Light Transmittance Testing of Plastic Cling Film: Standards, Methods, and Applications

Light transmittance testing measures the percentage of visible light that passes through plastic cling film (food wrap), a critical optical quality parameter that affects retail display, consumer appeal, and light protection for packaged foods. This technical guide explains the testing principles, applicable international standards such as ASTM D1003, ISO 13468, and GB/T 2410, specimen preparation requirements, instrumentation, and typical applications for film manufacturers and accredited third-party laboratories.

Technical Overview

Light transmittance, also referred to as luminous transmittance, is defined as the ratio of transmitted luminous flux to incident luminous flux, expressed as a percentage, measured under specified geometric and spectral conditions covering the visible wavelength range of 380 to 780 nm. For food-grade cling film, transmittance and its companion parameter haze determine how clearly packaged food can be observed through the wrap, which is a key commercial attribute for retail presentation and consumer acceptance.

Cling film is manufactured primarily from linear low-density polyethylene (LLDPE), plasticized polyvinyl chloride (PVC), polyvinylidene chloride (PVDC)-based multilayer structures, and increasingly from bio-based resins such as PLA and PBAT blends. Because these polymers differ in crystallinity, refractive index, and additive content, well-formed thin films typically exhibit total luminous transmittance values in the range of approximately 88% to 93%.

Since cling film gauge is extremely thin, usually 8 to 15 micrometers, optical measurements are highly sensitive to wrinkles, dust, fingerprints, and gauge variation. Standardized specimen preparation, environmental conditioning, and instrument calibration are therefore essential for reproducible and comparable results between laboratories.

Testing Samples

Polyethylene (PE) Cling Film

LLDPE-based household and catering wrap, typically 8 to 12 micrometers thick. PE film offers good clarity and high transmittance, generally above 90%. Transmittance testing verifies additive dispersion, gauge uniformity, and the absence of processing defects such as gels or fish-eyes.

Polyvinyl Chloride (PVC) Cling Film

Plasticized PVC wrap is widely used for fresh meat, seafood, and produce wrapping in retail due to its superior cling and stretch properties. Transmittance measurement also serves as an indirect monitor of plasticizer distribution and long-term optical stability.

PVDC and Multilayer Barrier Films

PVDC-coated or coextruded multilayer films provide oxygen and moisture barrier for extended shelf-life applications. Interlayer interfaces can introduce light scattering, so transmittance and haze testing confirms the optical quality of the layer structure.

Bio-based and Compostable Films

PLA and PBAT-based films may show elevated haze due to crystallinity or phase separation. Transmittance data supports performance claims, product development, and documentation for compostability certification programs.

Testing Items

• Total luminous transmittance (Tt): the percentage of incident visible light transmitted through the specimen
• Haze: the percentage of transmitted light that is scattered by more than 2.5 degrees from the incident direction, indicating loss of clarity
• Regular (specular) transmittance: transmitted light that passes without deviation, related to see-through clarity
• Spectral transmittance distribution across the 380 to 780 nm wavelength range
• Optional ultraviolet transmittance (200 to 380 nm) for evaluating light barrier performance toward photosensitive foods
• Optional transmittance retention after thermal aging, freezer storage, or contact with food simulants

Testing Methods

Applicable Standards

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, Procedure A (hazemeter) and Procedure B (spectrophotometer)
• ISO 13468-1 and ISO 13468-2: Determination of the total luminous transmittance of transparent materials using single-beam and double-beam integrating sphere methods
• ISO 14782: Determination of haze for transparent materials
• GB/T 2410: Chinese national standard for the determination of light transmittance and haze of transparent plastics
• JIS K 7361-1 and JIS K 7136: Japanese industrial methods for total luminous transmittance and haze

Hazemeter Method (Integrating Sphere Photometry)

A collimated light beam illuminates the specimen normal to its surface, and four successive luminous flux measurements are taken: T1 with no specimen and the sphere opening closed by the light-trap port cover, T2 with the specimen in place and the trap closed, T3 with no specimen and the trap open, and T4 with the specimen in place and the trap open. Total luminous transmittance is calculated as Tt = (T2 / T1) multiplied by 100, and haze is calculated as the quantity [(T4 / T2) minus (T3 / T1)] multiplied by 100.

Spectrophotometer Method

A UV-Visible spectrophotometer fitted with an integrating sphere accessory records the spectral transmittance of the specimen from 380 to 780 nm. The spectral data are weighted according to the CIE photopic luminous efficiency function and a standard illuminant, then integrated to obtain total luminous transmittance. This method is particularly useful when detailed spectral information, such as UV blocking behavior, is required.

Specimen Preparation and Conditioning

A minimum of three to five specimens should be cut from representative positions of the film roll, each large enough to fully cover the instrument aperture and free of creases, scratches, fingerprints, and embedded defects. Specimens are conditioned at 23 plus or minus 2 degrees Celsius and 50 plus or minus 5 percent relative humidity for at least 40 hours prior to measurement, and are mounted flat without tension or air bubbles.

Instrument Calibration and Reporting

The instrument is zeroed and referenced against an open-beam (air) measurement before testing and verified with certified reference materials where available. The final result is reported as the arithmetic mean of all valid specimens together with the standard deviation, specimen thickness, film material, conditioning history, and the specific standard method applied.

Applications

• Incoming and outgoing quality control for film extrusion and converting lines
• Retail display optimization for fresh meat, seafood, produce, and delicatessen packaging
• Light barrier assessment for photosensitive foods prone to photooxidation, such as high-fat products and dairy
• Research and development of new resins, slip agents, anti-fog masterbatches, and clarifier formulations
• Generation of optical performance data for food-contact material compliance dossiers and customer specifications
• Independent verification and comparison testing performed by accredited third-party laboratories

FAQ

What transmittance value is considered good for cling film?

High-quality PE or PVC cling film typically shows total luminous transmittance of approximately 90% or higher, with haze kept to a low single-digit percentage. Values vary with resin grade, thickness, and additives, so acceptance criteria should be agreed between supplier and purchaser based on the intended application.

What is the difference between transmittance and haze?

Transmittance quantifies how much light passes through the film, while haze quantifies how much of the transmitted light is scattered at wide angles. A film can show high transmittance yet poor see-through clarity if haze is elevated, so both parameters are usually reported together.

Which standard should be selected for testing?

ASTM D1003 is widely used in North America, ISO 13468 and ISO 14782 are common in international trade, and GB/T 2410 is typically requested for the Chinese market. All methods are technically aligned in principle, and results are broadly comparable when instrument geometry and specimen preparation are consistent.

Does film thickness affect the result?

Yes. Transmittance generally decreases slightly and haze increases as thickness rises because of bulk absorption and scattering. Cling film should always be tested at its actual use thickness, and the thickness should be stated in the test report.

Can colored, tinted, or anti-fog coated films be tested?

Yes. Total luminous transmittance measurement applies to any transparent or translucent film, including tinted and coated grades. For such products, reporting the full spectral transmittance curve is often more informative than a single integrated value.