Determination of Light Transmittance and Haze of Packaging Materials: Principles, Methods, and Stand

Light transmittance and haze are two of the most important optical quality indicators for transparent and translucent packaging materials, directly affecting product visibility, shelf appeal, and light-protection performance. This article explains the definitions, testing principles, applicable standards such as ASTM D1003, ISO 14782, ISO 13468, and GB/T 2410, specimen requirements, and typical applications of transmittance and haze determination for packaging films, sheets, and containers.

Technical Overview

Optical performance is a decisive quality attribute for transparent and translucent packaging. Two parameters are most commonly evaluated: total luminous transmittance and haze. Total luminous transmittance (Tt) is defined as the ratio of the luminous flux transmitted through a specimen to the incident luminous flux, expressed as a percentage. Haze (H) is defined as the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam (wide-angle scattering), which is responsible for the milky or cloudy appearance of a material.

For packaging manufacturers and brand owners, these two parameters serve different purposes. Transmittance determines how much light reaches the packaged product, which is critical for light-sensitive goods, product presentation, and, in the case of agricultural films, photosynthetic efficiency. Haze determines how clearly the packaged product can be seen through the material, which directly influences consumer perception at the point of sale.

The optical behavior of a packaging material is governed by multiple factors, including:

• Polymer type and degree of crystallinity (e.g., amorphous PET versus crystalline PP)
• Material thickness and density
• Type and loading of additives such as slip agents, antiblock particles, and colorants
• Surface texture, embossing patterns, and matte or gloss finishing layers
• Processing conditions such as orientation, quenching rate, and heat-sealing
• Number and structure of layers in laminated or coextruded films

Accurate and standardized measurement of transmittance and haze allows producers to control these variables, verify compliance with product specifications, and support regulatory or customer documentation through accredited third-party laboratories.

Testing Samples

Flexible Films and Laminates

Single-layer and multilayer flexible films such as BOPP, CPP, PE, PET, PLA, and cellophane-based laminates used for flow wraps, pouches, overwrap, and window films are the most frequently tested sample category. Because film optical properties are thickness-dependent, the nominal thickness must always be reported together with the test result.

Rigid Sheets and Thermoforming Sheets

Rigid transparent sheets made of APET, RPET, PVC, PS, PP, and PLA used for thermoformed trays, clamshells, and blister packs are tested in flat sheet form. Formed containers should ideally be evaluated on flat reference plaques taken from the same production lot, since curvature makes direct measurement unreliable.

Blister and Barrier Films

Pharmaceutical blister base films (PVC, PVDC-coated PVC, PA/PVC, COC-based) and calendar blister foils are tested for transmittance both for aesthetic reasons and to assess the light exposure of photosensitive drug products.

Specimen Preparation and Conditioning

Specimens are typically cut as 50 mm × 50 mm squares or circular discs of at least 50 mm diameter so that they fully cover the illumination port of the instrument. The following precautions apply:

• Condition specimens at 23 ± 2 °C and 50 ± 10% relative humidity for a minimum of 40 hours in accordance with ISO 291 or ASTM D618, unless otherwise specified.
• Specimen surfaces must be free of fingerprints, scratches, creases, wrinkles, dust, and processing residue; clean only with a lint-free dry cloth if necessary.
• A minimum of three specimens per sample is recommended, and the mean value is reported.
• For materials with directional properties, report whether the specimen orientation affected the result.

Testing Items

The core measurement package for optical characterization of packaging materials includes:

• Total luminous transmittance (Tt): the overall percentage of incident light passing through the specimen, weighted by the CIE photopic response of the human eye.
• Diffuse transmittance (Td): the portion of transmitted light scattered beyond the 2.5-degree regular-beam limit.
• Haze (H): calculated as the ratio of diffuse transmittance to total transmittance, expressed as a percentage.
• Optional related items: narrow-angle clarity (see-through distinctness), color coordinates, and yellowness index, which can complement transmittance and haze data for full optical qualification.

Typical reference values for common materials include total transmittance of 88–92% and haze below 2% for optical-grade PET film, haze below 5% for high-clarity BOPP packaging film, and transmittance above 90% for high-quality greenhouse films.

Testing Methods

Hazemeter Method (ASTM D1003 Method A)

The most widely used procedure is Method A of ASTM D1003, performed with a dedicated hazemeter consisting of a collimated light source, an integrating sphere, and a photodetector. The measurement sequence uses four readings:

• T1: incident light reference, no specimen, with the reflectance standard in place
• T2: total light transmitted with the specimen mounted, reflectance standard in place
• T3: scattered light with the specimen mounted, light trap in position
• T4: instrument stray light with no specimen, light trap in position

From these readings, total luminous transmittance is calculated as Tt = T2 / T1 × 100%, and haze is calculated as H = (T3 − T4) / T2 × 100%. Illumination is standardized using CIE illuminant C or D65 with the appropriate standard observer, depending on the instrument configuration and the governing standard.

Spectrophotometer Method (ASTM D1003 Method B)

Method B uses a UV-Visible spectrophotometer equipped with an integrating sphere to measure total and diffuse transmittance spectrally before calculating photometric values. This approach is preferred for tinted, colored, or spectrally selective materials, since the full spectral data reveal wavelength-dependent transmission that a broadband hazemeter cannot resolve.

International and National Reference Standards

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
• ISO 13468-1 / ISO 13468-2: Plastics — Determination of the total luminous transmittance of transparent materials (single-beam and double-beam methods)
• ISO 14782: Plastics — Determination of haze for transparent materials
• GB/T 2410: Chinese national standard for the determination of luminous transmittance and haze of transparent plastics, technically aligned with the ISO approach
• JIS K 7361-1 and JIS K 7136: Japanese standards corresponding to ISO 13468-1 and ISO 14782 respectively

Instrument Calibration and Quality Control

Instruments must be zeroed and calibrated before each measurement session using certified reference standards traceable to national metrology institutes. Regular verification with calibrated transmittance and haze reference tiles, control of ambient temperature, and avoidance of port leakage are essential for achieving the repeatability and reproducibility levels stated in the standards.

Applications

Transmittance and haze determination supports a wide range of practical applications across the packaging value chain:

• Food and beverage packaging: verifying the clarity of windows in cartons, thermoformed trays, and flexible pouches so that products are clearly visible to consumers.
• Pharmaceutical packaging: assessing the light-transmission behavior of blister films and bottles to support photostability evaluation of light-sensitive drug products.
• Agricultural films: qualifying greenhouse and mulch films, where high photosynthetically active radiation (PAR) transmission directly affects crop yield and growing conditions.
• Optical and display packaging: confirming that protective films and cover sheets meet tight haze limits required for electronic displays and optical devices.
• Incoming material inspection and process control: monitoring the effect of resin changes, antiblock loading, line speed, and quenching on film optics during production.
• Recycled content qualification: demonstrating that RPET and other recyclate-based sheets and bottles achieve acceptable optical quality for direct food-contact and premium applications.
• Regulatory and customer documentation: providing standardized test reports from accredited third-party laboratories for compliance files and supplier approvals.

FAQ

What is the difference between haze and clarity?

Haze quantifies wide-angle light scattering above 2.5 degrees, which produces a milky, cloudy appearance and reduces contrast. Clarity refers to narrow-angle scattering, which affects the sharpness and distortion of images seen through the material. ASTM D1003 measures haze and transmittance, not clarity, so a material can have low haze yet still show poor image definition in certain viewing conditions.

Which standard should I choose for my product?

The choice depends on the target market and the customer specification. ASTM D1003 is widely used in North America and globally, ISO 14782 and ISO 13468 are common in international trade, GB/T 2410 applies to the Chinese market, and JIS K 7361-1 / JIS K 7136 apply in Japan. The methods are technically convergent, but results between different standards should only be compared after confirming the illuminant, observer, and geometry are equivalent.

How does specimen thickness affect the results?

Both transmittance and haze are thickness-dependent. Increased thickness generally lowers total transmittance and raises haze because more scattering interfaces and bulk material are present in the light path. For this reason, results are only comparable between specimens of the same nominal thickness, and thickness must always be stated in the test report.

Can colored, printed, or translucent materials be tested?

Yes. Tinted and colored materials are best measured with the spectrophotometer method, which captures the full spectral transmission curve. For heavily translucent or very low-transmittance materials, haze values become less meaningful because the proportion of diffuse light is inherently very high; in such cases, total transmittance and color data are usually more informative.

Is there a universal pass/fail criterion?

No single criterion exists. Acceptance limits are defined by product specifications, industry practices, or customer agreements. As general guidance, premium display and window films typically require haze below 1–2%, high-clarity food packaging films below 3–5%, and general-purpose packaging materials below 10%, while total transmittance requirements depend on whether product visibility or light protection is the priority.