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TECHNICAL BULLETINLU-8009QUV & Q-SUNA Comparison of Two Effective Approachesto Accelerated Weathering & Light Stability TestingThe Need For TestingLight, high temperature, and moisture, can cause damage to coatings, plastics, inks, and other organicmaterials. The resulting damage can be seen in many different types of polymerdegradation. These include changes in physical properties such as cracking, peeling, embrittlement,loss of tensile strength, etc; as well as visual properties such as gloss loss, fading, yellowing, colorfade and color change.For many manufacturers, it is crucial to formulate products that can withstand weathering and light exposure. Accelerated weathering and light stability testers are widely used for research and development,quality control and material certification. These testers provide fast and reproducible results.Two Different ApproachesIn recent years, low-cost and easy to use laboratory testers have been developed, including the QUV Accelerated Weathering Tester (ASTM G154) and the Q-SUN Xenon Test Chamber (ASTM G155).This paper will explore the ways in which these two testers differ, including emission spectra andmethod of moisture simulation. The inherent strengths and weaknesses of each tester will bediscussed, including purchase price and operating costs. Guidelines will be given for which tester isgenerally recommended for a particular material or application.The QUV tester is the world's most widelyused weathering tester. It is based on theconcept that, for durable materials, shortwave UV causes most weathering damage.Q-SUN Xenon Test Chambers reproduce the fullspectrum of sunlight, including ultraviolet, visiblelight and infrared.

Historical PerspectiveWhile it is clear that weatherability and lightstability are important for many products, the bestway to test is sometimes controversial. Variousmethods have been used over the years. Mostresearchers now use natural exposure testing, theQUV Weathering Tester, or a xenon arc chamber,such as the Q-SUN Xenon Test Chamber.Natural exposure testing has many advantages:it is realistic, inexpensive and easy to perform.However, many manufacturers do not have severalyears to wait and see if a “new and improved”product formulation is truly an improvement.The Q-SUN (xenon arc) and QUV (fluorescentUV) are the most commonly used acceleratedweathering testers. The two testers are basedon completely different approaches. The xenontest chamber reproduces the entire spectrum ofsunlight, including ultraviolet (UV), visible light,and infrared (IR). The xenon arc is essentially anattempt to simulate sunlight itself, from 295 nm 800 nm (see Figure 1 below).The sunlight spectrum consists of various wavelengths, which determine a material's mode ofdegradation in an outdoor environment.The QUV Accelerated Weathering Tester, on theother hand, does not attempt to reproduce sunlight,just the damaging effects of sunlight that can occurfrom 300 nm - 400 nm. It is based on the conceptthat, for durable materials exposed outdoors, shortwave UV causes the most weathering damage(Figure 1).3.00Q-Sun withDaylight - QFilter2Irradiance (W/m )2.502.001.501.000.500.00250SunlightQUV hich is the better way to test? There is no simpleanswer to this question. Depending on your application, either approach can be quite effective. Yourchoice of tester should depend on the product ormaterial you are testing, the end-use application, thedegradation mode with which you are concerned,and your budgetary restrictions.Wavelength (nm)Figure 1- Q-SUN and QUV Testersvs SunlightSunlight compared to the QUV and the Q-SUNtesters. The QUV weathering tester provides the bestavailable simulation of sunlight in the short-wave UVregion from 365 nm down to the solar cut-off. However, it is deficient in longer wavelengths. The Q-SUNchamber reproduces sunlight's full spectrum, whichis critical for testing many products that are sensitive to long-wave UV, visible light, and infrared.2To understand the differences between the Q-SUNand the QUV testers, it is necessary to first lookmore closely at why materials degrade.

Triple Threat:Light, Temperature, and MoistureMost weathering damage is caused by three factors:light, high temperature, and moisture. Any one ofthese factors may cause deterioration. Together,they often work synergistically to cause more damage than any one factor alone.Light. Spectral sensitivity varies from material tomaterial. For durable materials, like most coatingsand plastics, short-wave UV is the cause of mostpolymer degradation. However, for less durablematerials, such as some pigments and dyes, longerwave UV and even visible light can cause significantdamage.High Temperature. The destructive effects oflight exposure are typically accelerated whentemperature is increased. Although temperaturedoes not affect the primary photochemical reaction,it does affect secondary reactions involving the byproducts of the primary photon/electron collision. Alaboratory weathering test must provide accuratecontrol of temperature, and it usually should providea means to elevate the temperature to produceacceleration.Both sunlight through window glass and brightindoor lighting can degrade some materials.Moisture. Dew, rain, and high humidity are the maincauses of moisture damage. Our research showsthat objects stay wet outdoors for a surprisinglylong amount of time each day (8-12 hours daily, onaverage). Studies have shown that condensation,in the form of dew, is responsible for most outdoorwetness. Dew is more damaging than rain becauseit remains on the material for a long time, allowingsignificant moisture absorption.Of course, rain can also be very damaging tosome materials. Rain can cause thermal shock, aphenomenon that occurs, for example, when theheat that builds up in an automobile over the courseof a hot summer day is rapidly dissipated by asudden shower. Mechanical erosion is caused bythe scrubbing action of rain. This can also degradematerials such as wood coatings. Because rainwears away the surface, fresh material is continuallyexposed to the damaging effects of sunlight.Products exposed outdoors often remain wet 8-12hours each day.The major effect of humidity on indoor materialsis often the physical stress caused by the material trying to maintain moisture equilibrium with itssurroundings. The greater the range of humiditythe material is exposed to, the greater the overallstress. Although indoor products, such as textilesand inks, may only be exposed to moisture in theform of humidity, it can also be an important factor inthe degradation of outdoor materials. Outdoors, theambient relative humidity (RH) will affect the speedat which a wet material dries.The QUV and the Q-SUN testers each reproducelight, temperature, and moisture in different ways.Dew, not rain, is responsible for most of the damagecaused by outdoor wetness.3

QUV Weathering TesterSunlight Simulation. The QUV is designed toreproduce the damaging effects of sunlight ondurable materials using fluorescent UV lamps.These lamps are electrically similar to the commoncool white lamps used in general lighting, but aredesigned to produce mainly UV rather than visiblelight or infrared.The QUV Accelerated Weathering Tester usesfluorescent UV lamps to reproduce the damagingeffects of sunlight on durable materials.1.60Sunlight1.401.202Irradiance (W/m )There are different types of lamps with differentspectra. The type of lamp should best resemblethe light conditions found in your end use environment. UVA-340 lamps provide the best availablesimulation of sunlight in the critical short-wave UVregion. The spectral power distribution (SPD) ofthe UVA-340 matches sunlight very closely fromthe solar cut-off to about 360 nm (Figure 2). UV-Blamps (Figure 3) are also commonly used in theQUV. They typically cause faster degradation thanUV-A lamps, but their short wavelength output belowthe solar cut-off can cause unrealistic results formany 320340360380400420Wavelength (nm)Figure 2 - Noon Summer Sunlightvs UVA-340 IrradianceUVA-340 lamps provide the best available simulationof sunlight in the critical short-wave UV region.In just a few days or weeks, the QUV can reproducethe damage that occurs over months or yearsoutdoors.1.601.40Sunlight (ASTM G177)42Control of Irradiance. Control of irradiance (lightintensity) is necessary to achieve accurate andreproducible test results. Most QUV models areequipped with the SOLAR EYE Irradiance Controller.1 This precision light control system allowsthe user to choose the level of irradiance. With theSOLAR EYE controller's feedback-loop system,the irradiance is continuously and automaticallymonitored and precisely maintained. The Solar Eyeautomatically compensates for lamp aging or anyother variability by adjusting power to the lamps.Figure 4 shows how the irradiance control systemworks.Irradiance (W/m 320340360380400Wavelength (nm)Figure 3 - Sunlight, UVB-313, and FS-40UV-B lamps utilize short-wave UV for maximumacceleration and are most useful for testing verydurable materials, or for quality control.1 The SOLAR EYE Irradiance Controller is used in models QUV/se and QUV/spray. The SOLAR EYE controller allows better reproducibility and repeatability thanthe manual irradiance control procedure used for the model QUV/basic. The SOLAR EYE controller also reduces maintenance because the lamps do not have to berotated and replacement of lamps is less frequent.420

QUV SOLAR EYE IrradianceControllerWith the SOLAR EYE controller's automatic feedback loop system, the irradiance is continuouslymonitored and precisely maintained.How it WorksControllerPower Supply31sUV SnsorensorseUV SStep 1: The operator selects the desiredirradiance level. The level selected is the “setpoint.”24Step 2: During the UV cycle, built-in sensorsmeasure the light from each pair of lamps andtransmit this data to the controller.Base CabinetStep 3: Both the set point and the actualirradiance are continuously displayed for eachpair of lamps.Step 4: The controller compares the measuredirradiance to the set point.Figure 4 - QUV Weathering TesterIrradiance ControlThe QUV tester with the SOLAR EYE IrradianceController provides better lamp life and betterreproducibility and repeatability than testers withmanual irradiance control. Maintenance is simplifiedbecause lamps do not have to be rotated.Step 5: Then the controller instructs the powersupply to adjust the voltage to the lamps to maintain the set point.5