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Specimen Orientation and Duration

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Specimens can be exposed at any orientation. The most common orientation is mounting at a fixed angle facing south. The following table lists the most common exposure angles used in weathering tests:

Angle* Typical Application
Most automotive specifications
34° Same as site latitude: generally the most accumulated radiant exposure in a typical year among the common exposure angles
45° Most popular exposure angle
90° Siding and other materials used at vertical orientation
14° - 34° - 54°
Maximizes radiant exposure with four angle changes per year with an overall increase over 34° of about 15%
* Measured from the horizontal, facing south

Specimens can also be mounted on follow the sun exposure racks. With follow-the-sun racks, the amount of solar radiation received by test samples can be increased by as much as 30%.

The duration of weathering is based on elapsed time (days, weeks, months, or years), or based on accumulated radiant exposure – either total (all wavelengths) or ultraviolet. Periodic inspections, measurements and/or returns are recommended.

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