Haze evaluation is a fundamental optical quality control test for display panels, quantifying the light scattering that degrades visual clarity, contrast, and readability. This technical guide explains the principles of haze measurement, applicable international standards such as ASTM D1003 and ISO 14782, sample types, testing procedures, and typical applications across cover glass, optical films, and finished display modules.
Technical Overview
Haze, in the context of display panel evaluation, is defined as the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam. It is expressed as the ratio of diffuse transmittance to total luminous transmittance, and it directly characterizes the degree of light scattering introduced by a material or surface structure. In a display system, excessive haze softens images, reduces perceived sharpness and contrast, and can cause a milky or frosted appearance, while insufficient haze on certain functional films can produce unacceptable glare and specular reflections.
Haze is calculated using the following relationship: Haze (%) = (Diffuse Transmittance / Total Transmittance) x 100, where total transmittance includes both regularly transmitted (specular) light and diffusely scattered light. Modern display panels are multi-layer stacks consisting of cover glass, touch sensor layers, polarizers, adhesives, display cells, and backlight or optical films, and each layer contributes to the cumulative haze of the assembled module. For this reason, haze evaluation is performed at both the component level and the module level, using standardized photometric methods and calibrated reference materials.
Testing Samples
Cover Glass and Chemically Strengthened Glass
Cover glass samples, including ion-exchange strengthened aluminosilicate glass used in smartphones, tablets, and automotive displays, are evaluated for baseline haze and transmittance. Both uncoated and coated configurations are tested, with specimens typically cut to sizes compatible with the measurement aperture of the hazemeter.
Anti-Glare (AG) and Anti-Reflective (AR) Coated Substrates
AG treatments create controlled surface micro-structures that deliberately scatter specular reflections, making haze a primary specification parameter. AR multi-layer coatings, in contrast, must maintain very low haze to preserve image sharpness. Evaluation of coated substrates verifies that scattering remains within the designed window for the target application.
Polarizer Films
Polarizing films for LCD panels are assessed for haze and parallel transmittance, since excessive scattering in the polarizer reduces brightness and degrades black-state performance. Both raw tri-acetate cellulose (TAC) films and complete polarizer assemblies can be measured.
Optical Films for Backlight Units
Diffuser films, prism or brightness enhancement films, reflective films, and protective films are core haze-controlled components. Diffuser films are intentionally specified with high haze values, while brightness enhancement films require tightly bounded haze to balance gain and clarity.
Touch Sensor Panels and ITO-Coated Glass
Transparent conductive substrates, including ITO-coated glass and ITO film on PET, are tested because conductive layer crystallinity, etching patterns, and micro-defects can introduce measurable scattering that affects the transmitted image.
Optically Clear Adhesives (OCA) and Finished Display Modules
OCA films and laminated touch-display assemblies are evaluated to confirm that the lamination process, bubble content, and adhesive uniformity do not add unacceptable haze. Complete display modules may be assessed for integrated optical performance.
Testing Items
- Haze (diffuse-to-total transmittance ratio, reported in percent)
- Total luminous transmittance (Tt) over the visible spectrum
- Diffuse transmittance (Td)
- Parallel (specular) transmittance
- Spectral transmittance distribution from 380 nm to 780 nm
- Gloss at 60 degrees and 20 degrees (complementary surface metric)
- Clarity or see-through quality assessment for high-definition applications
- Post-reliability haze shift, such as haze increase after Taber abrasion, thermal aging, or humidity exposure
Testing Methods
Haze evaluation is primarily performed using two instrument configurations described in ASTM D1003: Method A using a dedicated hazemeter, and Method B using a spectrophotometer equipped with an integrating sphere. In both configurations, the specimen is illuminated with a standardized light source approximating CIE Illuminant A, and photometric detection follows the CIE photopic response. A light trap positioned at 2.5 degrees from the optical axis excludes near-regular transmitted light so that only wide-angle scattered light is registered as diffuse transmittance.
The measurement sequence generally follows these steps:
- Condition specimens at 23 +/- 2 degrees Celsius and 50 +/- 5 percent relative humidity to stabilize surface and bulk optical properties.
- Perform zero calibration with the light trap in place to determine the instrument baseline, then set full-scale transmittance using the unobstructed beam or a calibrated reference standard.
- Mount the specimen flush against the measurement port, avoiding tilt, dust, fingerprints, and air gaps that introduce measurement error.
- Record total transmittance, diffuse transmittance, and computed haze; for non-uniform materials such as patterned touch sensors or textured AG surfaces, take multiple readings at different positions and report the average and range.
- Correct for instrument agreement using nationally traceable haze and transmittance reference standards.
The principal standards applied to display-related haze evaluation include ASTM D1003 for haze and luminous transmittance of transparent materials, ISO 14782 for the determination of haze of transparent plastics, ISO 13468-1 and ISO 13468-2 for total luminous transmittance, GB/T 2410 as the corresponding Chinese national method, JIS K 7361-1 and JIS K 7361-2 for transmittance and haze respectively, and ASTM D523 or ISO 2813 for complementary gloss measurement. ASTM D1044 is applied when haze generation through Taber abrasion is part of a durability or coating hardness assessment. Because method definitions, light source specifications, and scattering angle conventions differ slightly between standards, the applicable standard must be agreed between supplier and purchaser before testing.
Applications
- Incoming quality control of cover glass, polarizers, and optical films at display panel manufacturers and assembly houses
- Development and optimization of AG and AR coating processes, including spray, etching, and deposition parameters
- Verification of lamination quality for touch panels and OCA bonding processes
- Durability and reliability studies, including haze growth after abrasion, ultraviolet exposure, thermal cycling, and damp heat aging
- Automotive display qualification, where readability under sunlight and controlled glare behavior are safety-relevant requirements
- Supplier qualification, specification arbitration, and independent verification by accredited third-party laboratories
- Research on novel materials such as anti-reflective moth-eye structures, flexible polymer covers, and micro-lens diffuser films
FAQ
What haze value is typical for display cover glass? Polished and AR-coated cover glass generally exhibits haze below 0.5 to 1 percent, while AG-treated cover glass is intentionally specified in a broad range, commonly from several percent up to more than 20 percent, depending on whether the priority is glare suppression or image sharpness.
What is the difference between haze and transmittance? Transmittance quantifies how much light passes through the specimen in total, while haze quantifies what fraction of that transmitted light has been scattered beyond 2.5 degrees. A material can be highly transmissive yet hazy, or less transmissive yet optically clear.
Why is the 2.5 degree angle used as the boundary? The 2.5 degree acceptance cone is the standardized convention established in ASTM D1003 and adopted by ISO, GB, and JIS methods. Light scattered within this narrow cone has negligible effect on perceived image blur, while light scattered beyond it contributes to haze as visually experienced.
How should specimens be prepared? Specimens should be clean, free of scratches and fingerprints, flat, and larger than the instrument aperture. Curved or rigid finished parts may require specially adapted fixtures or sectioning, and orientation relative to extrusion or coating direction should be recorded for anisotropic films.
Which standard should be selected for reporting? ASTM D1003 and ISO 14782 are the most widely referenced methods for component-level haze, with GB/T 2410 and JIS K 7361 series used for specific regional supply chains. Because numerical results can differ slightly between methods, test reports should always state the standard, instrument configuration, light source, number of measurement points, and specimen conditions.