cultural heritage items for exhibitions and loans. In general, lowering the temperature reduces the rate at which damaging chemical reactions occur within materials. For example, storing cellulose acetate film at 10 °C instead of 21 °C is estimated to increase its usable life by over 100 years. Controlling the relative humidity of air helps to reduce hydrolysis reactions and minimises cracking, distortion and other physical changes in hygroscopic materials. Changes in temperature will also bring about changes in relative humidity. Therefore, the conservation profession has placed great importance on controlling indoor environments. Temperature and humidity can be controlled through passive means (e.g. insulation, building design) or active means (air conditioning). Active controls typically require much higher energy use. Energy use increases with specificity - e.g. in will require more energy to maintain a quantity of air to a narrow temperature range (20-22 °C) than to a broad range (18-25 °C). In the past, conservation recommendations have often called for very tight, inflexible temperature and relative humidity set points. In other cases, conservators have recommended strict environmental conditions for buildings that could not reasonably be expected to achieve them, due to the quality of build, local environmental conditions (e.g. recommending temperate conditions for a building located in the tropics) or the financial circumstances of the organisation. This has been an area of particular debate for cultural heritage organisations who lend and borrow cultural items to each other - often, the lender will specify strict environmental conditions as part of the loan agreement, which may be very expensive for the borrowing organisation to achieve, or impossible. The energy costs associated with cold storage and digital storage are also gaining more attention. Cold storage is a very effective strategy to preserve at-risk collections such as cellulose nitrate and cellulose acetate film, which can deteriorate beyond use within decades at ambient conditions. Digital storage costs are rising for both born-digital cultural heritage (photographs, audiovisual, time-based media) and to store digital preservation and access copies of cultural heritage. Digital storage capacity is a major factor in the complexity of preserving digital heritage such as video games, social media, messaging services, and email. Other areas where energy use can be reduced within conservation and restoration include: Exhibition lighting - e.g. using lower-energy LED lighting systems and light sensors that switch lights on only when visitors are present; Installation of green energy capture systems in cultural organisations,