Glossary of environmental monitoring

Museums establish, maintain and manage appropriate environmental conditions to preserve the collections in their care – this activity is usually referred to as ‘environmental monitoring and control’.

Environmental monitoring refers to the measurement and recording of environmental risks such as light, relative humidity, temperature and pollution. Environmental monitoring requires a knowledge of the factors to be monitored and the ways in which monitoring can be carried out and recorded.

Degrees centigrade for measuring temperature

Temperature is a measure of the motion of molecules in a material. When the temperature increases, molecules in an object move faster and spread out; the material then expands. When the temperature decreases, molecules slow down and come closer together; materials then contract. Temperature and temperature variations can directly effect the preservation of museum objects.

Relative humidity and temperature are measured using thermohygrographs and hygrometers.

Percentage for measuring relative humidity

Relative humidity describes how saturated the air is with water vapour. Relative humidity is expressed as a percentage at a certain temperature. “50% RH” means that the air being measured has 50% of the total amount of water vapour it could hold at a specific temperature. The temperature of the air determines how much moisture the air can hold so warmer air can hold more water vapour.

Relative humidity is important for museum collections because water plays a role in various chemical and physical forms of deterioration.

Relative humidity and temperature are measured using thermohygrographs and hygrometers.

Lux (lx) for measuring light

Light is another agent of deterioration that can cause damage to museum objects. Light causes fading, darkening, yellowing, embrittlement, stiffening, and a host of other chemical and physical changes.

Light is usually divided into two categories – visible light and UV light, which is invisible to the human eye. Light levels are referred to as the illumination level or illuminance, and are measured in lux, an expression of the amount of light flowing out from a source that reaches and falls on one square meter.

Light is measured using a light meter.

Taxonomic classification systems for identifying pests in museums

Pests may present a threat to museum collections. Recognising the most harmful species and signs of their presence is a first step to limiting damage.


Date created: 2016

Author: Collections Trust

Publisher: Collections Trust