Light Transmittance Testing of Packaging Materials: Industry Standard Methods and Applications

Light transmittance testing measures the percentage of visible light that passes through transparent and translucent packaging materials such as films, sheets, bottles, and blister foils, and it is a critical quality control step for product visibility, light protection, and regulatory compliance. Industry standards such as ASTM D1003, ISO 13468, GB/T 2410, and pharmaceutical industry specifications define the instruments, procedures, and acceptance criteria used for this testing. This article explains the technical principles, sample requirements, test methods, and typical applications of industry standard light transmittance testing for packaging materials.

Technical Overview

Light transmittance (luminous transmittance) is defined as the ratio of luminous flux transmitted through a specimen to the luminous flux incident upon it, expressed as a percentage. The measurement is evaluated under a specified CIE standard illuminant (typically Illuminant A or D65) and the CIE photopic observer function, which weights the spectral range of approximately 380 nm to 780 nm according to human visual sensitivity. A closely related parameter, haze, expresses the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam, causing a loss of clarity.

For packaging materials, transmittance testing serves two opposing engineering objectives. On one hand, high transparency is desirable for retail display, allowing consumers to inspect the product. On the other hand, many products require light protection: pharmaceuticals can undergo photodegradation under exposure to ultraviolet and visible light, foodstuffs containing fats, oils, or vitamins are susceptible to light-induced oxidation, and cosmetic actives may lose potency. Industry standard transmittance testing allows manufacturers to demonstrate, with traceable and reproducible data, that a packaging material achieves the correct balance between clarity and light shielding.

The testing framework combines national standards such as GB/T 2410 (determination of light transmittance and haze of transparent plastics in China), international standards including ASTM D1003, ISO 13468, ISO 14782, JIS K 7361-1, and JIS K 7136, and sector-specific industry standards. Notable among these are the YBB standards governing pharmaceutical packaging materials and containers, which specify transmittance requirements for glass and plastic containers, as well as YY/T standards for medical device packaging and BB/T standards for general packaging applications. Accredited third-party laboratories routinely perform these tests for regulatory submission, supplier qualification, and incoming inspection.

Testing Samples

Flexible Plastic Films and Sheets

Single-layer and multilayer films of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), polyvinyl chloride (PVC), and cyclic olefin materials constitute the largest sample category. Specimens are typically cut to squares of approximately 50 mm × 50 mm, free of creases, wrinkles, bubbles, and surface contamination, and are usually tested at a nominal thickness of less than 3 mm in accordance with ASTM D1003.

Rigid Transparent Containers and Sheets

Sections cut from PET bottles, PP jars, PVC or PVDC blister bases, acrylic and polycarbonate sheets, and thermoformed trays are tested after being flattened or prepared as flat coupons. When the container geometry does not permit a flat specimen, sections are taken from the wall at specified locations so that the measurement reflects the actual material as produced.

Pharmaceutical Packaging Materials

Glass vials, ampoules, infusion bottles, oral liquid bottles, infusion bags, and pharmaceutical-grade plastic containers are tested in accordance with the relevant YBB transmittance method. Clear glass and plastic containers must often demonstrate high transmittance in the visible region, whereas amber and other light-protective colored containers must demonstrate defined transmittance limits across specified wavelength bands to prove their photoprotective function.

Composite Laminates, Coated and Metallized Materials

Barrier laminates, UV-absorbing coated films, tinted materials, and metallized structures are tested to verify that light-blocking layers perform as designed. Even nominally opaque packaging is often subjected to transmittance measurement, because a small residual transmittance in the ultraviolet region can be significant for highly photosensitive contents.

Testing Items

Industry standard transmittance testing for packaging materials typically covers the following parameters:

• Total luminous transmittance (Tt): the overall percentage of incident visible light that passes through the specimen, including both directly transmitted and scattered components.
• Haze (turbidity): the percentage of transmitted light deviating more than 2.5 degrees from the incident direction, quantifying loss of clarity and see-through quality.
• Regular (specular) transmittance: the undeviated component of transmitted light, which determines image clarity through the material.
• Diffuse transmittance: the scattered component, calculated as the difference between total and regular transmittance.
• Spectral transmittance: wavelength-specific transmittance data across the ultraviolet range (200 nm to 380 nm) and visible range (380 nm to 780 nm), used to evaluate UV-blocking performance and photoprotective behavior.
• Light-shielding ratio: the complement of transmittance, commonly reported for opaque or metallized protective packaging.

Acceptance criteria depend on the product and the applicable industry standard. For example, pharmacopoeial and YBB-style requirements specify maximum transmittance values at defined wavelengths for light-protective pharmaceutical containers, while high-clarity films for display packaging are frequently qualified against minimum transmittance and maximum haze limits agreed with the brand owner.

Testing Methods

Hazemeter Method (ASTM D1003 Method A, GB/T 2410 Method A)

The hazemeter employs a light source, a photodetector, and an integrating sphere with a defined aperture. Four readings are taken: T1 (incident light), T2 (total light transmitted by the specimen), T3 (light scattered by the instrument alone), and T4 (light scattered by both instrument and specimen). Total luminous transmittance is calculated as Tt = (T2 / T1) × 100%, and haze is calculated as Haze = [(T4 − T3) / T2] × 100%. This method is fast, highly reproducible, and well suited to routine quality control of films and sheets.

Spectrophotometer Method (ASTM D1003 Method B, ISO 13468, JIS K 7361-1)

An integrating-sphere spectrophotometer scans the specimen across the visible spectrum and mathematically weights the measured spectral transmittance with the CIE photopic observer function and the selected standard illuminant. This method provides full spectral information, enabling separate evaluation of ultraviolet, visible, and wavelength-band transmittance. It is preferred when photoprotective performance at specific wavelengths must be demonstrated, such as for amber pharmaceutical glass or UV-absorbing coated films.

Industry Standard Method for Pharmaceutical Packaging (YBB Transmittance Determination)

Specimens are prepared from the body or wall of the container, conditioned, and measured at the wavelength or wavelength bands specified by the applicable material standard. For clear containers, minimum transmittance thresholds confirm optical quality; for colored light-protective containers, maximum transmittance limits across the biologically relevant wavelength range confirm adequate shielding, complementing photostability studies conducted under ICH Q1B principles.

Sample Preparation and Conditioning

Specimens must be clean, flat, and representative of production material. Unless otherwise specified, samples are conditioned in a standard laboratory atmosphere of 23 °C ± 2 °C and 50% ± 5% relative humidity before measurement. Surface defects, fingerprints, scratches, and embedded particles must be excluded, as they artificially increase haze. Multiple specimens (commonly five or more) are tested and averaged to characterize material variability.

Instrument Calibration and Quality Control

Instruments are zeroed and span-calibrated before each session, and calibration is verified using reference standards traceable to national metrology institutes. Periodic verification with certified transmittance standards, control charts, and participation in interlaboratory comparisons ensure that results from accredited third-party laboratories remain accurate and comparable between sites and over time.

Applications

Pharmaceutical and Medical Packaging

Transmittance data support the selection and qualification of packaging for photosensitive drug products, verification of light-protective amber glass and colored plastics, and regulatory documentation demonstrating that the packaging system contributes to maintaining product quality throughout shelf life.

Food and Beverage Packaging

Films, bottles, and lids are screened for transmittance to limit light-induced oxidation of oils, vitamins, and pigments, to extend shelf life, and to balance product visibility at the point of sale with adequate protection during storage under retail lighting.

Cosmetic and Personal Care Packaging

Transparent and tinted containers for skincare actives, essential oils, and fragrance products are tested to ensure that formulations remain stable and visually appealing while the consumer can still evaluate the product.

Industrial, Electronic, and Specialty Films

Protective films for displays, optical laminations, window films, agricultural packaging, and biodegradable or nanocomposite films under development rely on standardized transmittance and haze measurements to benchmark optical performance and confirm formulation changes.

FAQ

What is the difference between light transmittance and haze?

Light transmittance measures how much visible light passes through the material, while haze measures how much of that transmitted light is scattered away from the straight-through direction. A material can have high transmittance yet high haze: it lets plenty of light through but produces a cloudy, unclear view. Both parameters are needed to fully characterize optical quality.

Which standard should be selected for a given packaging material?

For general plastic films and sheets, ASTM D1003 or GB/T 2410 is the common choice, with ISO 13468 and JIS K 7361-1 used for international harmonization. Pharmaceutical packaging in regulated markets is tested under the applicable YBB or pharmacopoeial transmittance requirements, while medical device packaging may reference YY/T series standards. The governing standard should always follow the end-use regulation and the customer specification.

What sample size and quantity are required?

Most methods require flat specimens larger than the instrument aperture, typically squares of at least 50 mm × 50 mm, with thickness within the range allowed by the standard. For containers, flat sections are cut from the container wall. Testing at least three to five specimens per sample is recommended to account for material variability.

Can translucent, tinted, or embossed materials be tested?

Yes. Tinted and translucent materials are measured for total and spectral transmittance, and results are interpreted against the wavelength-specific limits of the applicable standard. Heavily embossed or textured specimens may show elevated diffuse components, and this is usually reported explicitly as diffuse or wide-angle transmittance rather than regular transmittance.

How do transmittance results relate to light protection and shelf life?

Lower transmittance across the ultraviolet and short-wavelength visible regions generally means greater protection against photodegradation. Transmittance data are combined with photostability testing of the actual product to demonstrate that the packaging system, together with any secondary packaging, keeps the product within specification throughout its intended shelf life.