Plastic Light Transmittance and Haze Testing: Experimental Methods, Standards, and Applications

Plastic light transmittance and haze testing is a critical optical performance evaluation for transparent and translucent polymeric materials widely used in packaging, automotive, electronics, lighting, and construction industries. This article provides a comprehensive technical overview of the experimental principles, applicable international standards, sample requirements, testing procedures, and practical applications of transmittance and haze measurement for plastic materials.

Technical Overview

Light transmittance and haze are two of the most important optical quality indicators for transparent and translucent plastic materials. The luminous transmittance (Tt) is defined as the ratio of the luminous flux transmitted through a specimen to the luminous flux incident upon it, expressed as a percentage. Haze (H), also known as milkiness in some contexts, is defined as the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam due to forward scattering within or at the surface of the specimen.

These two parameters describe different aspects of optical behavior. A material can exhibit high transmittance while simultaneously showing high haze, meaning that a large quantity of light passes through but the image-forming quality is poor. Conversely, a low-haze material preserves image clarity and see-through definition. The optical performance of plastics is governed by multiple factors, including polymer crystallinity, molecular orientation, the presence of additives such as fillers, nucleating agents, and impact modifiers, pigment content, surface roughness, and specimen thickness. A controlled laboratory experiment is therefore essential for objective material qualification, quality control, and research and development.

Modern light transmittance and haze experiments are performed using dedicated hazemeters or spectrophotometers equipped with integrating spheres, following recognized international methods such as ASTM D1003, ISO 13468, ISO 14782, GB/T 2410, and JIS K 7361. These procedures ensure reproducible, comparable results across accredited third-party laboratories and internal quality departments worldwide.

Testing Samples

Rigid Transparent Sheets and Panels

Common rigid samples include polymethyl methacrylate (PMMA, acrylic), polycarbonate (PC), polystyrene (PS), general-purpose and high-impact grades, polyethylene terephthalate (PET) and glycol-modified PET (PETG), rigid polyvinyl chloride (PVC), and transparent acrylonitrile butadiene styrene (ABS) or cycloolefin copolymer (COC) sheets. These materials are typically used for glazing, lighting diffusers, machine guards, and display windows.

Flexible Films and Thin Membranes

Flexible film samples include biaxially oriented polypropylene (BOPP), low-density and linear low-density polyethylene (LDPE/LLDPE), cast polypropylene (CPP), PVC films, PET films, polylactic acid (PLA) films, and multilayer laminated packaging films. Film samples require careful mounting to avoid wrinkles, air pockets, and surface contamination, as these artifacts artificially inflate measured haze values.

Injection-Molded and Thermoformed Parts

Finished components such as automotive light covers, instrument lenses, medical device windows, food containers, and transparent housings can be evaluated directly, provided the test area is sufficiently flat, uniform in thickness, and free of sink marks, gate vestige, flow lines, and molded-in stress birefringence.

Sample Preparation Requirements

• Recommended specimen dimensions are typically 50 mm × 50 mm, or circular disks of 50 mm diameter, to fully cover the standard 25 mm or larger measurement aperture.
• The test surface must be clean, dry, and free of fingerprints, dust, scratches, and protective film residue; cleaning should use lint-free wipes with an appropriate solvent that does not attack or swell the polymer.
• Specimens should be conditioned at standard laboratory atmosphere, typically 23 ± 2 °C and 50 ± 10% relative humidity, for a period of no less than 40 hours before measurement.
• Thickness must be reported along with results, because both transmittance and haze are thickness-dependent properties; comparison between materials is only valid at equivalent thickness.
• At least three to five specimens per material condition should be tested, and the arithmetic mean reported, to account for material inhomogeneity.

Testing Items

The core optical parameters measured in a plastic transmittance and haze experiment include:

• Total Luminous Transmittance (Tt): The total percentage of incident visible light that passes through the specimen, including both directly transmitted and diffusely transmitted components. Typical values range from approximately 92% for optically clear PMMA to below 60% for highly filled or pigmented materials.
• Haze (H): The percentage of transmitted light scattered more than 2.5 degrees from the incident direction. Optical-grade PMMA and PC typically show haze below 0.5–1%, while light-diffusing materials are intentionally formulated to reach haze values of 70–95% or higher.
• Diffuse Transmittance (Td): The transmitted flux that deviates from the specular direction, used to characterize light-scattering behavior in diffusion panels and backlit components.
• Parallel (Specular) Transmittance (Tp): The directly transmitted component that preserves image fidelity, calculated as the difference between total and diffuse transmittance.
• Optional Spectral Transmittance Curve: Wavelength-dependent transmittance from approximately 380 nm to 780 nm, useful for colored, tinted, or functional coated plastics.

Testing Methods

Applicable Standards

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, Method A uses a hazemeter and Method B uses a spectrophotometer; widely adopted in North America and global supply chains.
• ISO 13468-1 and ISO 13468-2: Determination of the total luminous transmittance of transparent materials, using an integrating sphere, with Part 1 covering single-beam and Part 2 covering double-beam instruments.
• ISO 14782: Determination of haze for transparent materials, defining the measurement geometry and the 2.5-degree scattered-light criterion.
• GB/T 2410: The Chinese national standard for the determination of light transmittance and haze of transparent plastics, technically aligned with ASTM D1003 and widely used for domestic compliance and product declarations.
• JIS K 7361-1 and JIS K 7136: Japanese industrial standards covering total luminous transmittance and haze of plastics, respectively, commonly referenced in East Asian markets.

Instrumentation and Principle

A standard hazemeter consists of a stable light source, typically a standard illuminant D65 or Illuminant A with CIE photopic correction, a collimated optical path, an integrating sphere with a high-reflectance inner coating, a light trap for specular-ray exclusion, and a photodetector with associated electronics. During measurement, four sequential readings of flux are collected: the incident flux, the total transmitted flux, the scattered flux with the specimen in place and the light trap open, and the instrumental scattered flux with the light trap closed. The total luminous transmittance is calculated as the ratio of total transmitted flux to incident flux multiplied by 100, while haze is calculated as the scattered transmitted flux divided by total transmitted flux, corrected for instrument scattering, multiplied by 100.

Experimental Procedure

• Calibrate and zero the instrument using certified reference standards traceable to national metrology institutes, verifying both transmittance and haze reference values.
• Condition the specimens and allow them to equilibrate in the test laboratory to prevent condensation and dimensional instability.
• Inspect each specimen visually and place it flat against the transmission port, ensuring full coverage of the aperture without stretching, bending, or trapping air bubbles beneath film samples.
• Record transmittance and haze readings at multiple positions across the specimen surface to capture spatial uniformity, particularly for extruded, coated, or embossed materials.
• Calculate the mean value and standard deviation for each parameter, report the test standard, illuminant, observer function, specimen thickness, and conditioning history together with the numerical results.

Key Factors Affecting Results

• Thickness: Increasing thickness generally reduces total transmittance and increases haze due to greater bulk scattering path length.
• Surface Condition: Scratches, texture, matte finishes, and embossed patterns dramatically raise measured haze even when bulk clarity is unchanged.
• Crystallinity and Additives: Semicrystalline polymers such as PP and PE scatter light at crystallite boundaries; antifog agents, slip agents, and pigments modify both parameters.
• Aging and Weathering: UV exposure, hydrolysis, and oxidation cause yellowing and microcracking, degrading transmittance and elevating haze over time, which is why these measurements are often integrated into durability studies.

Applications

• Packaging: Verifying the clarity of BOPP, PET, and PE films for retail packaging where product visibility drives consumer appeal, and confirming haze thresholds for matte or soft-touch finish films.
• Automotive: Qualifying headlamp lenses, tail-lamp covers, sunroof glazing, and instrument cluster windows against OEM optical specifications for transmittance, haze, and weathered performance.
• Lighting and Optics: Characterizing PMMA and PC diffuser panels and light guides, where a controlled balance between high total transmittance and engineered haze determines illumination efficiency and uniformity.
• Electronics and Display: Evaluating cover lenses, touch panel substrates, and transparent windows for devices where image sharpness and antiglare performance are critical.
• Construction and Agriculture: Assessing greenhouse films, polycarbonate multiwall sheets, and skylight glazing for daylight transmission and diffusion requirements that influence crop yield and building energy performance.
• Medical and Laboratory: Confirming the transparency of IV components, diagnostic cuvettes, blister packs, and sterile barriers that demand visual inspection capability.
• Solar and Energy: Measuring front-sheet films and encapsulant materials for photovoltaic modules, where transmittance loss directly translates into power output loss.
• Research and Quality Control: Supporting formulation development, process optimization for extrusion and injection molding, incoming material inspection, and batch-to-batch consistency verification.

FAQ

What is the difference between transmittance and haze?

Transmittance quantifies how much light passes through a material in total, while haze quantifies how much of that transmitted light is scattered away from the straight-through direction. A material can transmit a high percentage of light yet scatter it heavily, appearing bright but blurring the view of objects behind it.

Which standard should be selected: ASTM D1003, ISO, or GB/T?

Selection depends on the target market and customer specification. ASTM D1003 and GB/T 2410 are closely harmonized and widely accepted for general plastics, whereas ISO 13468 and ISO 14782 are preferred when international harmonization is required. Because instrument geometry and calculation details differ slightly between methods, the standard used must always be stated in the test report.

Does sample thickness affect the measured values?

Yes. Transmittance and haze are thickness-dependent properties. Thicker specimens produce longer optical paths, increasing absorption and scattering. Comparative evaluations should therefore be conducted on specimens of identical nominal thickness, and thickness must always accompany the reported result.

Can colored or translucent materials be tested?

Yes. The same instruments and standards apply to tinted, colored, and translucent plastics. For colored materials, spectral transmittance data across the visible wavelength range provides additional insight beyond the single photopic value.

What sample size is required?

A minimum specimen of 50 mm × 50 mm is generally recommended to cover the standard measurement port, although some instruments accept smaller apertures of 20–30 mm for finished parts. Specimens must be flat at the measurement area and free from curvature, which can deflect the light beam.

Why does the same material sometimes show different haze results between laboratories?

Small discrepancies can arise from differences in instrument geometry, sphere design, calibration standards, specimen conditioning, and surface handling. Using accredited third-party laboratories with traceable reference standards and consistent specimen preparation minimizes inter-laboratory variation and ensures reliable, comparable data.