Haze Testing of Plastic Sheets: Standards, Methods, and Applications

Haze testing of plastic sheets quantifies the amount of transmitted light that is scattered as it passes through transparent or translucent materials such as PMMA, polycarbonate, and PET panels, directly affecting optical clarity and product quality. This article explains the testing principle, applicable international standards including ASTM D1003, ISO 14782, and GB/T 2410, typical sample types, measurement procedures, and common industrial applications for accredited third-party laboratories.

Technical Overview

Haze is defined as the percentage of transmitted light that, in passing through a plastic specimen, is scattered by more than 2.5 degrees from the average incident beam direction. It is calculated as the ratio of diffuse transmittance to total luminous transmittance, expressed as a percentage. A higher haze value indicates a milkier, less transparent appearance, while a lower value indicates greater see-through clarity.

In plastic sheets and boards, haze originates from several sources, including surface roughness, scratches, internal voids, crystalline structures, dispersed additives, fillers, and processing defects. Haze should not be confused with total luminous transmittance, which measures how much light passes through the specimen regardless of scattering direction. A material can transmit a high percentage of light while still exhibiting high haze, as is the case with light-diffusing panels used in LED lighting fixtures.

Measurement is performed using a hazemeter or a spectrophotometer equipped with an integrating sphere, following standardized illuminant and observer conditions specified by CIE. Regular calibration with reference standards and careful control of specimen surface condition are essential to obtaining reproducible results.

Testing Samples

PMMA (Acrylic) Sheets

Cast and extruded PMMA sheets are widely tested for haze and transmittance due to their use in lighting, signage, and glazing. Surface quality, protective film residue, and thickness uniformity strongly influence the measured haze value.

Polycarbonate (PC) Sheets

Transparent and textured polycarbonate sheets, including multiwall and corrugated profiles used for roofing and skylights, require haze and transmittance verification to confirm optical grade quality and weathering performance after UV exposure.

PVC Sheets

Rigid transparent PVC sheets used in packaging, thermoformed parts, and technical applications are evaluated to ensure consistent optical properties between production batches.

PET and PP Sheets

Amorphous PET sheets and clarified polypropylene sheets used in packaging and thermoforming are tested to control crystallinity-related haze, which can increase during processing or storage.

Light-Diffusing Plates

Diffuser plates containing optical additives are intentionally engineered for controlled haze. Testing confirms that the diffusion level falls within the specified tolerance for uniform illumination in luminaires and backlight units.

Testing Items

• Haze value, expressed as a percentage of diffuse transmittance relative to total transmittance
• Total luminous transmittance under specified standard illuminant conditions
• Diffuse transmittance, reported directly or derived from the haze calculation
• Clarity or see-through quality for applications requiring image resolution, where applicable
• Thickness measurement and surface condition documentation as supporting data

Testing Methods

ASTM D1003

ASTM D1003, Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, is the most widely referenced method. Method A uses a hazemeter with an integrating sphere, while Method B uses a spectrophotometer. The method covers both haze and total transmittance in a single measurement sequence.

ISO 14782

ISO 14782, Plastics — Determination of Haze for Transparent Materials, defines haze as the percentage of regular transmitted light scattered more than 2.5 degrees. It specifies instrumentation geometry, calibration procedures, and reporting requirements consistent with international metrology practice.

GB/T 2410

GB/T 2410 is the Chinese national standard for determining light transmittance and haze of transparent plastics. It is technically equivalent in principle to ASTM D1003 and is commonly required for products sold in the Chinese market.

JIS K 7136 and JIS K 7361

These Japanese industrial standards specify haze and luminous transmittance determination respectively, aligned with ISO 14782 and ISO 13468, and are frequently requested for automotive and electronics supply chains.

Specimen Preparation and Conditioning

Specimens are typically cut to at least 50 mm by 50 mm squares or circles, free of scratches, fingerprints, and dust, with protective films removed prior to testing. Conditioning is usually performed at 23 ± 2 °C and 50 ± 5 % relative humidity in accordance with ISO 291 or ASTM D618. Thickness is recorded because haze generally increases with specimen thickness.

Applications

• LED lighting: quality control of light guide panels, diffuser plates, and lamp covers for uniform brightness
• Architecture and construction: optical verification of glazing, skylights, canopies, and transparent roofing sheets
• Displays and electronics: cover lenses, instrument windows, and touch panel substrates requiring low haze
• Automotive: transparent interior trim, glazing components, and headlamp diffusers
• Agriculture: greenhouse covering films and rigid sheets balancing light transmission with diffusion
• Packaging and medical: transparent blister packs, trays, and rigid containers where product visibility matters

FAQ

What is the difference between haze and transmittance?

Transmittance measures the total amount of light passing through the specimen, while haze measures only the scattered portion of that transmitted light. A diffuser plate may have 85 percent transmittance with 95 percent haze, meaning most light passes through but is heavily scattered.

What haze value is considered acceptable?

Acceptance limits depend on application. Optical-grade sheets for displays often require haze below 1 to 2 percent, general glazing materials may allow 2 to 5 percent, and engineered diffusing plates may intentionally specify haze above 80 percent. Specification limits are agreed between buyer and supplier.

Why do haze results vary between laboratories?

Variations can arise from differences in instrument geometry, illuminant and observer settings, calibration reference standards, specimen surface cleaning, and ambient conditioning. Using a single standard method, such as ASTM D1003 Method A with documented calibration, minimizes interlaboratory discrepancies.

Does sample thickness affect the haze result?

Yes. Haze generally increases with thickness because light travels a longer path and scatters more within the material and at internal interfaces. Reported results should always state specimen thickness, and comparisons should be made at equivalent thickness.

Can textured or embossed sheets be tested?

Textured surfaces scatter light by design, so measured haze is reported for the sheet as manufactured. Both textured and smooth surfaces should be measured and reported, since the two faces often produce different values.

How should specimens be shipped for testing?

Specimens should be cut slightly larger than the required aperture, kept free of scratches and abrasion, separated with clean interleaving material, and shipped flat with protective packaging to prevent stress marks that could alter the measured haze.