cumulative and irreversible. Conservation science has helped establish 50 Lux as the benchmark level of light intensity that allows the human eye to operate within the full range the visible light spectrum. While this is a baseline for many museums, adjustments are often needed for based on specific situations. Conservation science has informed the industry on the levels of light sensitivity of common materials used in material culture and the length of time permissible before deterioration is likely to occur. Control strategies must be considered on an item by item basis. Light, ultraviolet, and thermometers for infrared radiation are some of the tools used to detect when levels fall outside of an acceptable range. Lightning Lightning strikes are the primary natural cause of damage to architectural heritage because ancient buildings generally use timber with high oil content, such as pine. Lightning strikes can cause the timber in the building to catch fire by the heat of the lightning arc. Lightning can also split wood and cause damage to the building structure.The lightning current will generate heat after passing through the timber and generate gas inside, and the impact force formed by the instantaneous expansion of the gas will knock the wood out of damage pits or cracks. Stone decorations on ancient buildings may also suffer physical damage from lightning. Incorrect relative humidity Relative humidity (RH) is the measure of the humidity, or the water vapor content, in relation to the atmosphere and ranges from damp to dry. Material properties determine the affect that different levels of RH can have on any particular item. Organic materials like wood, paper, and leather, as well as some inorganic material like metals are susceptible to damage from incorrect RH. Damage ranges from physical changes like cracking and warping of organic materials to chemical reactions like corrosion of metals. Temperature has a direct effect on relative humidity: as warm air cools, relative humidity increases and as cool air warms up, relative humidity falls. Dampness can cause the growth of mold which has its own damaging properties. Research in the field has determined the various ranges and fluctuations of incorrect humidity, the sensitivity of various objects to each one, and has helped establish guidelines for proper environmental conditions specific to the objects in question. Incorrect temperature Material properties directly determine the appropriate temperature needed to preserve that item. Incorrect temperatures, whether too high, too low, or