PMG Section 1.5.2 Lighting Options

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Photographic Materials Conservation Catalog
Exhibition Guidelines for Photographic Materials

Date: July 2004
Contributors to WIKI version: Sarah Casto (LEDs)
Compiler: Stephanie Watkins, 1993-2004
Initiator: Douglas Severson, 1992-1993
Contributors (Alphabetical): Catherine Ackerman, Nancy Ash, Sarah Bertalan, Jean-Louis Bigourdan, Barbara N. Brown, Ed Buffaloe, Carol Crawford, Corinne Dune, Thomas M. Edmondson, Debra Evans, Julia Fenn, Betty Fiske, Gwenola Furic, Judy Greenfield, Doris Hamburg, Marc Harnly, Pamela Hatchfield, Cathy Henderson, Nancy Heugh, Ana Hofmann, Emily Klayman Jacobson, Martin Jürgens, Nora Kennedy, Daria Keynan, Lyn Koehnline, Barbara Lemmen, Holly Maxson, Constance McCabe, John McElhone, Cecile Mear, Jennifer Jae Mentzer, Jesse Munn, Rachel Mustalish, Douglas Nishimura, Leslie Paisley, Sylvie Pénichon, Hugh Phibbs, Dr. Boris Pretzel, Dr. Chandra Reedy, Nancy Reinhold, Andrew Robb, Grant Romer, Kimberly Schenck, Douglas Severson, Tracey Shields, Angela Thompson, Sarah Wagner, Clara von Waldthausen, Dr. Mike Ware, Stephanie Watkins, Dr. Paul Whitmore, Faith Zieske, Edward Zinn.

First edition copyright: 2004. The Photographic Materials Conservation Catalog is a publication of the Photographic Materials Group of the American Institute for Conservation of Historic and Artistic Works. The Photographic Materials Conservation Catalog is published as a convenience for the members of the Photographic Materials Group. Publication does not endorse nor recommend any treatments, methods, or techniques described herein.

Lighting Options for Exhibiting Photographic Material[edit | edit source]

Lighting equipment[edit | edit source]

The wavelength of infrared, visible, and ultraviolet radiation is measured in nanometers, nm or 10-9 m.

Natural lighting
Photographs must never be exposed to direct sunlight because of its high illuminance (12,000 fc or 129,120 Ix) and its rich ultraviolet content (Hendriks et al. 1991, 437). Indirect daylight must be filtered to remove the ultraviolet content and control brightness.

Artificial lighting
"Ultraviolet radiation content of lighting depends on the power and filament temperature of the lampl! (Knight 2001).

Incandescent tungsten lights

  • The color temperature of incandescent tungsten lights is typically within 2,700-3,100 K and will have an ultraviolet range of 65-75 μW /lm dependent on operating temperature of filament (Saunders 1989). Incandescent tungsten bulbs produce light strong in red­yellow appearance, but colored bulbs can be used to offset or balance this effect (Moor and Moor 1992, 196). The energy efficiency is less than other lighting sources for the brightness of the bulb.
  • Reilly (1986, 105) and Wilhelm (1993, 605) recommend tungsten incandescent lamps for the display of 19th century photographic prints. Some believe that tungsten lights give the best possible color rendition of monochrome photographic images. Reducing light intensity by using dimmers changes the color temperature of incandescent bulbs. Berrie has noticed that lowering wattage to reduce lux also increases inirared output (Phibbs 1997). Instead, the use of neutral density filters and metal screen mesh are recommended. Tungsten light bulbs generate heat through the burning of the filament, so fixtures and screens can get quite hot. Incandescent tungsten lights should not be set closer than 3 feet (l m) during exhibition (Raphael 1991, 13).
  • Moor and Moor (1992, 196) have written that while "tungsten lamps have the lowest ultraviolet output rating," they believe the lights "still should be filtered for ultraviolet and infrared." However, the amount of ultraviolet light from a tungsten lamp is extremely low. Fitting ultraviolet filters to these light sources may not be worth the money. Wilhelm (1993, 605) warns that "Ilford Ilfochrome (Cibachrome) print materials, Fuji FI-10, and 800 Instant Color films, the obsolete Agfachrome-Speed reversal print material (marketed 1983-1985), and the initial versions of Kodak PRIO Instant Prints™ introduced in 1976, have cyan dyes that fade more rapidly under tungsten illumination.

Quartz halogen lamps (tungsten filaments, quartz-iodine bulb)

  • The color temperature of quartz halogen lamps typically stays constant at 3100 K with an ultraviolet region around 120 μW /lm. Bulbs and sockets cost more than most other forms of lighting but last two times longer, use less electricity, and generate less heat and infrared radiation than do traditional tungsten bulbs (Wilhelm 1993, 605).
  • Quartz halogen lamps have significantly higher ultraviolet output than other incandescent lighting sources and should always be fitted with ultraviolet filters. "Even a glass-filtered quartz halogen lamp emits almost twice as much ultraviolet radiation within the 350-400 nm region as an unfiltered incandescent tungsten lamp. The greater ultraviolet output of glass-filtered quartz halogen lamps is probably of little consequence in terms of the fading rates of Ektacolor™, Fujicolor, Konica Color, Agfacolor, and most other current color print materials." (Wilhelm 1993, 605) Heat-resistant glass (also known as heat-absorbing glass) should be fitted to these lamps. *Quartz halogen lamps should not be set closer than 3 feet (1 m) during exhibit (Raphael 1991, 13).

Fluorescent lights (phosphor re-emission)

  • The color temperature typical of fluorescent lights is 3000-5000 K with an ultraviolet region within 40-150 μW /lm, although the amount of ultraviolet content varies with lamp type and style (Saunders 1989), power and filament temperature of the lamp (Knight 2001). Fluorescent lights have four times greater efficiency than tungsten sources with one-quarter the emission of heat and infrared radiation (Wilhelm 1993, 606). The average lifetime for tube-style fluorescent lights is 9000 hours.
  • Fluorescent illumination alone gives extremely poor color rendition of monochrome and color images due to non-continuous spectral output. Fluorescent lights should be filtered due to the ultraviolet output that is usually emitted at 313 and 365 nm and peaks at 405, 408, 436, 546, and 578 nm (Wilhelm 1993,606). Moor and Moor (1992,196), based on recommendations from Thomson, Hendriks, et al. state that fluorescent lights should be filtered "to below 75 μW /lm with filters and baffles." Fluorescent lights should not be set closer than 2 feet (610 cm) during exhibit (Raphael 1991, 13).

Fiber optic and light piping systems (can also be installed as a lighting fixture)

  • The color temperature for fiber optic and light piping systems will depend on the source lighting. Color temperature does not vary with reduction of the light level. Light piping and fiber optic systems transmit neither ultraviolet nor infrared components. High ultraviolet-emitting light sources can decrease the longevity of plastic piping. Filters over the light source may be desired in this circumstance (Sease 1993). Fiber optic and light piping are more cost efficient than other lighting types as one source will illuminate several areas. The longevity of lamps depends upon type.
  • Sease (1993) notes that fiber optic and light piping systems are flexible and cost effective for design cases. The lighting source can be set up exterior to cases. Optical lighting film can be rolled into tubes, curved, and cut to size although there is a slight intensity loss with length and number of bends. Optical lighting film does not need to be "refocused" if the lighting source needs replacement and can be used as a spotlight or as general illumination. The estimated life of film made of transparent acrylic or poly (carbonate) polymer is 10 years. The film is smooth on one side and grooved on the other, thereby acting as total internal reflection mirror (Sease 1993). Glass piping has a more focused light and is likely to be longer lasting than plastic.
  • Directional lighting is useful when exhibiting many types of photographic media that are light sensitive. A daguerreotype plate is easier to see when directional lighting is used in the same direction as the parallel polishing marks inherent in the process (see Reynaud 1989). Viewer-operated fiber optic mats (also known as "light on demand") can be used to illuminate wax paper negatives and transparencies from the reverse. (see also Lighting Techniques and Bowers 1999).

Light emitting diodes (LED)

  • Solid state lighting (SSL) light-emitting diode (LED) lamps are becoming widely adopted as an economical replacement of more traditional incandescent and fluorescent light sources in museums. LEDs utilize semiconducting elements rather than filaments or gas as an illumination source, and thus use less energy, generate less heat, and can last exponentially longer before replacement is required. The significantly higher up-front cost of LED lamps is offset by their longevity, low energy consumption, and reduced heating and cooling costs, all sources of savings which support energy sustainability and green initiatives (Druzik et al., 2012).
  • An LED is composed of a semiconductor that emits light of a certain wavelength or wavelengths and a lens or cover that is induced to fluoresce in a broader range while also diffusing the light. This results in a discontinuous spectrum, often with sharp, comparatively tall peaks in the blue region of the electromagnetic spectrum (usually 400-500 nm).
  • Generally, LEDs do not emit ultraviolet radiation. However, LEDs with violet chips emit a large peak in the near-UV (400-410 nm) and should be avoided.
  • Studies have shown that LEDs result in slower or similar fading rates compared to other lamps (Luo et al., 2016). Blue Wool Cards may not reliably indicate the true effects of LEDs due to their reflectance in the blue region of the spectrum.
  • LEDs have unique characteristics to consider when compared to other illumination sources for illumination of artwork:
    • Spectral power distribution (SPD) should be similar to that of a blackbody radiation source to maximize accurate color rendering and color temperature.
    • Color rendering index (CRI) greater than or equal to 90 on a scale of 100 is considered acceptable in museum settings for accurate rendering of colors.
    • Correlated color temperature (CCT) can be adjusted independently of the light source’s intensity. A range of 2700 K to 4000 K is typical CCT for most gallery settings.
    • KETRA LEDs allow adjustment of vibrancy as well as a deviation from the blackbody white light curve in CIE colorspace (called Duv), allowing greater control to enhance contrast and color of artworks.
    • LEDs exhibit vibration, a "flickering" caused as the electricity jumps the gap between diodes in the LED semiconductor to generate light. The flicker is too fast to detect with the human eye but can contribute to undesirable rendering of colors, interference bands in digital photographs, or visual discomfort for viewers. Some higher quality lamps are designed to minimize or eliminate this effect.

LED References

Glazing and filter materials[edit | edit source]

Considerations of glazing choices including ultraviolet inhibitors and filters

  • Light, even the visible range, is damaging to materials. Filtering the light source for ultraviolet radiation is desirable but does not eliminate the threat of light damage to photographic materials.
  • Wilhelm (1993, 612) suggests that "ultraviolet radiation can easily be reduced by using acrylic sheeting with an ultraviolet filter such as Lucite® SAR UF-3 or Plexiglas® UF-3" on individual framed photographs. TruVue's Optimum® Acrylic Glazing is also an option. Likewise, cases can be made with ultraviolet ­inhibiting glazing or an ultraviolet-inhibiting film can be applied to the exterior. Ultraviolet-inhibiting film can be applied directly onto window interiors or exteriors of frame glazing. Film can also reduce heat and glare and protect glazing from breakage and impact, some to the extent of a bomb blast. Lull (1999) believes that ultraviolet absorbing acrylic panels and laminated glass with a poly (vinyl butyral) ultraviolet-absorbing film are better options for reducing ultraviolet radiation than using films on windows. Window films are very thin; they break down faster than the glazing because of sun intensity, and within a few years they can start to separate from the glazing. Ultraviolet-inhibiting filters often come with a 10-year guarantee but seldom last past five years. Films should be considered as short-term applications because of the potential for separation. Predicting how long a filter will last is difficult because viability depends on the light level, length of exposure, and newness of the material. Long-term filtering effectiveness can be monitored by checking periodically with an ultraviolet light meter.
  • Ultraviolet films are available as covers for fluorescent bulbs and should be long enough to cover the ends, where much ultraviolet radiation is emitted (Glaser 1994, 2). Some light fixtures reduce ultraviolet radiation because of the materials used in manufacture of the bulb.
  • Wilhelm (1993, 577,607) has found that Ilford Ilfochromes/Cibachromes do not have an effective ultraviolet-absorbing emulsion overcoat so prints need to be protected from rapid fading by the use of ultraviolet-absorbing glazing such as, Plexiglas®UF-3. In addition, Kodak Dye Transfer® paper prints (dye imbibition process) do not have a UV-absorbing overcoat and can fade rapidly under high UV-conditions. Wilhelm (1993, 577) states that image fading of Ektacolor™/ Fujicolor/ Konica Color/ Agfacolor/ and most other current color print materials is caused primarily by visible light/ not by ultraviolet radiation. Ultraviolet filters do little to increase the life of these color materials/ largely because they are manufactured with an effective ultraviolet-absorbing emulsion overcoat.
  • Many modern photographs contain optical brighteners that fluoresce when excited by radiation within the 397-400 nm range. This includes, but is not exclusive to, energy emitted by tungsten light sources. The brighteners are fugitive and will fade and discolor.

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