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The exhibit design should be based on this range. The standard recommendation for illuminance of sensitive objects is 50-100 lux.Exposure can be controlled by limiting the light level, the time exposed, or a combination of the two factors. Both of these hypothetical exhibits may cause some light damage, but the museum lighting levels allow for a far longer exhibition before damage occurs:Īn artifact’s exposure to light can be predicted based on the light levels and the length of the exhibit. Understanding this formula, it is clear that exhibiting an object for 1 hour at 100,000 lux (direct sunlight) is equivalent to exhibiting the object for 200 hours at 50 lux (museum lighting). Light level (lux) x Time (hours) = Exposure (lux hours) The exposure of an artifact to light is a product of illumination level and time:
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Because it is a ratio, the total UV will increase as the light levels increase, even as the ratio remains constant. Ultraviolet is measured in microwatts per lumen (µW/lm), which describes the fraction of ultraviolet radiation in visible light. One footcandle (fc) is equivalent to approximately 11 lux. Visible light is measured in lux or footcandles. Light readings should be taken slightly in front of the actual object, carefully following the manufacturer’s directions. Less accurate light measurements can be taken with a smartphone app. Visible light and UV can be measured with a handheld lightmeter or datalogger.
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Many modern white papers also contain optical brighteners, which will make paper appear slightly whiter when UV is present, but this is not a significant difference. Human eyes cannot detect UV, so filtering UV will not affect the visual experience except for on certain very specific materials such as Day-Glo paints. It contains more energy and is therefore more damaging than visible light. Ultraviolet (UV) radiation is an invisible component of many light sources including sunlight, fluorescent lights, and traditional tungsten light bulbs. Objects that are not on exhibit should be kept in darkness. Facsimiles may also be used to avoid overexposure of the original artifact. When artifacts are placed on exhibition, steps should be taken to ensure that the light exposure is controlled, monitored, and recorded. Light damage can be mitigated by controlling the amount of total light exposure over time. Damage caused by light exposure is both cumulative and irreversible. Light damage is not only limited to fading: overexposure can also cause weakening, discoloration, yellowing and embrittlement. The amount of damage is determined by the intensity and type of light, the time of exposure, and the natural resistance of the object’s components.