Determination of Light Transmittance Parameters of Packaging Materials

Light transmittance testing of packaging materials measures the percentage of incident light that passes through films, sheets, and rigid containers, directly affecting product visibility, shelf appeal, and protection of light-sensitive contents. This technical article explains the key transmittance parameters, applicable test methods such as ASTM D1003, ISO 13468, and GB/T 2410, and typical applications across food, pharmaceutical, and consumer packaging. Accredited third-party laboratories rely on these standardized procedures to deliver reproducible and comparable optical performance data.

Technical Overview

Light transmittance, also known as luminous transmittance (Tt), is defined as the ratio of luminous flux transmitted through a specimen to the luminous flux incident upon it, expressed as a percentage under standardized illumination conditions (typically CIE Standard Illuminant D65 or Illuminant A with photopic vision). For transparent packaging, this parameter determines how clearly consumers can see the packaged product and how effectively the material shields light-sensitive contents from photodegradation.

Haze (H), the companion parameter to transmittance, quantifies the percentage of transmitted light that deviates from the incident beam direction by more than 2.5 degrees due to wide-angle scattering. High haze values produce a milky, cloudy appearance that reduces product visibility even when total transmittance remains high. Together, transmittance and haze provide a complete optical profile of transparent and translucent packaging materials, supporting decisions in material selection, formulation optimization, and incoming quality control.

Testing Samples

Flexible Plastic Films

Single-layer and multilayer flexible films are the most frequently tested sample category, including BOPP, CPP, LDPE, LLDPE, PET, PA, and PVC films used for pouches, overwraps, bags, and laminates. Typical specimen thickness ranges from 15 to 100 micrometers. Specimens must be free of wrinkles, creases, fingerprints, and surface contamination, as these defects artificially increase measured haze.

Rigid Sheets and Thermoformed Containers

Transparent and translucent rigid materials such as APET, RPET, PVC, PS, PP, PC, and PMMA sheets are tested for blister packs, clamshells, trays, and transparent boxes. Flat sheet sections with thicknesses between 0.2 and 2 millimeters are the preferred specimen form, while curved container walls may require sectioning or the use of specially adapted fixtures.

Pharmaceutical Packaging Materials

Blister films, COP and COC containers, transparent tube sections, and lidding materials are tested to support photostability assessments conducted in accordance with ICH Q1B. Optical data help determine whether additional UV-blocking layers or secondary cartons are required to protect photosensitive drug products.

Coated, Colored, and Specialty Materials

Anti-fog films, UV-absorbing coated films, semi-transparent metallized structures, tinted or dyed materials, biodegradable PLA films, and translucent paper-based packaging can all be characterized. For heavily scattering or diffusing materials, integrating sphere measurements are essential to capture both regular and diffuse transmittance components accurately.

Testing Items

The core optical parameters determined for packaging materials include:

• Total luminous transmittance (Tt), the overall percentage of visible light passing through the specimen.
• Parallel (regular) transmittance (Tp), the percentage of light transmitted without scattering.
• Diffuse transmittance (Td), the scattered component of transmitted light.
• Haze (H), the wide-angle scattering ratio calculated from Td and Tt.
• Ultraviolet transmittance and UV blocking ratio across UVA (315 to 400 nm) and UVB (280 to 315 nm) bands.
• Transmittance uniformity, evaluated by testing multiple positions across a material web or sheet.

Testing Methods

Hazemeter Method (ASTM D1003 Method A)

A calibrated hazemeter based on an integrating sphere optics system illuminates the specimen with a parallel light beam. The unscattered beam is trapped or measured first, followed by total transmitted light measurement, allowing direct calculation of both total transmittance and haze. This method offers rapid measurement suitable for high-volume quality control and is widely specified in packaging specifications.

Spectrophotometer Method (ASTM D1003 Method B and ISO 13468-2)

A UV-visible spectrophotometer equipped with an integrating sphere collects a full spectral transmittance scan, typically from 200 to 780 nanometers. Photopic transmittance is computed by weighting the spectral data with the CIE photopic luminosity function. The spectrophotometric approach additionally provides ultraviolet transmittance data required for evaluating UV protection performance.

International and National Standards

ISO 13468-1 and ISO 13468-2 specify the determination of total luminous transmittance using integrating sphere techniques, while ISO 14782 covers haze determination for transparent plastics. GB/T 2410 defines the corresponding Chinese national method and is technically harmonized with ASTM D1003. Accredited third-party laboratories select the appropriate standard based on customer requirements, product specifications, and target markets.

Specimen Preparation and Conditioning

Specimens are conditioned in a standard laboratory atmosphere, typically 23 degrees Celsius and 50 percent relative humidity in accordance with ISO 291, for a minimum of 40 hours before measurement. A minimum of three to five specimens are tested at different positions, and results are reported as individual values and arithmetic means. Specimen geometry, thickness measurement, and surface handling are documented to ensure traceability and repeatability.

Applications

Transmittance data support a broad range of packaging development and quality assurance activities:

• Food and beverage packaging, where light-induced oxidation affects dairy products, edible oils, beer, and processed foods, and where high clarity drives shelf appeal for transparent pouches and bottles.
• Pharmaceutical packaging, where optical performance is integrated with photostability studies to protect light-sensitive active ingredients.
• Cosmetics and personal care packaging, where UV filtering and color fidelity of transparent containers influence both product protection and premium presentation.
• Electronics and display packaging, where anti-glare and low-haze window films protect screens while maintaining visibility.
• Material research and incoming inspection, comparing resin formulations, masterbatch loadings, coating processes, and recycling impacts on RPET optical quality.

FAQ

What is the difference between transmittance and haze?

Transmittance measures the total quantity of light passing through a material, while haze measures the fraction of that transmitted light scattered at angles greater than 2.5 degrees. A material can exhibit high transmittance yet high haze, appearing bright but not transparent, which is why both parameters should be reported together.

Which test standard should be selected?

ASTM D1003 and GB/T 2410 are the most common choices for North American and Chinese markets respectively, while ISO 13468 and ISO 14782 are preferred for international specifications. The methods are technically aligned, so selection typically depends on the regulatory context and the requirements stated in purchase agreements.

What specimen size and condition are required?

Standard hazemeters typically require flat specimens of approximately 50 by 50 millimeters, while spectrophotometer accessories accept smaller apertures. Specimens must be flat, clean, and representative of production material, and they must be conditioned at standard temperature and humidity before testing.

Can printed, tinted, or metallized packaging be tested?

Yes. Printed and tinted materials are measured at unprinted regions or full-surface as specified by the client, and semi-transparent metallized films are characterized using integrating sphere optics. Results for such materials should clearly identify the measured area and illumination geometry.

How does material thickness affect the results?

Increased thickness generally reduces total transmittance and may increase haze due to bulk scattering. Because transmittance is thickness-dependent, comparisons between materials are only valid when thickness values are similar or when results are normalized and reported together with measured thickness.

What is the typical testing turnaround time?

For routine transmittance and haze measurements on conditioned flat specimens, accredited third-party laboratories generally complete testing within three to five working days, with expedited services available for urgent quality control investigations.