When coatings age, various forms of degradation do not necessarily occur simultaneously. Some may first lose gloss or begin to chalk; others may undergo color shifts; still others might become brittle and crack within a very short period. Choosing between QUV-A, QUV-B, or Xenon arc testing in a laboratory setting essentially means selecting a specific combination of light and hygrothermal (moisture and heat) conditions to accelerate the manifestation of these changes.
While all three methods are classified as “accelerated aging” tests, the light applied to the materials differs significantly. Even if two test reports show the same number of exposure hours, the actual aging process experienced by the test panels may not be the same.
The primary difference between QUV-A and QUV-B lies in the lamps used.
“QUV” refers to the line of fluorescent UV accelerated weathering testers developed by Q-Lab. In the industry, tests using UVA-340 lamps are commonly referred to as “QUV-A,” while those using UVB-313 lamps are called “QUV-B.” While these terms are convenient for informal communication, formal test reports should clearly specify the equipment type, lamp model, and operating conditions.
- Tests colloquially known as “QUV-A” typically utilize UVA-340 lamps.
- Tests colloquially known as “QUV-B” typically utilize UVB-313 lamps.
Both types of lamps emit primarily in the ultraviolet (UV) spectrum, but they differ in their wavelength distribution and the severity of the stress they impose. Simply put, UVA-340 lamps more closely mimic the short-wave UV component of natural sunlight reaching the Earth’s surface, whereas UVB-313 lamps provide a more intense short-wave UV output, resulting in faster acceleration of the aging process.
Beyond the lamps, these tests incorporate cycles of light exposure, heating, and either condensation or water spray. Consequently, materials are subjected to a combination of UV-induced degradation, temperature fluctuations, and moisture ingress.
QUV-A: A Closer Approximation to Natural Outdoor UV Aging
The UVA-340 lamps used in QUV-A testing reach their peak spectral irradiance at approximately 340 nm. They are designed to simulate the short-wave UV portion of natural sunlight—the specific range most responsible for the degradation of polymeric materials.
Long-term exposure to this type of ultraviolet (UV) radiation can cause coatings to lose gloss, chalk, yellow, become brittle, crack, and exhibit reduced adhesion. Consequently, QUV-A testing is frequently used to compare the weather resistance of architectural coatings, industrial topcoats, plastics, waterproofing materials, and roofing products.
A key advantage of QUV-A is that its short-wave UV component closely approximates that of sunlight reaching the Earth’s surface. The gloss loss, chalking, and cracking observed in materials during QUV-A testing generally correlate well with the degradation phenomena seen in standard outdoor exposure.
However, because QUV-A focuses primarily on the UV spectrum—omitting the full range of visible and infrared light—it may not provide a complete picture, especially since certain color changes are significantly influenced by visible light.
QUV-B: Faster Degradation and More Severe Testing Conditions
QUV-B testing typically employs UVB-313 lamps, which feature a radiation peak near 313 nm.
This method delivers a higher intensity of short-wave UV radiation than QUV-A, including wavelengths that are rarely present in natural sunlight at the Earth’s surface. Under these conditions, materials tend to lose gloss, chalk, become brittle, and crack much more rapidly.
QUV-B is well-suited for the rapid screening of various formulations, comparing materials before and after raw-material substitutions, quality control across different production batches, and accelerated destructive testing of highly durable materials.
This “speed” comes with limitations. QUV-B may expose materials to higher levels of short-wave UV radiation than they would encounter in a typical outdoor environment. The resulting damage can be severe, and the sequence in which materials fail may differ from what occurs during natural exposure.
If a formulation cracks during QUV-B testing, it simply indicates poor performance under those specific test conditions. To accurately assess real-world outdoor durability, one must also consider data from QUV-A testing, xenon-arc testing, natural outdoor exposure, or existing project records.
Xenon-Arc: Incorporating Visible and Infrared Light
Xenon-arc testing utilizes a different light source approach than QUV systems. By employing appropriate optical filters, xenon-arc lamps can cover the ultraviolet, visible, and infrared spectra, providing a closer approximation of the full solar spectrum.
When color changes are influenced by visible light, xenon-arc lamps are generally better suited for evaluating lightfastness and fading. The fading of certain pigments, dyes, and organic materials is not caused solely by short-wave ultraviolet (UV) radiation; visible light also plays a role.
Xenon-arc lamps are frequently used to observe color changes, fading, yellowing, loss of gloss, surface cracking, and alterations in material strength. They are commonly employed to evaluate the lightfastness or weatherability of automotive coatings, coil coatings, vibrant topcoats, printing inks, textiles, and interior decorative materials.
Xenon-arc testing also requires the use of optical filters. “Daylight” filters are used to simulate outdoor sunlight, while “window glass” filters simulate indoor environments where sunlight has passed through glass. Changing the filter alters the short-wave UV radiation reaching the test specimens.
What are the key differences between these three types of tests?
QUV-A: Primarily simulates the short-wave UV component of sunlight reaching the Earth’s surface. It is a relatively mild test, often used to compare the loss of gloss, chalking, yellowing, and cracking of outdoor materials. It has limited sensitivity to color changes driven by visible light.
QUV-B: Features more intense short-wave UV radiation, typically resulting in faster aging; it is well-suited for formulation screening and quality control. However, these harsh conditions can sometimes cause excessive degradation, so test results should be cross-referenced with actual failure modes observed in the field.
Xenon-arc: Covers the ultraviolet, visible, and infrared spectra, making it ideal for evaluating color, fading, and overall weatherability. Results are influenced by the choice of filter, irradiance levels, temperature, and humidity cycles; therefore, these conditions must be considered when reviewing test reports.
From a technical perspective, QUV-A and QUV-B fall under “fluorescent UV aging,” which focuses on accelerating damage caused by UV radiation and moisture. Xenon-arc testing covers a broader spectrum, making it more effective for observing changes in color and appearance resulting from full-spectrum exposure.
Which method should you choose? It depends on what you intend to evaluate.
Focusing on loss of gloss, chalking, and cracking:
For outdoor industrial topcoats, architectural coatings, and plastic products, common issues include a reduction in gloss, chalking, yellowing, and cracking. These changes are closely related to short-wave ultraviolet (UV) radiation; QUV-A testing is generally effective at distinguishing the weathering resistance of different materials.
By incorporating condensation or water-spray cycles into the test, one can also observe whether the coating develops blisters, experiences a loss of adhesion, or exhibits other surface anomalies when exposed to moisture.
Since these condensation or water-spray cycles do not involve salts, pollutants, or the full range of conditions required for electrochemical corrosion, they cannot serve as a substitute for salt-spray or cyclic corrosion testing.
Rapid formulation screening
QUV-B testing is more severe, making it well-suited for rapid screening during the early stages of research and development.
However, as a product moves into the finalization, customer certification, or durability evaluation phases, relying solely on QUV-B is typically insufficient. It is also necessary to verify that the degradation modes observed in the test align with those encountered in the product’s actual end-use environment.
For instance, if the primary form of outdoor degradation is gradual loss of gloss and chalking, but the test panels undergo rapid brittle cracking under QUV-B, the test may be placing an excessive amount of stress via short-wave UV radiation.
Focusing on color and fading
Vibrant topcoats, automotive coatings, coil coatings, inks, and interior materials are particularly sensitive to color changes.
For such products, relying exclusively on short-wave UV may overlook fading caused by other parts of the visible light spectrum. Xenon-arc testing provides a more complete spectrum, making it better suited for evaluating color retention, fading, and lightfastness.
If a product is intended for indoor use, it is essential to ensure that the test is conducted using window-glass filters. Outdoor sunlight exposure and exposure to sunlight filtered through window glass represent distinct conditions and cannot be treated as interchangeable.
