The role of an art museum is to acquire, conserve, research, and display works, providing the public with education, analytical opportunities, and entertainment. Museums and their exhibits create connections for the public to examine the past, present, and look towards the future and our progression as a species. These institutions chronical achievements and historical developments, which creates societal, aesthetic, and academic significance. As a result, the goal of museums is to not only offer their audience the greatest viewing experience, but to also conserve artifacts and artworks, which includes the overseeing of the conditions of their environment. Dependent on the artworks material, date of origin as well as institution, some of these conditions are subject to temperature control, moisture modulation, entry limitations, and lighting protocols.1
Throughout the years, there have been many studies in the way that colour temperature and lux interact with each other and the way in which objects are displayed. One of the most well recognised is the Kruithof curve. Created by its namesake, Dutch physicist Arie Andries Kruithof, the Kruithof curve was first publish in his 1941 paper entitled Tubular Luminescence Lamps for General Illumination. In his publication Kruithof gives an illustrated example of how different lux and kelvins interact with each other, depicting the best suitable combination in order to create a comfortable viewing experience for the audience. In his graph Kruithof details how these values react with each other, making objects appear too red or too blue in hue, as well as combinations that maintain a natural presentation (Figure 1).2
Figure 1: The Kruithof curve. The unshaded area is illustrated as the ‘pleasing’ combinations of CCT and lux. Source: The impact of illuminance and colour temperature on viewing fine art paintings under LED lighting, The Society of Light and Lighting, 2019.
While the Kruithof curve is still used as a tool to aid in optimal reproduction of colour, there have been many studies that show there is little evidence to support parts of the Kruithof curve. This is in part due to lighting technologies that were not used or may not have been available when he first published his findings. One of these more recent studies was performed in 2016 by Steve Fotios. In his case study entitled A Revised Kruithof Graph Based on Empirical Data, Fotios investigates modern shifts that give confirmation that certain correlating color temperature (CCT) and high lux levels do not need to be avoided.
‘Variation in CCT has a negligible effect on ratings of brightness and pleasantness. Low illuminances (less than approximately 300 lux) may be perceived as unpleasant; an illuminance of 500 lux is sufficient to provide a pleasant environment and a further increase in illuminance above 500 lux is of little benefit. Higher illuminances are perceived to be brighter and this effect appears to be stronger than for other relationships.’3
In his conclusion, Fotios maintains his findings that the only variable that should be avoided is low illumination and that CCT has no effect on the viewing experience. Similarly, a study published in 1990 by the Journal of the Illuminating Engineering Society stated that ‘subjective ratings of preference were influenced only by light level and not by colour temperature.’4
While different materials react differently, lighting is a large contributing factor to the overall deterioration of artworks. This is done by light’s ability to destroy and reorder the molecular bond within an object over time. Although there are many studies that share insights on lighting specifications, and recommendations there is no finite documentation on how museums choose a light source. This is in part due to many variables which include the institution, cost, sustainability, and the aesthetics that come on an item-by-item basis.5 Lighting is also important as it guides the audience through the institution, creating an experience from the moment they enter the space, to the moment they exit. Each room has the ability to tell its own story and create its own journey through the use of light work.
Recent research was also done to investigate whether LED, a lighting source manufactured well after the introduction of the Kruithof curve, had a similar or different effect on the viewing experience of the individual in terms of CCT and lux. During this study conducted in collaboration with the University of Leeds and Harbin Engineering University in 2015, twenty-four participants of different ages, genders, cultural and educational backgrounds viewed oil and gouache paintings. Their findings showed that lux had a much more sizeable impression on the visual experience and viewing comfort than CCT did. The information they gathered showed a disagreement with the Kruithof curve, as Fotios did, but they were also able to discover that in their study ‘lighting within the CCT range 2850–4000K and a moderate illuminance range of 200–800 lux is considered to be comfortable or pleasing for LED lighting of paintings in museums.’6
While CCT may not cause a direct effect on the viewer experience, museums strive to create a more realistic effect when displaying artworks. In order to do this many museums use the Colour Rendering Index (CRI) to create level lighting that will in turn react in a natural way to the colours in the artwork.7 CRI, first introduced in the 1960s, uses a metric system of zero to one-hundred in order to determine how lighting affects an object and how the colour is perceived. The goal is to find the truest colour of the object in question. This is calculated by how a light source reacts to eight specific colour swatches named R1 to R8 (Figure 2). In most cases, the higher the CRI, the more natural the colour to that being depicted within a piece of art. Light sources are tested with artworks and it is in this way that CRI is determined.
Figure 2: CRI test colour patches – R1 to R8. Source: Decoding Color Performance, Architectural Lighting, 2014.
CRI has been an active way to measure lighting effects, but it is not always an adequate estimation. An example of this is, again, with the use of LED lighting, created after the CRI. Julian Carey, director of marketing at Intematix, an LED manufacturer attested that the pastel colours represented in the CRI swatch test ‘are not representative of the world’. Due to this issue, secondary colour values have been used by many institution, that range between R9 and R14. This wider scope gives institutions that use LED a wider range of swatches to test from (Figure 3). The National Institute of Standards and Technology has also created a new scale of measurement named the Color Quality Scale (CQS) (Figure 4).
Figure 3: Supplemental test colour patches R9 to R14. Source: Decoding Color Performance, Architectural Lighting, 2014.
Figure 4: CQS colour samples VS1 to VS15. Source: Decoding Color Performance, Architectural Lighting, 2014.
‘The Color Rendering Index (CRI) has been shown to have deficiencies when applied to white light-emitting diode (LED) based sources. Further, evidence suggests that the restricted scope of the CRI unnecessarily penalizes some light sources with desirable color qualities. The [Color Quality Scale] CQS uses a larger set of reflective samples, all of high chroma, and combines the color differences of the samples with a root-mean square. Additionally, the CQS does not penalize light sources that cause increases in the chroma of object colors, but does penalize sources with smaller rendered color gamut areas. The scale of the CQS is converted to span zero to 100, and the uniform object space and chromatic adaptation transform used in the calculations are updated.8
CQS has not yet been labelled as a standard in the lighting industry, but it is currently being used widely and is ‘under consideration by CIE technical committee TC 1-91, which is tasked with recommending color quality metrics.’9
Museums are turning more towards the use of LED in order to decrease energy requirements as well as UV and IR damages. As these protective measures are taken, there should be little to no effect on the viewing experience. From here, as long as the preventative steps are taken, museums have the ability to employ CCT and create thematic lighting effects that will ensure a positive viewing experience for the audience without damaging precious works.
References
1 Rui Dang, Tan Huijiao, Review of lighting deterioration, lighting quality, and lighting energy saving for paintings in museums, Tianjin, 2021, 1.
2 Ian Ashdown, The Kruithof Curve: A Pleasing Solution, 2015, 1-2.
3 Steve Fotios, A Revised Kruith Graph Based on Empirical Data, 2016, 15.
4 Robert G. Davis & Dolores N. Ginthner, Correlated Color Temperature, Illuminance Level, and the Kruithof Curve, 1990, 33.
5 Carla Balocco and Guilia Volante, Lighting Design for Energy Sustainability, Information, and Perception. A Museums Environment as a Case Study, 2018, 2.
6 Zhai, QY, MR Luo, and XY Liu, The Impact of Illuminance and Colour Temperature on Viewing Fine Art Paintings under LED Lighting, 2014, 795-96, 808.
7 Mathew Pelowski, Andrea Graser, Eva Specker, Michael Forster, Josefine von Hinüber, Does Gallery Lighting Really Have an Impact on Appreciation of Art? An Ecologically Valid Study of Lighting Changes and the Assessment and Emotional Experience with Representational and Abstract Paintings, 2019, 3-4.
8 Wendy L. Davis, Yoshihiro Ohno, Optical Engineering: The Color Quality Scale.
9 Alice Liao, Decoding Color Performance, 2014, 24.