Plastic Light Transmittance Test Protocol: Standards, Sample Requirements, and Testing Methods

This plastic light transmittance test protocol defines the standardized procedures, sample requirements, and evaluation criteria for measuring the total luminous transmittance and haze of transparent and translucent plastic materials. Based on internationally recognized standards including ASTM D1003, ISO 13468, ISO 14782, and GB/T 2410, the scheme applies to PMMA, PC, PS, PET, PP, and PE sheets and films used in automotive glazing, LED lighting, displays, and packaging. Accredited third-party laboratories and in-house quality teams can follow this plan to achieve accurate, repeatable optical characterization of plastic products.

Technical Overview

Light transmittance is a fundamental optical property of transparent plastics, defined as the percentage of incident luminous flux that passes through a specimen. It is measured using the CIE standard illuminant A (correlated color temperature of 2856 K) weighted by the photopic response of the CIE 1931 standard observer over the visible wavelength range of 380 nm to 780 nm. This test protocol specifies how plastic materials are evaluated for total luminous transmittance, haze, and related optical parameters using integrating-sphere hazemeters and ultraviolet-visible spectrophotometers in accredited third-party laboratories or in-house quality control facilities.

The scheme is aligned with the following internationally recognized standards:

• ASTM D1003 – Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics (Method A and Method B)
• ISO 13468-1 and ISO 13468-2 – Determination of the total luminous transmittance of transparent materials using single-beam and double-beam instruments
• ISO 14782 – Determination of haze for transparent materials
• GB/T 2410 – Determination of light transmittance and haze of transparent plastics
• JIS K 7361-1 and JIS K 7136 – Japanese industrial equivalents for luminous transmittance and haze

Testing Samples

The protocol covers three principal categories of plastic test specimens. Specimen geometry, surface condition, and conditioning history directly influence optical results and must be documented in the test report.

Rigid Transparent Sheets and Panels

Extruded or cast sheets of PMMA (acrylic), PC (polycarbonate), PS (polystyrene), PETG, and glass-clear PP with thicknesses typically ranging from 0.5 mm to 10 mm. Specimens should be cut into squares or circles of at least 50 mm by 50 mm so that they fully cover the instrument measurement aperture, which is commonly 20 mm to 30 mm in diameter.

Flexible Plastic Films

PE, PP, BOPP, PET, PVC, and multilayer composite films used in packaging, agriculture, and display applications. Films thinner than 0.1 mm must be mounted flat and free of wrinkles, air pockets, and static attraction. Multiple layers must not be superimposed unless the laminated structure itself is the test object.

Molded Optical Components and Plaques

Injection-molded plaques, light guide plates, lenses, and transparent covers. Curved or textured parts should be sectioned or measured on flat representative areas. Where component geometry prevents direct measurement, flat witness plaques molded under identical processing conditions are recommended.

Specimen Conditioning and Preparation

• 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 agreed.
• Surfaces must be clean and free from dust, fingerprints, scratches, sink marks, and release agents. Wipe gently with a lint-free cloth and, if compatible with the polymer, with isopropyl alcohol.
• Measure and record specimen thickness at a minimum of five locations; because transmittance decreases with thickness, thickness must accompany every reported result.
• Prepare at least three specimens per material condition, and preferably five, so that mean values and scatter can be reported.

Testing Items

Core Optical Parameters

• Total luminous transmittance (Tt): the ratio of total transmitted luminous flux to incident luminous flux, expressed as a percentage, including both regular and diffuse components.
• Haze (wide-angle scattering, Td): the percentage of transmitted light that is scattered by more than 2.5 degrees from the incident beam direction, quantifying milkiness and loss of see-through clarity.
• Regular (specular) transmittance: the flux transmitted without deviation, calculated as total transmittance minus diffuse transmittance.
• Diffuse transmittance: the scattered component of transmission, critical for lighting diffusers and anti-glare products.
• Spectral transmittance curve: transmittance as a function of wavelength from 380 nm to 780 nm, useful for tinted and wavelength-selective materials.

Supplementary Optical Parameters

• Yellowness index (YI) in accordance with ASTM E313, to track optical degradation after heat or UV exposure.
• CIE color coordinates (L*, a*, b*) in accordance with ASTM E308 or ISO 11664 for color quality control of transparent articles.
• Transmittance retention after artificial weathering in accordance with ISO 4892 or ASTM G154, comparing aged versus unaged specimens.

Typical reference values for well-processed materials include: PMMA sheets 92 % to 93 % transmittance, PC sheets 88 % to 90 %, and general-purpose PS 88 % to 90 %. Automotive glazing is commonly regulated at a minimum of 70 % luminous transmittance.

Testing Methods

Method A: Integrating-Sphere Hazemeter (ASTM D1003 Method A, ISO 14782)

A collimated light beam illuminates the specimen, and an integrating sphere collects the transmitted flux. Four sequential measurements are taken: incident flux (T1), total transmitted flux with the specimen in place (T2), sphere-scattered flux with a light trap excluding the regular beam (T3), and specimen-scattered flux with both the specimen and the trap in position (T4).

• Total luminous transmittance: Tt = (T2 / T1) × 100 %
• Haze: Td = [(T4 / T2) − (T3 / T1)] × 100 %
• Instrument geometry: unscattered incident beam within 1.0 to 1.3 degrees half-angle; light trap acceptance half-angle of approximately 2.5 degrees.

Method B: Spectrophotometer Method (ASTM D1003 Method B, ISO 13468)

A UV-Vis spectrophotometer, preferably with an integrating sphere accessory, scans the specimen from 380 nm to 780 nm at intervals of 5 nm or finer. The spectral transmittance data are weighted by the CIE photopic luminous efficiency function V(λ) and the spectral distribution of standard illuminant A, then integrated to yield total luminous transmittance. Method B is preferred for tinted, spectral-selective, or moderately absorbing materials because the full spectral curve is retained.

General Test Procedure

• Step 1 – Instrument verification: warm up the light source, verify wavelength and photometric accuracy using certified reference filters or calibration plaques traceable to national metrology institutes.
• Step 2 – Baseline: perform a 100 % transmittance calibration with air in the beam path and a 0 % calibration with a full light block.
• Step 3 – Specimen mounting: place the conditioned specimen normal to the beam at the sphere port, ensuring full aperture coverage and identical orientation of any surface-textured side between specimens.
• Step 4 – Measurement: record transmittance and haze for each specimen at 23 ± 2 °C ambient temperature, avoiding condensation on cold specimens.
• Step 5 – Reporting: calculate the arithmetic mean, maximum, and minimum for all specimens, and report mean thickness, standard reference, instrument type, and specimen orientation.

Applications

Light transmittance data generated under this protocol support design, certification, and quality control across multiple industries:

• Automotive: windshield and side glazing compliance with the widely applied 70 % minimum transmittance requirement, lamp lenses, sunroofs, and instrument cluster covers.
• Lighting: LED diffuser plates, light guide plates, and lamp shades where the balance between transmittance and haze determines illumination uniformity and efficiency.
• Displays and electronics: cover lenses, touch panel substrates, protective windows, and transparent housings for sensors and infrared devices.
• Packaging: clear films, thermoformed blister packs, bottles, carton windows, and medical infusion bags where product visibility is a functional requirement.
• Construction and agriculture: skylights, polycarbonate corrugated sheets, and greenhouse films evaluated for light admission and diffusion performance.
• Material development: quantifying transmittance retention after UV and xenon-arc weathering, heat aging, and chemical exposure as part of durability studies.

FAQ

What is the difference between light transmittance and haze?

Transmittance measures how much visible light passes through the specimen regardless of direction, while haze measures the portion of that transmitted light scattered more than 2.5 degrees from the original beam path. A lighting diffuser may show high haze with moderate transmittance, whereas an optical window requires both high transmittance and very low haze.

Which standard should be selected for my product?

ASTM D1003 and GB/T 2410 are widely used for sheet and film qualification in general manufacturing, ISO 13468 combined with ISO 14782 is common for international supply chains, and JIS K 7361-1 plus JIS K 7136 serve the Japanese market. All four approaches yield comparable results when geometry, illuminant, and observer conditions are matched, and the chosen standard should be stated in the purchase specification.

How does specimen thickness affect the result?

Transmittance decreases and haze often increases with thickness due to bulk absorption and scattering. Results are only comparable at equal thickness, so thickness must always be reported alongside the transmittance value.

Can translucent or colored plastics be tested?

Yes. Translucent materials are measured for total and diffuse transmittance, while colored materials benefit from the spectrophotometer method, which preserves the full spectral curve and allows colorimetric calculations alongside transmittance.

How many specimens are required, and what is the typical turnaround?

A minimum of three conditioned specimens per material is recommended, with five preferred for statistical confidence. Routine measurement is rapid, and most projects are completed within three to five working days including conditioning, with weathering-related studies requiring additional exposure time.

How should results be interpreted for acceptance?

Compare measured mean transmittance and haze against product specification limits, regulatory minima such as the 70 % glazing requirement, or benchmark values for the resin family. Significant deviations from reference values typically indicate contamination, moisture uptake, improper processing, or surface defects, and warrant root-cause investigation.