Light transmission performance evaluation of packaging materials is a critical quality control process that measures total luminous transmittance, haze, and spectral blocking properties of films, sheets, and rigid containers. This technical article explains the key optical parameters, internationally recognized test standards such as ASTM D1003 and ISO 13468-1, sample preparation requirements, and practical applications across the food, pharmaceutical, and cosmetics packaging industries.
Technical Overview
Light transmission performance refers to the ability of a packaging material to transmit, scatter, or block incident light across the visible and ultraviolet regions of the electromagnetic spectrum. For transparent and translucent packaging materials such as plastic films, rigid sheets, bottles, and blister foils, optical performance directly affects both product protection and consumer perception. Excessive light exposure can trigger photodegradation reactions in packaged goods, including vitamin loss in beverages, lipid oxidation in edible oils, color fading in cosmetics, and potency degradation in pharmaceuticals.
The evaluation of light transmission performance is typically quantified through three primary optical parameters: total luminous transmittance, haze, and clarity. Total luminous transmittance (TLT) measures the percentage of incident light that passes through the specimen, haze quantifies the percentage of transmitted light that is scattered by more than 2.5 degrees from the incident beam, and clarity describes the ability to distinguish fine detail through the material. Accredited third-party laboratories and in-house quality control departments rely on standardized test methods published by ISO, ASTM, and GB to ensure reproducible, comparable results across global supply chains.
Testing Samples
Flexible Plastic Films
Flexible films represent the largest sample category for light transmission evaluation, including mono-layer and multilayer structures of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and biodegradable polymers such as PLA. Film specimens are typically conditioned at 23 ± 2 °C and 50 ± 10% relative humidity prior to testing, and multiple thickness points are measured to account for gauge variation across the web.
Rigid Sheets and Thermoformed Containers
Rigid sheets used for thermoformed trays, clamshells, and blister packs require transmittance evaluation because wall thickness and draw-down ratios during thermoforming can significantly alter optical properties. Specimens are cut from flat regions of formed containers whenever possible, or from the parent sheet stock for material qualification purposes.
Bottles, Vials, and Hollow Containers
For hollow containers, sections are cut from the sidewall, shoulder, and base to characterize positional variation in wall thickness. Pharmacopoeial light protection studies for pharmaceutical containers frequently require transmittance profiling across the full wavelength range from 290 nm to 450 nm.
Coated, Metallized, and Composite Materials
Light-blocking structures such as aluminum-metallized films, UV-coated laminates, and paper-plastic composites are evaluated to verify barrier performance. These samples are tested for residual transmittance at wavelengths relevant to product sensitivity, particularly in the ultraviolet region.
Testing Items
A comprehensive light transmission performance evaluation typically encompasses the following measurable parameters:
- Total luminous transmittance (TLT), expressed as the percentage of incident visible light (typically illuminant D65 with the standard photopic observer function) that passes through the specimen
- Haze, expressed as the percentage of transmitted light deviating from the incident beam by more than 2.5 degrees due to forward scattering
- Clarity or see-through quality, describing the resolution of fine objects viewed through the material at short distances
- Ultraviolet transmittance, measured separately in the UV-A (315–400 nm) and UV-B (280–315 nm) regions to verify light protection performance
- Spectral transmittance distribution, providing a full wavelength scan from approximately 200 nm to 800 nm for photosensitivity analysis
- Color coordinates of transmitted light, including CIE L*a*b* values, to assess color neutrality of transparent packaging
Testing Methods
Light transmission testing is performed using integrating sphere spectrophotometers and dedicated hazemeters operated according to internationally recognized standards. The most widely applied methods include:
- ASTM D1003 — Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, the dominant method in North America for simultaneous haze and transmittance measurement using Method A (hazemeter) or Method B (spectrophotometer)
- ISO 13468-1 — Plastics: Determination of the total luminous transmittance of transparent materials using a single-beam integrating sphere instrument
- ISO 14782 — Plastics: Determination of haze for transparent materials, specifying the reference geometry for scattered light measurement
- GB/T 2410 — the Chinese national standard for determination of light transmittance and haze of transparent plastics, technically aligned with the international methods above
- ASTM D1746 — Standard Test Method for Transparency of Plastic Sheeting, applied where regular transmittance of high-clarity films must be measured at a defined geometry
- JIS K 7361-1 and JIS K 7136 — Japanese industrial standards corresponding to total luminous transmittance and haze determination respectively
- Pharmacopoeial light-transmission testing for pharmaceutical containers, which verifies that container wall transmittance remains below defined limits across the 290–450 nm phototoxicity window
During test execution, specimens are mounted perpendicular to the incident beam, unscattered and scattered transmitted light components are collected by the integrating sphere, and calibration is verified using reference standards traceable to national metrology institutes. A minimum of three to five specimens per sample is typically measured, and results are reported as mean values with standard deviations.
Applications
Light transmission performance data supports critical decisions across multiple packaging sectors:
- Food and beverage packaging: verification of UV barrier performance in milk bottles, edible oil containers, beer bottles, and juice cartons to prevent nutrient degradation, rancidity, and flavor loss
- Pharmaceutical packaging: qualification of blister foils, tablets bottles, and ampoules against light protection requirements for photosensitive active ingredients
- Cosmetics packaging: control of haze and clarity in cosmetic bottles, jars, and closures where visual appeal is a decisive consumer factor
- Agricultural films: tuning of light-diffusing greenhouse films to optimize photosynthetically active radiation (PAR) delivery while scattering direct sunlight
- Electronics and display protection: qualification of optical-grade films where high transmittance above 90% combined with haze below 1% is frequently specified
- Material development and supplier qualification: benchmarking of new polymer formulations, coatings, and recycled content against established optical specifications
FAQ
What is the difference between transmittance and haze?
Transmittance measures the total quantity of light passing through a material, while haze measures the portion of that transmitted light that is diffusely scattered. A material can exhibit high transmittance together with high haze, meaning it lets light through but obscures the view of objects behind it.
What transmittance values are considered acceptable for transparent packaging?
Acceptance limits depend entirely on the application. General-purpose transparent films commonly exceed 88–92% total luminous transmittance with haze below 2%, whereas light-blocking pharmaceutical or beer packaging may intentionally require transmittance below 10% in the UV region. Specification limits should always be agreed between brand owner and supplier.
How should specimens be prepared before testing?
Specimens must be clean, free of fingerprints, scratches, and surface contamination, and large enough to fully cover the instrument aperture. Conditioning at standard laboratory atmosphere of 23 ± 2 °C and 50 ± 10% relative humidity is recommended, and thickness should be reported because transmittance decreases predictably with increasing thickness.
Which standard should be selected: ASTM D1003 or ISO 13468-1?
Both methods measure total luminous transmittance with closely comparable results for most materials. The choice is usually dictated by the regulatory market of the end product or by contractual agreement, with ASTM D1003 favored in North America and ISO methods preferred in Europe, Asia, and internationally harmonized supply chains.
Can colored or opaque packaging be tested?
Yes. While total luminous transmittance of opaque materials approaches zero, spectral scanning remains valuable to quantify residual UV leakage and to verify the effectiveness of pigments, coatings, and metallized barrier layers used for light-sensitive products.