Haze Testing of Optical Plastics: Standards, Methods, and Applications

Haze testing of optical plastics is a critical quality control procedure that quantifies the light-scattering behavior of transparent polymer materials such as polycarbonate, acrylic, and optical films. This article provides a comprehensive technical overview of the haze test, covering applicable standards such as ASTM D1003, ISO 14782, and GB/T 2410, common sample types, measurement principles, calculation methods, and typical industrial applications.

Technical Overview

Haze is defined as the percentage of transmitted light that, in passing through a transparent specimen, is scattered by more than 2.5 degrees from the direction of the incident beam. For optical plastics, haze is one of the most important optical performance indicators because it directly affects visual clarity, see-through quality, and the appearance of transparent or translucent components. The haze test is typically performed together with a measurement of total luminous transmittance, allowing manufacturers to fully characterize the light-transmission behavior of a material.

Optical plastic haze testing is governed by several internationally recognized standards, including ASTM D1003 (Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics), ISO 14782 (Plastics — Determination of Haze for Transparent Materials), ISO 13468-1 (Determination of the Total Luminous Transmittance of Transparent Materials), GB/T 2410 (the Chinese national standard for light transmittance and haze of transparent plastics), and the corresponding JIS standards such as JIS K 7136 and JIS K 7361-1. Accredited third-party laboratories routinely conduct haze tests according to these standards for material qualification, incoming inspection, and product certification purposes.

• Haze: the ratio of diffuse (scattered) transmittance to total luminous transmittance, expressed as a percentage.
• Total luminous transmittance: the percentage of incident light that passes through the specimen, including both diffuse and directly transmitted components.
• Key measurement criterion: only light scattered more than 2.5 degrees from the normal incident direction is counted as haze-contributing diffuse light.
• Common materials tested: PMMA (acrylic), PC (polycarbonate), PS, PET, PVC, COP/COC, TPU, and various optical-grade polymer films.

Testing Samples

Haze testing can be performed on a wide range of transparent and translucent plastic specimen forms. Because haze is strongly influenced by thickness, surface condition, and processing history, specimens must be representative of the actual material or product and must be free of dust, fingerprints, scratches, and other surface contamination.

Injection-Molded Plaques

Flat injection-molded plaques are the most common specimen format for resin characterization. Standard plaque thicknesses of 1 mm, 2 mm, and 3 mm are frequently specified so that haze values can be compared between materials on an equal-thickness basis. The molding conditions should be documented, since residual stress, cooling rate, and surface replication of the mold can all affect the measured haze.

Compression-Molded and Cast Sheets

For thermosetting materials, optical silicones, or materials where injection molding is impractical, compression-molded or cast sheets with polished surfaces may be used. Both surfaces of the sheet should be flat, parallel, and free of waviness and sink marks.

Polymer Films and Thin Sheets

Optical films used in displays, touch panels, and flexible packaging can be tested directly. Films must be mounted flat without wrinkles, air bubbles, or stretching, and haze results should always be reported together with the film thickness.

Finished Optical Components

Lenses, light guides, window covers, headlamp lenses, and other finished transparent parts can be evaluated, provided they present a substantially flat measurement area and fit the instrument aperture. Curved or textured parts may require flat witness specimens molded under identical conditions.

Testing Items

A standard optical plastic haze test typically reports the following parameters:

• Haze (percent): the primary result, calculated as diffuse transmittance divided by total transmittance multiplied by 100.
• Total luminous transmittance (percent): the overall light-transmitting capability of the specimen.
• Diffuse transmittance (percent): the scattered portion of transmitted light.
• Regular (specular) transmittance: the directly transmitted portion, obtained as the difference between total and diffuse transmittance.
• Specimen thickness and conditioning state: mandatory reporting elements, since haze increases measurably with thickness.

Testing Methods

Hazemeter Method (Integrating Sphere)

The most widely used approach employs a hazemeter based on an integrating sphere optical system. A collimated beam of light, typically corresponding to CIE Illuminant C or D65 with a photopic-response detector, is directed through the specimen. A light trap (or an opaque port cover) is used to exclude the unscattered beam when the diffuse component is measured. In accordance with ASTM D1003, four sequential readings are taken: the incident beam without a specimen, the total transmittance with the specimen in place, the instrumental scatter without a specimen and with the light trap engaged, and the diffuse transmittance with the specimen in place and the light trap engaged.

Spectrophotometer Method

An alternative method uses a UV-Visible spectrophotometer equipped with an integrating sphere attachment. The transmittance spectra are scanned across the visible wavelength range, from which photometrically weighted haze and total transmittance values are computed. This method is particularly useful when wavelength-dependent scattering behavior must be investigated.

Calculation of Results

Total luminous transmittance is calculated as the ratio of the total transmitted reading to the incident reading. Haze is calculated as the ratio of the diffuse transmittance to the total transmittance, with instrumental scatter corrections applied as specified by the standard. The final haze value is expressed as a percentage to one decimal place in most commercial reports.

Instrument Calibration and Specimen Conditioning

Before testing, the hazemeter must be calibrated using certified haze and transmittance reference standards traceable to national metrology institutes. Specimens are normally conditioned at 23 ± 2 °C and 50 ± 10% relative humidity for a defined period, and both surfaces are cleaned with lint-free wipes immediately before measurement. Multiple specimens (typically three to five) are tested and averaged to improve result reliability.

Applications

Haze test data for optical plastics are used across many industries wherever transparency, clarity, or controlled light diffusion is required:

• Display and electronics: optical films, touch panel covers, PMMA and PC light guide plates, and transparent window lenses for consumer electronics.
• Automotive: headlamp and taillamp lenses, instrument cluster covers, panoramic roof glazing, and interior display windows.
• LED lighting: diffuser plates and lamp covers where haze is deliberately engineered to achieve uniform illumination while maintaining high transmittance.
• Optical instruments: lenses, prisms, sight glasses, and protective windows requiring low-haze, high-clarity materials.
• Packaging: transparent films and rigid containers where product visibility influences consumer perception.
• Medical devices: transparent tubing, sterile packaging, and diagnostic equipment windows.
• Material development: comparing resin grades, evaluating the effect of additives, fillers, colorants, and crystallinity, and validating processing parameters such as mold temperature and injection speed.

FAQ

What is the difference between haze and transmittance?

Transmittance measures how much light passes through a specimen, while haze measures how much of that transmitted light is scattered away from the direct beam. A material can have high transmittance but high haze (diffusive), or high transmittance and low haze (fully transparent), so the two parameters characterize different optical properties and are normally reported together.

Which test standard should be selected?

ASTM D1003 is widely used in North American markets, ISO 14782 and ISO 13468-1 are common for international supply chains, GB/T 2410 is used for the Chinese market, and JIS K 7136 and JIS K 7361-1 apply to Japanese specifications. The standards are technically consistent in principle, but the choice should match customer requirements, product specifications, and the target regulatory market.

How does specimen thickness affect haze results?

Haze generally increases with thickness because a longer optical path produces more volumetric scattering. For this reason, haze values must always be reported with the specimen thickness, and comparisons between materials are only valid at equal thickness.

What causes high haze in optical plastics?

Common causes include surface roughness from poor mold polishing or abrasion, internal scattering from crystalline structures, incompatibilized additive phases, dispersed particles such as pigments or fillers, flow lines and residual stress, and contamination or dust on the specimen surface.

What sample size and quantity are required for testing?

A typical specimen is a flat plaque or film section of approximately 50 mm × 50 mm that fully covers the instrument aperture, with three to five replicate specimens recommended. Accredited third-party laboratories can provide specific dimensional requirements based on the selected standard and the instrument configuration.

What is a typical acceptable haze level?

Acceptance limits depend entirely on the application. Optical-grade PMMA and PC can achieve haze below 0.5 to 1 percent at standard thicknesses, general transparent covers often specify haze below 2 to 3 percent, and LED diffuser materials are intentionally designed with haze values above 50 percent to distribute light uniformly.