vary somewhat in response to the outdoor environment of a location. Two types of light offer potential decay to cultural heritage: ultraviolet (UV) light and visual light (light that can be perceived by the human eye). Although they can be affected simultaneously by removing light sources, reducing overall intensity, or increasing the distance between a light source and an object, best preventive practice treats these types of light separately due to their differences. Contaminants can come in many forms including naturally occurring chemical breakdowns in certain compounds, particulate pollutants, and accidental human contamination. Protecting collections from contaminants can be as simple as creating barriers to prevent abuse or as complicated as taking preventive actions to protect an object from its own chemical breakdown. Temperature Temperature acts primarily in conjunction with relative humidity, but it can trigger damage in its own right. Extreme high temperature can cause structural damage to some materials; paint may become brittle in excessive heat and some plastics may soften or melt in the heat. “High temperatures also accelerate chemical and biological processes,” which can lead to corrosion or embrittlement of material. Insects also thrive in warm environments, and so temperatures should be kept as “cool … as practicable in storage and display areas”. Any storage or display situation must take into consideration the temperature at which collection permanence can be optimized, and systems should be in place that aim to meet that standard, ideally in conjunction with efficient use of energy and funds. Different materials react to temperature in different ways. For example, ceramics are vulnerable to direct heat on a mechanical level, but many organic materials are at greater risk of undergoing phase transition if the temperature becomes excessively cold. One rule of thumb applies across the board: the rate of chemical reactions is dependent upon temperature in such a way that higher temperatures reduce the activation energy and hasten chemical degradation processes. Human comfort levels must also be considered. Storage areas can often get away with slightly lower temperatures than display areas since they are not accessed as often, and it is most likely that those who do enter the space will be prepared for the conditions. In galleries, however, viewers must feel comfortable enough with the temperature to spend time there, otherwise the collection will simply not be viewed and lose its purpose in being on display. Incorrect Relative Humidity Moisture has strong