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topic 2401

Correlation between accelerated and natural weathering


Q. Does any one have any knowledge on the correlation between accelerated weathering testing & actual natural weathering testing for UV / Gloss retention / colour retention / chalking?

Example: 3000 hours accelerated weathering = 125 months of natural weathering. Is this close?


Ramoo Puru


A. Correlation between outdoor and artificial weathering devices is very material dependent. Factors that must be considered are light (both quantity and quality), moisture cycles, and temperature.

I don't know if 3000 hours is close to 125 months, but that sounds a bit unrealistic. What type of artificial device did you use? What was the cycle? What was the irradiance used? Commonly known cycles using a Xenon-arc source (the closest match to natural sunlight) require 1500 hours to achieve the same amount of radiant exposure as 12 months exposure in Florida. Degradation amounts may or may not be similar.

Matthew McGreer
corrosion testing equipment - Chicago, Illinois, USA


A. 125 months is about 90,000 hours. This is 30 times the 3000 hours of test time. This is too much of acceleration by any of the standards. A possible ratio is in the range of 8 to 12. This depends on the test conditions (temperature, humidity, irradiance level, condensation process, humidity, etc. The ratio would also vary according to the material that is being tested.

In the case of the Xenon arc test, the filter used would again be a determinant of the effects on the sample, while in the case of the QUV fluorescent tester, the median/peak irradiance wavelength of the lamps used would be a major factor in the effects on the sample.

It would be necessary to study the SPD of the lamps used also.

Varadarajan Seshamani
- Bangalore, Karnataka, India

(2006) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,
I'm a new member in these testing matters. How can I determine the duration of the accelerated weathering test according to SAE J1960 [link by ed. to spec at TechStreet]?

Siti Nazra Sulaiman
automotive - Malaysia


A. The duration of the testing is usually specified by the OEM or Tier 1 supplier that requires a certain dosage (usually expressed in kJ/m^2 @ 340 nm). You can use the following formula to determine the duration (in time) for that test:

Dosage = Irradiance X Time X Applicable conversion factor, (usually 3.6, which gets from joules to kilojoules and from seconds to hours, since a joule is defined as a watt-second).

More simply put:

kJ/m2 = W/m2 x 3.6 x Light Hours

You must also factor in time for dark cycles.

It is possible that you are wanting to know if there is some sort of "acceleration factor" with this test method. In other words, "How many hours of SAE J1960 equals one year of real-world exposure?" This is much more complicated, since the only way to truly answer this is to say that "it depends on the material tested." The only real way to determine it is to perform actual natural weathering tests in conjunction with the accelerated tests to determine the levels of correlation and acceleration for your particular type of material. At some point, you may be then able to extrapolate out to longer periods of time. But doing that carries certain risk.

Hope that helps.

Matthew McGreer
corrosion testing equipment - Chicago, Illinois, USA

February 4, 2009 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I'm also having hard time knowing the correlation between natural and accelerated weathering. If the Xenon-arc source requires 1500 hrs to achieve 12 months exposure in Florida, what was the intensity or amount of radiance in the place? In the Philippines, this relation would not be the same because of the difference in radiant intensity -- am I right? 12 months exposure in the Philippines might be lesser or greater than 1500 hrs in the xenon-arc source. Please help me find a correlation between natural and accelerated weathering especially for sealant test because currently it's my thesis. Please help me find the answer.

Jaymes Mendoza
- Manila, Philippines

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