Display material lightfastness testing evaluates the ability of optical films, color resists, coatings, and other display components to resist fading, yellowing, and chromaticity drift under prolonged light exposure. By using accelerated xenon arc or UV fluorescent weathering methods in accordance with ISO 105-B02, ISO 4892, ASTM G155, and related GB standards, accredited third-party laboratories help manufacturers quantify color difference (ΔE), gray scale ratings, and optical property changes before products reach the market. This article explains the sample types, test items, methodologies, and applications of lightfastness testing for display materials.
Technical Overview
Lightfastness, also known as colorfastness to light, describes a material's capacity to maintain its original color and optical characteristics when exposed to radiant energy over time. For display materials, photochemical degradation is a critical failure mode: ultraviolet and visible radiation can break down organic dyes, pigments, polymers, and adhesive layers, resulting in fading, yellowing, haze formation, delamination, and measurable shifts in chromaticity coordinates.
Because the service life of a display may span five to ten years or more, natural exposure testing is impractical for product development cycles. Accelerated lightfastness testing therefore uses controlled laboratory light sources—typically filtered xenon arc lamps or fluorescent UV lamps—to reproduce and intensify the photodegradation mechanisms of sunlight, including sunlight filtered through window glass or display cover layers. Test results are expressed through quantitative colorimetric parameters such as CIELAB color difference (ΔE*ab), gray scale ratings for color change, and changes in transmittance, haze, and yellowness index.
Lightfastness testing for display materials is generally performed according to internationally recognized frameworks, including the ISO 105-B series (textile-derived colorfastness methods widely applied to colored materials), ISO 4892 (plastics—methods of exposure to laboratory light sources), ASTM G151, ASTM G154, and ASTM G155 (general and specific accelerated exposure practices), together with their Chinese national standard (GB) equivalents such as GB/T 8427 and GB/T 16422.2. Accredited third-party laboratories conduct these tests under ISO/IEC 17025 quality systems to ensure traceable, reproducible results for R&D validation, quality control, and certification purposes.
Testing Samples
Color Filter Materials and Color Resists
Red, green, and blue (RGB) color resists used in LCD and OLED color filter manufacturing are among the most light-sensitive display materials. Pigment-dispersed photoresists and dye-based resists are tested to verify that filter spectral transmittance and chromaticity remain stable under long-term illumination, since even minor fading alters white balance and color gamut.
Polarizer Films
Iodine-based and dye-based polarizing films, including polarization axis stability and transmittance, are evaluated for photo-induced degradation. Dye-type polarizers are frequently specified for automotive and outdoor displays precisely because of their superior lightfastness, which must be demonstrated through testing.
OLED and Quantum Dot Materials
Emissive organic layers, host and dopant materials, quantum dot enhancement films (QDEF), and encapsulation stacks are tested for photostability, as UV and blue light exposure can accelerate aging, reduce luminance, and shift emission spectra.
Optical Adhesives and Coatings
Optically clear adhesives (OCA), pressure-sensitive adhesives, anti-glare (AG), anti-reflective (AR), anti-fingerprint (AF), and hard coatings are assessed for yellowing, haze development, cracking, and adhesion loss after light exposure.
Backlight and Functional Films
Diffuser sheets, reflective films, brightness enhancement films (prism films), light guide plates, and black matrix materials are tested to confirm the stability of transmittance, reflectance, and dimensional integrity.
Inks, Logos, and Decorative Layers
Printing inks, silk-screen legends, decorative textures, and light-shielding layers applied to display modules are evaluated for fading and discoloration consistent with their end-use light environment.
Testing Items
Lightfastness test programs for display materials typically include the following evaluations, performed before and after defined exposure intervals:
- Color difference (ΔE*ab, ΔL*, Δa*, Δb*) measured with a spectrophotometer or colorimeter in accordance with CIE 15 and ISO 11664 conventions
- Gray scale rating for color change, graded 1 to 5 in half-step increments per ISO 105-A02 and GB/T 250
- Lightfastness grade assessment against blue wool reference fabrics per ISO 105-B08 where applicable
- Transmittance and haze changes per ASTM D1003, ISO 13468, and ISO 14782
- Yellowness index (YI) and whiteness index per ASTM E313
- Chromaticity coordinate shift (CIE 1931 x,y or CIE 1976 u',v') for color-critical components
- Spectral power distribution and spectral transmittance curves across the visible wavelength range
- Visual inspection for fading, blistering, cracking, delamination, and surface defects under controlled lighting
- Functional properties such as polarization efficiency, luminance retention, and adhesion strength after exposure
Testing Methods
Xenon Arc Lamp Exposure
Filtered xenon arc testing is the most widely used method because a xenon source with appropriate daylight filters closely matches the full solar spectrum, including ultraviolet, visible, and infrared energy. Common references include ISO 105-B02, ISO 4892-2, ASTM G155, GB/T 8427, and GB/T 16422.2. Typical parameter sets involve irradiance levels such as 0.35 W/m² at 340 nm (daylight filter) or 1.10 W/m² at 420 nm (window glass filter), black panel or black standard thermometer temperatures of 50–65 °C, chamber temperatures of 38–45 °C, and relative humidity of 30–60 percent, with exposure durations ranging from tens to several hundreds of hours depending on the intended application.
Fluorescent UV Lamp Exposure
Fluorescent UV condensation testing per ISO 4892-3, ASTM G154, and GB/T 16422.3 uses UVA-340 lamps to reproduce the shortwave UV portion of sunlight or UVB-313 lamps for more severe screening. This method is cost-effective for comparing the relative photostability of material formulations, although it does not replicate the visible spectrum and is therefore best suited to UV-sensitive degradation studies.
Daylight and Behind-Glass Exposure
For correlation and benchmarking, natural exposure methods such as ISO 105-B01 (colorfastness to daylight) and outdoor behind-glass procedures can be used to establish a reference baseline against accelerated laboratory results.
Standard Test Procedure
- Specimen preparation: materials are cut to specified dimensions (commonly 50 mm × 100 mm or per the device requirement), mounted on inert holders, and conditioned in a standard atmosphere
- Baseline measurement: initial color, transmittance, haze, and chromaticity are recorded using calibrated instruments
- Exposure: specimens are placed in the lightfastness chamber with a portion masked as an unexposed control; radiometric calibration ensures accurate radiant exposure dosing
- Intermediate and final measurement: colorimetry is repeated after defined exposure cycles to construct a degradation-versus-dose curve
- Evaluation: ΔE*ab is calculated, gray scale ratings are assigned by comparison with the ISO 105-A02 scale, and pass/fail judgment is made against product specifications
Applications
Lightfastness testing supports product development and qualification across the entire display industry:
- Consumer electronics: smartphones, tablets, notebook computers, and televisions, where display appearance and color accuracy must remain stable over years of use
- Automotive displays: instrument clusters, center stack displays, and rear-seat entertainment screens face intense sunlight through windshields and windows, making window-glass-filtered xenon testing essential for interior components
- Outdoor digital signage and information displays: high-brightness displays operating under direct or indirect solar radiation require verified photostability of filters, films, and coatings
- Wearable and mobile devices: smartwatches, fitness bands, and AR/VR optical components exposed to both ambient light and strong internal light sources
- Industrial, medical, and marine instrumentation: displays used in harsh lighting environments or with extended service lifetimes
- Materials R&D and supplier qualification: comparative evaluation of pigments, dyes, resins, adhesives, and coating formulations during development and incoming inspection
- Regulatory and customer compliance: demonstrating conformity with manufacturer specifications, IEC display reliability frameworks, and industry qualification requirements
FAQ
What is display material lightfastness testing?
It is an accelerated laboratory test that exposes display materials such as color resists, polarizers, optical films, adhesives, and coatings to controlled xenon arc or UV radiation in order to measure their resistance to light-induced color change, yellowing, and optical degradation. Results are reported as color difference (ΔE*ab), gray scale rating, or lightfastness grade.
Which standard should be selected for my material?
For full-spectrum simulation, ISO 105-B02, ISO 4892-2, or ASTM G155 xenon arc methods are recommended, with window glass filters when the material is used behind cover glass. For UV-focused screening, ISO 4892-3 or ASTM G154 fluorescent UV methods are appropriate. Chinese national equivalents GB/T 8427 and GB/T 16422.2/.3 align with the corresponding ISO procedures.
How is the test result judged?
Judgment is typically based on the allowable ΔE*ab value and minimum gray scale rating defined in the product specification—for example, a gray scale rating of 4 or higher, or ΔE*ab below a specified limit after a stated exposure dose. Changes in transmittance, haze, and yellowness index are compared against acceptance thresholds where required.
How long does testing take?
Exposure durations commonly range from 24 to several hundred hours depending on the method, irradiance level, and target application, with total turnaround including baseline measurement, exposure, and final evaluation typically spanning one to four weeks. Because accelerated conditions compress years of service into weeks, correlation with real-world performance should be established for each product family.
What sample sizes and quantities are required?
Typical specimen dimensions are 50 mm × 100 mm or 45 mm × 50 mm for film and coating samples, with at least three replicates recommended for statistical validity. Unexposed reference specimens should be retained for comparison, and free-standing films, coated substrates, or finished sub-assemblies can generally all be accommodated.
What is the difference between xenon arc and UV fluorescent testing?
Xenon arc lamps reproduce the complete solar spectrum, including visible light that drives fading in many organic dyes and pigments, making them suitable for color-related evaluation. Fluorescent UV lamps emphasize the ultraviolet region, which accelerates polymer photooxidation, and are best used for material screening and UV durability comparison rather than full colorimetric assessment.