materials testing laboratories, plastic manufacturers, product quality/control engineers, R&D teams, and suppliers specifying optical performance.
• Common applications: specification of optical clarity, incoming quality control of films/sheets, verification of light transmission for glazing, displays, packaging and medical devices where transmissivity matters.

Related standards

• ISO 13468-2 - double-beam spectrophotometer method for total luminous transmittance.
• ISO 11664-1 / ISO 11664-2 (colorimetry: CIE observers and illuminants).
• ISO 291 - specimen conditioning for plastics.
• ISO 5725 series - accuracy, repeatability and reproducibility of measurement methods.

Keywords: ISO 13468-1, total luminous transmittance, transparent plastics, single-beam photometer, integrating sphere, CIE illuminant D, quality control, optical transmittance measurement.