Overview
ISO 26723:2020 - Plastics - Determination of total luminous transmittance and reflectance - defines a laboratory method to measure total luminous transmittance and total luminous reflectance of clear, translucent and opaque plastics (films, sheets, moulded plaques/discs). The standard extends measurement capability beyond planar, colourless plastics (covered by ISO 13468‑1) by providing a method to trap and measure diffused edge-scattered light, making it suitable for highly scattering (translucent) and opaque materials. Fluorescent and strongly chromatic-colour plastics are excluded.
Key topics and technical requirements
- Measurement principle: use of an integrating sphere and optical system to collect transmitted and reflected luminous flux, including light scattered to specimen edges.
- Apparatus essentials:
- Stabilized light source and photometer with filter corresponding to the photopic luminous-efficiency function V(λ) (CIE standard observer).
- Integrating sphere geometry and port arrangement (total port area ≤ 4.0% of internal sphere area; recommended sphere diameter ≥ 150 mm).
- Light trap, white reference (e.g., barium sulfate or PTFE), specimen holder with metallic inner surface when needed.
- Specimen requirements:
- Flat specimens machined from films, sheets or moulded articles; original thickness retained.
- Two handling modes: without specimen holder (for thin/low-haze samples) and with specimen holder (for thicker/high-haze samples where edge-loss is significant).
- Conditioning in standard atmosphere per ISO 291 (typically 23 °C ±2 °C and 50 % RH ±10 %).
- Procedure and calculations:
- Defined measurement sequence (reference, transmission, trap, reflection) with instrument readings τ1…τ4.
- The standard provides formulae to compute total luminous transmittance (%) and total luminous reflectance (%) from measured signals.
- Reporting and precision:
- Results expressed to one decimal place; minimum reporting items listed (equipment, specimen description, evaluation type, average of three specimens, etc.).
- Interlaboratory precision data were not available at publication; examples and derivations are provided in annexes.
Applications
- Optical performance testing of lighting diffusers, backlit panels, opal sheets, and other scattering plastics.
- Quality control and specification verification in plastics manufacturing and extrusion/coating lines.
- Material selection for architectural glazing, signage, and luminaires where balance of transmission and reflectance affects appearance and efficiency.
- R&D and product development when evaluating translucency, haze effects, or combined transmission/reflectance behavior.
Who should use ISO 26723:2020
- Test laboratories and QA/QC teams in plastics, lighting and building-material industries
- Polymer scientists and optical property specialists
- Product designers and specifiers in lighting, displays and architectural applications
- Standards writers and compliance assessors requiring a standardized method for diffuse/translucent materials
Related standards
- ISO 13468‑1 (planar transparent, substantially colourless plastics)
- ISO/CIE 11664‑1 and ISO 11664‑2 (colorimetry - CIE observers and standard illuminants)
- ISO 291 (conditioning of specimens)
Keywords: ISO 26723:2020, total luminous transmittance, total luminous reflectance, plastics testing, integrating sphere, diffuse transmission, haze, specimen conditioning, V(λ).