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A weatherometer is a laboratory device that uses high-powered light sources and water to simulate long-term outside exposure. Ultraviolet (UV) light, a wavelength of light from the sun not visible to the human eye, can cause long-term damage to paints, plastics and concrete finishes. Water, including rainwater and ocean saltwater, can attack finishes and degrade them. The weatherometer can create ultraviolet, indoor, or other light frequencies to test products in controlled conditions, and include water spray to add further environmental effects.
Test materials are formed into panels that can be placed inside the weatherometer. A reference or standard is often used, which may be an uncoated sample or a plastic without ultraviolet-protecting additives. This allows comparisons different coatings or treatments to the reference after long simulated exposures, and increasing test times can simulate years of outdoor exposure.
A high-intensity bulb provides light, with several types available to simulate different light sources. Carbon-arc bulbs can simulate sunlight and xenon can be used for indoor and outdoor light frequencies. Metal halide bulbs have been replacing carbon arc weatherometers since the late 20th century, because carbon arc bulbs require regular maintenance to replace the carbon electrodes in the bulb that wear out frequently.
Another effect of extended light exposure is a loss of color in a material, known as colorfastness. Colored pigments contain organic molecules that can be attacked by sunlight or artificial light from a weatherometer. Researchers can test the stability of various colors and additives used to protect them, under controlled laboratory conditions. Maintaining color stability is important because a paint or coating is used to protect metal, wood or concrete beneath; damage to the color can result in eventual damage to the underlying material.
Roofing materials can also be tested in a weatherometer, both for light stability and protection against thermal shock. When a hot roof is exposed to a rainstorm, the roofing shingles or covering will cool quickly and normally shrink or become smaller as they cool. This sudden change in temperature is called thermal shock, and can weaken the roof coverings. A laboratory test can simulate this effect to check various roof coatings for thermal stability and resistance to varying weather conditions.
Saltwater exposure can be very damaging to building and vehicle coatings, and new coatings must be tested for durability. Many weatherometers can simulate ocean salt spray to test coatings for marine applications or paints used on buildings near the water. Research has shown the effects of sunlight are often made worse by exposure to rain or salt water, making ongoing testing critical for these applications.
Weatherometer testing can also be used for fabrics, coated steel and plastics used in furniture and toys. Many hotels, businesses and homes use furniture, toys and athletic equipment outdoors, or place them outside permanently. Laboratory exposure can quickly test these products for durability and color retention in varying weather conditions, without the need to leave products outdoors for long periods.