Assessing LED Lights for Visual Changes in Textile Colors
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Journal of the American Institute for Conservation ISSN: 0197-1360 (Print) 1945-2330 (Online) Journal homepage: http://www.tandfonline.com/loi/yjac20 Assessing LED Lights for Visual Changes in Textile Colors Courtney Anne Bolin & Mary W. Ballard To cite this article: Courtney Anne Bolin & Mary W. Ballard (2017) Assessing LED Lights for Visual Changes in Textile Colors, Journal of the American Institute for Conservation, 56:1, 3-14, DOI: 10.1080/01971360.2016.1275928 To link to this article: https://doi.org/10.1080/01971360.2016.1275928 Published online: 16 Feb 2017. Submit your article to this journal Article views: 172 View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjac20 ASSESSING LED LIGHTS FOR VISUAL CHANGES IN TEXTILE COLORS COURTNEY ANNE BOLIN AND MARY W. BALLARD North Carolina State University, Raleigh, NC, USA Museum Conservation Institute, Smithsonian Institution, Suitland, MD, USA Increasingly, museums are installing energy-saving light sources, such as LED (light emitting diode) lamps. LEDs represent an evolving technology; there are concerns about the effects of light spectra on artifacts, including textiles. Many LED models do not possess the same color rendering properties that observers are accustomed to, and it is important to understand the effects that spectra can play on dyed textiles. This research focuses on the visual effects of different light spectra, including those of LEDs, on textile colorants in order to gauge the range of color differ- ences produced. Nine early synthetic dyes and one commercial fading standard were utilized. This paper summar- izes our findings to date: that LED spectra with the same color temperature can render very different observable colors, especially with saturated colors. Saturated purples were found to be extremely hard to render accurately with LEDs. Other hues may also be compromised. Experimental work indicates that color temperature, illumi- nance level, and the commercial Color Rendering Index (CRI) are insufficient specifications for exhibitions LED light sources. An instrumental method for assessing LEDs before exhibition installation is suggested. KEYWORDS: Light emitting diode, LED, dyes, color rendering index, CRI, color quality scale, CQS, spectral power distribution, SPD, colorants, textiles .INTRODUCTION work by using inorganic semiconductors engineered for performance with phosphor materials. This Color and lighting of historic textiles is a critical factor creates an effect called electroluminescence, where in the visitor’s experience. Museum patrons want ade- light is emitted in response to an electrical current or quate light to perceive color well, while museums strong electric field. The first patent for applicable want to minimize light on artifacts to reduce actinic LED technology was issued in (Biard and damage. Traditional artificial lighting sources used in Pittman ) using gallium arsenide as the semicon- museums are incandescent, including halogen, and ductor. Over the last half century, semiconductors occasionally fluorescent. However, light emitting have become an important material used in many diode (LED) lighting is quickly gaining popularity as different industries, and the market demand is driving an energy-saving option because manufacturers are research in the electronics and lighting industry. now able to offer better quality assurance and color While gallium arsenide remains a popular semiconduc- uniformity. The spectral power distribution (SPD) of tor, indium gallium nitride is more common in current LEDs is, however, dissimilar to other artificial lighting cost-effective LEDs on the market. Indium gallium sources and can significantly alter the appearance of nitride’s emitted wavelength ranges from to artifacts. In order for museums to use these options nm depending on the material’s band gap (con- safely a better understanding of light spectra and their trolled by the ratio of GaN/InN) (Assessment ). effect on dye colorants is needed. To do this, spectrally As museums implement and install LEDs, it becomes sensitive dyes were observed and assessed under differ- increasingly important to understand how the spectra ent LED technologies. of these technologies affect the color rendering of his- The Energy Independence and Security Act of toric dyed textiles. introduced energy efficiency regulations for lighting The market for LEDs is expanding into fields where that have effectively banned (after ) the production color rendering is critical. The Department of Energy of incandescent lamps, excluding specialty bulbs (US (DOE) has funded the Solid-State Lighting Statutes ). With incandescent lighting obsolete, GATEWAY Demonstrations to showcase high- the lighting industry is producing innovative lighting performance LEDs in different applications, including options, including LEDs. LEDs are manufactured to museum gallery lighting. GATEWAY museum © American Institute for Conservation of Historic and Artistic Works DOI: ./.. Journal of the American Institute for Conservation , Vol. No. , – COURTNEY ANNE BOLIN AND MARY W. BALLARD demonstrations include projects with the Smithsonian warmer or cooler in color tone, meaning closer to American Art Museum, J. Paul Getty Museum, incandescent light or to daylight respectively. Finally, Jordan Schnitzer Museum of Art, and the Field can the SPD as described by its manufacturer be used Museum of Natural History. These reports focus on to predict color rendering? Nanometer by nanometer energy savings and feasibility of installing lamps in across the – nm visible spectrum, the LEDs detail, and examine appearance of artifacts displayed can be engineered to have specific levels of energy. under LEDs (Myer et al. ; Miller ; Miller et al. The SPD of LEDs can vary from other artificial lighting a, b; Perrin et al. ). However, they did not sources and could significantly alter the appearance of study the effects of LEDs on fidelity in color perception artifacts (Ohno, ). of textiles. The international color organization, Commis- sion Internationale de L’Eclairage (CIE), has released a .MATERIALS AND EXPERIMENTAL METHODS draft of terms and definitions for lighting with inorganic semiconductors that will later be developed into a standard . MATERIALS ’ (Commission Internationale de L Eclairage )anda Cotton and silk selected for dyeing were bleached report that examines the suitability of existing lighting desized cotton (style ) and silk broadcloth (style quality measures for interior LED lighting (Dikel et al., ) from Testfabrics, Inc. They possess similar fabric ’ ). With increasing interest in LEDs ability to render and weave structure, which reduces the possibility of color, there is a need to explore and collect information textural variation in the color readings (Table ; about the effects of LEDs used in museums to light galleries AATCC EP -). with historic dyed textiles. Dyes selected for the study included eight early syn- ’ The elements that make up an LED s semiconductor thetic dyes (Table ) from Dr. Helmut Schweppe’sselec- material determine the color of light emitted in a tion of popular dyes used for high value textiles like manner similar to neon lighting; there is a good deal tapestries, carpets, and silk fashions (Schweppe ). of variability between lamp models. The majority of These dyes were selected for their known poor light fast- LEDs use a semiconductor that emits a peak of blue- ness, for their particular hue and chroma, and for their green light and a phosphor that luminesces a broader levelness when dyed under laboratory conditions. Of band of orange-yellow, which together create a white particular interest were colorants with hues that fi light ( g. E). The white light produced in this reflected in two regions of the visible spectrum, such as manner by LEDs is not a true white light, meaning a orange-red or violet (fig. ). Colorants known for their white light made up of nearly equal quantities of all high chroma — intense brightness or saturation — that colors of light in the visible spectrum. While LED tech- might react differently to the small differences in the dis- nology does have the capacity to create a full spectrum tribution of radiant energy peaks, were chosen. light source, doing so increases the cost of producing the lamp and also sacrifices energy efficiency; LEDs are gaining interest for their energy-saving properties . SAMPLE PREPARATION and color rendering is not critical in many applications Cotton and silk fabrics were cut into samples that (Assessment ). Yet it is important to understand weighed approximately grams each and the the effects that spectra can have on the perception of weight, to four decimal places, was recorded. Each of dyed textiles, since many LED models may not the synthetic dyes was dissolved in deionized water at possess the same color rendering properties within the % by weight (e.g., gram of dyestuff per mL of tradition of incandescent lamps. deionized water). Each sample was separately dyed In this research three questions were asked: Does with the appropriate auxiliaries (Schweppe ) LED lighting change color rendering uniformly by using a : dye bath liquor ratio. affecting all colors equally or does it change color ren- dering by groups of color? Uniformly changing the . VISUAL EXAMINATION colors would affect the tonality but not their harmony. However, if different hues at different Ten unique SPDs with different attributes were chroma are not