Artcare - Auckland Art Gallery

example, if the illumination isfour times higher (200 lux)then the object should be displayedfor only three months ayear and stored in darkness forthe other nine months.Another possibility is to excludelight from the objects at alltimes when they are not beingviewed, for example with curtains,covers or time switches.Illumination for otherlight-sensitive objects on permanentdisplay should notexceed 200 lux.Although objects notaffected by light may be illuminatedat higher levels, it is not usually necessary toexceed 300 lux.Ultraviolet—as much ultraviolet radiation as possibleshould be removed (ideally all in excess of 50 microwattsper lumen) by passing the light before it reaches theworks through a material transparent to visible light butopaque to ultraviolet. Glass absorbs the most damagingwavelengths of ultraviolet (below 300–310 nanometers),but the radiation between 300–400 nanometers shouldalso be excluded to avoid damage.Recommended Light Levels forObjects on Permanent DisplayOil, tempera and acrylic paintings, undyedleather, lacquers; wood, horn, bone and ivory(where surface colour is important). . . . . . . . . . . . . . . . . . . . .200 luxWorks on paper, photographs, parchment,miniatures, textiles, costumes, plant fibres,fur, feathers, natural history specimens. . . . . . . . . . . . . . . . . . . . .50 luxThe Museum EnvironmentIllumination and Exposure Time—light intensity is New varieties of glass and acrylic sheeting willmeasured in units of lux. Exposure time is measured inlux hours. It is recommended that exposure time formuseum objects extremely sensitive to light, includingworks on paper, photographs and textiles, should notexceed 150,000 lux hours per year. This means that forobjects on display 365 days of the year the level of incidentlight should not exceed 50 lux, and light should beexcluded outside viewing hours (a maximum of 8 hoursper day). If it is considered necessary to illuminateobjects at more than 50 lux,absorb a great deal of the ultraviolet light but beware ofdeveloping a false sense of security when using theseproducts. Most allow some ultraviolet to get through aswell as the other damaging components of light (otherwavelengths, especially infrared). Although these productsare useful for delicate objects, light levels shouldstill be controlled within recommended levels.Plastic films (see also page 64) can be applied towindows to reduce ultraviolet levels as well as the othercomponents of light whichthen display time should beproduce glare and heat.reduced proportionately. ForManufacturers’ claims, however,should be tested with alight meter. These can be usefulfor homes, historic housesand other buildings wherecomplete blocking of naturallight is not appropriate.In the past most fluorescentlamps required ultravioletfilters, but new varietiesare available that emit muchlower levels of ultraviolet radiation(eg Philips 94). Ultravioletsleeves can be installedto reduce the ultraviolet toan acceptable level. It is alsoimportant that the ballasts offluorescent lights be mountedoutside a display case since they emit heat. Quartz halogenlamps emit high levels of ultraviolet but are availablewith an ultraviolet filter. The MR-16 variety havedichroic reflectors that scatter the light and reduce theheat. Tungsten incandescent lamps emit only a verysmall quantity of ultraviolet but generate a great deal ofheat which can be a problem in enclosed spaces or if thelight is too close to the artefacts. As the motor of fibreoptic lighting emits heat, it must be separated fromthe light.4