Plastic fade resistance testing evaluates the ability of plastic materials, pigments and finished products to retain their original color when exposed to light, heat, moisture and other weathering factors. By using accelerated weathering technologies such as xenon arc and fluorescent UV lamps, accredited third-party laboratories can reproduce years of natural sunlight exposure within weeks or months. This article explains the technical principles, applicable standards, sample requirements, testing methods and evaluation criteria for plastic anti-fading (lightfastness) testing.
Technical Overview
Fade resistance, also referred to as lightfastness or colorfastness to light, describes the capacity of a plastic material to maintain its original color and appearance under the influence of ultraviolet radiation, visible light, heat, humidity and oxygen. When plastics are exposed to solar radiation, particularly the UV band between 290 nm and 400 nm, photochemical reactions occur that break polymer chains, degrade stabilizers and destroy chromophore structures in organic pigments and dyes. The visible consequences include color shift, yellowing, whitening, loss of gloss, chalking and surface cracking.
Plastic fade resistance testing accelerates these degradation mechanisms under controlled laboratory conditions by exposing specimens to artificial light sources that closely simulate the spectral power distribution of natural sunlight. After a defined exposure period, the degree of color change is quantified by instrumental color measurement (color difference, ΔE) or by visual comparison against calibrated gray scales. The principal international standards governing this field include the ISO 4892 series, ASTM G151, ASTM G154, ASTM G155, GB/T 16422 series, ISO 4582 and ISO 105-A02. Testing of this kind is essential for material qualification, product design, quality control and supplier comparison across industries such as automotive, construction, agriculture and consumer goods.
Testing Samples
Molded Plaques and Standard Specimens
For material-level evaluation, specimens are typically prepared by injection molding, compression molding or extrusion into flat plaques with a smooth, uniform surface. Common dimensions are 50 mm × 100 mm or 75 mm × 150 mm with a thickness of 1 mm to 3 mm. Flat, plane-parallel specimens ensure reproducible color measurement and uniform irradiation across the exposed face.
Finished Products and Components
Complete parts such as automotive trim panels, appliance housings, bottle caps, garden furniture, toys and cable sheaths can be exposed either as whole components or as representative sections cut from the product. Testing the actual finished article is preferred when surface texture, processing history and applied decorations (paint, printing, plating) may influence fading behavior.
Films, Sheets and Flexible Materials
Thin materials such as agricultural films, packaging films, geomembranes and coated fabrics are mounted on frames or backing cards so that the exposed surface remains flat and free of wrinkles during irradiation and condensation cycles.
Pigments, Masterbatches and Compounds
For colorant qualification, pigments and masterbatches are dispersed into a standard polymer carrier and pressed into plaques or drawn-down films. These specimens are then exposed alongside unexposed references to determine the intrinsic lightfastness grade of the colorant in a defined polymer system.
In general, a minimum of three replicate specimens is recommended for each exposure interval, together with at least one unexposed reference specimen retained in the dark for comparison purposes.
Testing Items
Depending on the product specification and end-use environment, plastic fade resistance testing may cover the following evaluation items:
- Instrumental color difference (ΔE*, ΔL*, Δa*, Δb*) between exposed and unexposed specimens, determined according to ASTM D2244 and CIE colorimetry as defined in ISO 11664
- Gray scale rating for color change (rating 1 to 5) in accordance with ISO 105-A02, where 5 means no visible change and 1 means severe change
- Lightfastness grade assessed against blue wool reference materials, typically rated from grade 1 (poor) to grade 8 (excellent) per ISO 105-B08 reference standards
- Yellowing index and whiteness index change, evaluated according to ASTM E313, which is particularly relevant for white and light-colored plastics
- Gloss retention measured with a glossmeter in accordance with ISO 2813 or ASTM D523
- Degree of chalking, assessed visually or by tape method with reference to ISO 4628-6 or ASTM D4214
- Visual defects such as cracking, blistering, crazing, staining and surface erosion, rated with pictorial standards or photographic references
- Retention of mechanical properties such as tensile strength and elongation at break after exposure, in accordance with ISO 527 or ASTM D638, as specified in ISO 4582
Testing Methods
Xenon Arc Lamp Exposure
Xenon arc weathering is the most widely used method for fade resistance evaluation because its filtered spectrum provides the closest match to full-spectrum terrestrial sunlight. Tests are performed according to ISO 4892-1 and ISO 4892-2, ASTM G155 or the equivalent GB/T 16422.2. Daylight filters simulate outdoor exposure, while window-glass filters simulate sunlight passing through window glass for interior applications. Typical operating conditions include an irradiance of 0.35 W/m² at 340 nm (or 0.51 W/m² at 420 nm for window-glass filters), a black panel or black standard temperature of 55 °C to 65 °C, a chamber temperature of about 38 °C to 50 °C, relative humidity around 50 %, and cyclic water spray such as 102 minutes of light followed by 18 minutes of light plus spray. Common test durations range from several hundred to several thousand hours, depending on the specification being applied.
Fluorescent UV Lamp Exposure
Fluorescent UV condensation testing emphasizes the short-wave UV portion of sunlight and is governed by ISO 4892-3, ASTM G154 or GB/T 16422.3. UVA-340 lamps reproduce the UV cut-on of natural daylight and are suitable for outdoor simulation; UVA-351 lamps simulate sunlight filtered through window glass for interior applications; UVB-313 lamps provide a severe screening test. The standard cycle consists of 8 hours of UV at 60 °C black panel temperature followed by 4 hours of condensation at 50 °C, allowing simultaneous assessment of photodegradation and moisture attack.
Carbon Arc Lamp Exposure
Carbon arc exposure, conducted under ISO 4892-4 or ASTM G153 with open-flame or enclosed carbon arc devices, is an older technique that is still referenced in certain legacy specifications, particularly in some Asian and American procurement documents. Its spectral distribution differs significantly from sunlight, so results should be interpreted with care when comparing with xenon arc data.
Natural Outdoor Weathering
For direct benchmarking, specimens can be exposed outdoors on racks facing the equator at a defined tilt angle, in accordance with ISO 877-1 and ISO 877-2, ASTM D1435 (GB/T 3681) or ASTM G7. Under-glass exposure (ISO 877 method) evaluates interior fading conditions. Although outdoor exposure requires months or years, it provides the reference data needed to establish correlations with accelerated laboratory tests.
Color Measurement and Rating Procedure
At each inspection interval, specimens are removed from the apparatus, conditioned in a standard atmosphere, and measured with a spectrophotometer using a defined geometry (typically D65 illuminant, 10° observer, and specified specular inclusion). The color difference between exposed and unexposed areas is calculated according to ASTM D2244, and, where required, converted to a gray scale rating per ISO 105-A02. ISO 4582 provides the general framework for reporting changes in color and appearance of plastics following exposure.
Applications
Plastic fade resistance testing supports material selection, product development and regulatory compliance across a broad range of industries:
- Automotive: interior trim, instrument panels, seat components, exterior body panels, bumpers, lamp housings and trim strips that must withstand years of sunlight exposure
- Building and construction: PVC window and door profiles, siding, roofing membranes, pipes and fittings, decking, wall panels and geomembranes
- Agriculture: greenhouse films, mulch films, irrigation pipes, tarpaulins and livestock housing components exposed to intense solar radiation
- Consumer goods and toys: colored housings, furniture, sporting goods and children's products, including colorfastness requirements referenced in EN 71 safety standards
- Electronics and appliances: TV and computer housings, remote controls, white goods panels and keyboards subject to indoor light and window-filtered daylight
- Packaging and printing: containers, labels and printed plastic films where brand color consistency is critical
- Colorant industry: qualification of pigments, dyes and masterbatches through standardized lightfastness grading in defined polymer systems
- Signage and advertising: outdoor displays, banners and illuminated signage requiring long-term color stability
FAQ
What is the typical duration of a plastic fade resistance test?
Test duration depends on the applicable specification and end-use requirement. Common xenon arc schedules range from 300 to 2,000 hours, while automotive and construction specifications may require 2,000 hours or more. Fluorescent UV tests are frequently specified in cycles of 500 to 1,000 hours. Testing is often performed at intermediate checkpoints (for example every 250 or 500 hours) so that the color change curve can be plotted over time.
What color difference value is considered acceptable?
Acceptance criteria are defined by each industry or product standard. As general guidance, many applications consider a color difference ΔE* of 3 or less as acceptable, corresponding to a gray scale rating of approximately 3 to 4. High-end automotive interior and architectural applications may demand ΔE* ≤ 2, while less critical products may tolerate larger shifts. The applicable limit should always be agreed between supplier and purchaser before testing begins.
Should I choose xenon arc or fluorescent UV testing?
Xenon arc testing is preferred when the full solar spectrum, including visible light, drives the fading mechanism, as with many organic pigments and dyed plastics. Fluorescent UV testing is preferred when short-wave UV and condensation moisture dominate the degradation mechanism, as with many coatings, PVC and polyolefin products. When a specification does not mandate a method, xenon arc exposure to ISO 4892-2 or ASTM G155 is generally the most defensible choice for fade resistance assessment.
Can accelerated test results be converted into years of outdoor service life?
There is no universal conversion factor between laboratory exposure hours and outdoor years, because real degradation depends on climate, latitude, season, orientation and pollution. A reliable correlation must be established experimentally by comparing accelerated results with natural weathering data for the specific material system. Accelerated testing is best used for relative ranking and specification compliance rather than absolute lifetime prediction.
What information is included in a test report?
A professional report from an accredited third-party laboratory typically identifies the test standard and machine type, exposure conditions (irradiance, filters, temperature, humidity, water spray cycles), total exposure duration, specimen description and conditioning, color measurement parameters, color difference values with gray scale ratings for each interval, photographic documentation of specimens before and after exposure, and a clear conclusion against the specified acceptance criteria.