Light Transmittance Testing Standards for Packaging Materials: Methods, Parameters and Applications | ZHONGXI Testing Greece,Global Testing and Certification Institute.

Light transmittance is a critical optical property that determines how packaging materials protect, preserve, and present products across the food, pharmaceutical, and consumer goods industries. This technical article explains the international and national testing standards for packaging material light transmittance, covering sample types, measurable parameters, instrument methods, and practical applications. Whether you are qualifying food-grade films or validating light-resistant pharmaceutical packaging, understanding these standards ensures accurate, comparable, and compliant test results.

Technical Overview

Light transmittance testing measures the fraction of incident light that passes through a packaging material, typically expressed as a percentage over the visible spectrum (380–780 nm) or specific wavelength bands such as ultraviolet (UV) regions. For transparent and translucent packaging—films, sheets, bottles, and blister foils—transmittance directly influences product shelf life, visual presentation, and regulatory compliance. Light-sensitive products such as vitamins, pharmaceuticals, fats, beverages, and pigmented foods can degrade photochemically when exposed to UV or visible radiation, making quantified optical performance a core requirement in packaging specification sheets.

Several internationally recognized standards govern transmittance measurement, and each defines the optical geometry, light source, detector response, and calculation method. Selecting the correct standard depends on the material form (film versus rigid container), the regulatory market, and whether total transmittance alone or haze (wide-angle scattering) must also be reported. Most specifications require testing by accredited third-party laboratories using calibrated spectrophotometers or hazemeters equipped with integrating spheres.

ASTM D1003 – Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics (the most widely cited method for plastic films and sheets).
ISO 13468-1 / ISO 13468-2 – Determination of the total luminous transmittance of transparent plastics, using a single-beam and double-beam integrating sphere method respectively.
ISO 14782 – Determination of haze for transparent materials.
ASTM D1746 – Standard Test Method for Transparency of Plastic Sheeting using a ratio method.
GB/T 2410 – Chinese national standard for luminous transmittance and haze of transparent plastics, technically aligned with ASTM D1003.
JIS K 7361-1 – Japanese standard equivalent to ISO 13468-1 for total luminous transmittance.
GB/T 14216 and related film-specific methods for plastic film light transmittance.

These standards normalize the photometric scale to CIE standard illuminant D65 or A with a photopic (V λ) detector response, ensuring that reported values represent human visual perception rather than raw energy measurements. This harmonization allows transmittance data generated in different laboratories worldwide to be compared directly.

Testing Samples

Flexible Plastic Films

Flexible films are the largest sample category, including monolayer and multilayer structures of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and coated barrier films. Samples are typically cut into flat specimens of at least 50 mm × 50 mm, free from creases, wrinkles, surface contamination, and printing inks in the measurement area. Multi-layer laminates are tested as finished structures because each interface contributes to reflection and scattering losses.

Rigid Plastic Sheets and Containers

Rigid materials include PET and PVC sheets for thermoformed trays, blister films, and sections cut from bottles, jars, and closures. Curved container walls must be flattened or cut into flat panels where possible; where curvature cannot be removed, specialized holders or ring-support fixtures are used to keep the light path perpendicular to the surface. Sample thickness must be reported since transmittance decreases predictably with thickness.

Transparent Barrier and Functional Coatings

Materials such as transparent aluminum oxide (AlOx) and silicon oxide (SiOx) coated films, transparent metallized films, and UV-blocking coated films are tested to verify that barrier functionality has not compromised clarity. Wavelength-scan measurements across 200–800 nm are recommended for these samples to confirm UV cutoff behavior.

Sample Conditioning and Preparation

Condition specimens at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 40 hours unless otherwise specified.
Test at least three to five specimens per sample lot and report the arithmetic mean.
Avoid touching the optical measurement surfaces; clean only with methods that do not alter the surface (lint-free wipes, dry air).
Report specimen thickness at the measurement point to the nearest 0.001 mm for films or 0.01 mm for sheets.

Testing Items

Transmittance testing programs for packaging materials typically include the following measurable parameters:

Total Luminous Transmittance (T_t) – The percentage of normally incident luminous flux that passes through the specimen, including both direct and diffuse components. This is the headline figure in most packaging specifications (e.g., "≥ 90% transmittance").
Haze – The percentage of transmitted light that is scattered more than 2.5° from the normal axis. High haze creates a milky appearance, reduces product visibility, and may indicate crystallinity, gel contamination, or surface abrasion.
UV Transmittance (UVA 315–380 nm / UVB 280–315 nm) – Critical for light-protective packaging; low UV transmittance indicates effective protection of photosensitive contents such as vitamins, beer, and pharmaceuticals.
Visible Spectral Transmittance Curve – A full wavelength scan (typically 200–800 nm at 1–10 nm intervals) revealing colored tints, absorption bands, and cutoff wavelengths.
Clarity / See-Through Quality – A measure of narrow-angle scattering affecting the sharpness of images viewed through the material, relevant for retail display packaging.
Parallel / Direct Transmittance (T_p) – The unscattered component, from which haze is derived (Haze = (T_t − T_p) / T_t × 100).

Testing Methods

Spectrophotometer with Integrating Sphere (ASTM D1003, ISO 13468-2)

A double-beam spectrophotometer fitted with an integrating sphere collects both directly transmitted and diffusely scattered light, yielding total luminous transmittance. The specimen is placed at the sphere port with a matte surface facing the source for haze measurement. The instrument performs baseline correction with no specimen and with a white (opaque) reference for haze zeroing. Photometric values are integrated over the visible spectrum using the CIE photopic observer function, and the result is reported as percent transmittance and percent haze.

Hazemeter Method (ASTM D1003 Method B, ISO 14782)

A dedicated hazemeter uses a standardized light source, collimating optics, and an integrating sphere with a light trap ( or "Z" type sphere). Four successive readings—incident flux, total transmitted flux, diffuse flux with the light trap open, and instrument scattered flux—yield total transmittance and haze in a single rapid measurement. This method is favored for quality control on production lines due to its speed and simplicity.

Wavelength Scan Method (Spectral Transmittance)

For UV-protective and tinted packaging, a UV-Vis spectrophotometer scans the specimen across 200–800 nm. Key reported outputs include transmittance at specific wavelengths (e.g., 290 nm, 373 nm for pharmaceutical light protection), the 50% cutoff wavelength, and integrated UV-A and UV-B blocking percentages.

Container and Blister Testing

Finished containers may be evaluated by cutting flat panels from the sidewall, or by using accessories designed for intact bottles and vials. Pharmaceutical light protection is commonly validated against pharmacopoeial exposure categories that specify the wavelength range and required transmittance limits over defined thickness intervals.

Measurement Uncertainty and Quality Control

Instrument wavelength accuracy verified with holmium oxide or didymium filters; photometric accuracy verified with certified transmittance standards.
Zero and 100% baseline checks performed before each measurement session.
Reported results should include specimen description, thickness, conditioning, standard method used, and individual and mean values.
Inter-laboratory reproducibility for luminous transmittance is typically within ±1–2% under properly controlled conditions.

Applications

Transmittance test data directly support packaging design, regulatory submission, and supplier qualification across many sectors:

Food and Beverage Packaging – Verifying UV-barrier films for edible oils, dairy products, beer, and juices to prevent photo-oxidation, rancidity, and "light-struck" flavor defects while maintaining retail shelf clarity.
Pharmaceutical and Nutraceutical Packaging – Demonstrating compliance with light-protection requirements for photosensitive drugs, vitamins, and biologics; selecting amber glass, opaque HDPE, or UV-absorbing blister films based on measured spectral cutoff.
Agricultural and Horticultural Films – Although strictly outside retail packaging, greenhouse and mulch films rely on the same standards to balance photosynthetically active radiation (PAR) transmission with UV exclusion for pest control.
Consumer Electronics and Display Packaging – Window films, screen protectors, and clear PET cartons require high transmittance (> 90%) with low haze for premium presentation.
Cosmetics Packaging – Matching tinted or frosted containers to brand aesthetics while protecting fragrance and active ingredients from photodegradation.
Supplier Qualification and Lot Release – Incoming inspection specifications referencing ASTM D1003 or GB/T 2410 acceptance limits, supporting ISO 9001 quality management systems and customer audits.
Product Development – Comparing resin grades, thickness optimization, additive levels (UV absorbers, clarifiers), and the optical impact of coatings and metallization during material selection.

FAQ

Q1: What is the difference between transmittance and haze?

Transmittance quantifies how much light passes through the material in total, while haze quantifies how much of that transmitted light is scattered at wide angles (greater than 2.5° from the normal). A material can have 90% transmittance yet 30% haze, meaning it passes light efficiently but appears cloudy and obscures the view of the packaged product.

Q2: Which standard should I specify for a plastic film—ASTM D1003 or ISO 13468?

Both methods produce closely comparable total luminous transmittance values. ASTM D1003 is the most common reference in North American supply chains and includes haze in a single procedure. ISO 13468-2 is preferred when ISO alignment is required (often in combination with ISO 14782 for haze). When in doubt, specify the standard that matches your customer's or regulator's documentation, and note that results are generally interchangeable within normal measurement uncertainty.

Q3: Can I test a curved bottle or blister pack directly?

Wherever possible, flat panels are cut from the container wall for accurate measurement, because curvature introduces refraction and scattering artifacts. Intact-container measurements are possible with appropriate accessories but should be clearly identified as such in the report, since results may differ systematically from flat-specimen values.

Q4: Why does UV transmittance matter for food and pharma packaging?

UV radiation between 280 and 400 nm drives photochemical degradation of fats, vitamins (especially A, B2, B6, B12, C, D, and K), pigments, fragrances, and active pharmaceutical ingredients. Measuring UV transmittance verifies that the packaging delivers the intended protection, and full spectral scans identify the cutoff wavelength where blocking begins.

Q5: How thick should test specimens be, and does thickness affect results?

Specimens should be tested at their actual use thickness, because transmittance decreases roughly exponentially with thickness according to the Beer–Lambert relationship. Always report thickness alongside transmittance; comparing materials of different thicknesses without normalization can lead to incorrect conclusions.

Q6: How many specimens are required for a valid test?

Most standards recommend a minimum of three specimens per sample, with the mean value reported. For lot-release decisions or referee testing, five or more specimens from different positions across the web or container provide better statistical confidence and capture within-sample variability such as gauge variation or coating non-uniformity.