LED TECHNOLOGY AND WHERE IT STANDS ON THE DILEMMA OF VISUAL PERCEPTION AND PRESERVATION

October 2022


Abstract

Museums are the experience of a space occurring by the relation between the one who sees and what is shown. How the objects are shown and displayed are important in terms of good visual performance. Mostly in museums, vulnerable objects, and monuments that need a conscious approach in terms of preservation are displayed.

What also defines the quality of this museum experience is lighting for people to see and objects to be seen. But the needed lighting condition might be different for the one who sees and what needs preservation.

How does lighting design stand in these needs of different actors of the museum? How does lighting affect visual performance and preservation? While the lighting manufacturers announce their products of  latest lighting technology, is it possible to provide both the perception and preservation in the museums?


Introduction

Light + Building, which is an event organized in Frankfurt, Germany to gather architects, interior architects, lighting designers, and more to share the latest trends and technology of the lighting industry, had hosted the “most photographed apple” in October 2022 on the stand of the lighting manufacturer DGA (Figure 1). The reason why the apple became so-called famous during the event was actually the size of the luminaire that illuminated it.  The luminaire was not stealing the attention from what was aimed to be displayed thanks to its small size. David Morgan, who shares his reviews about the lighting products on the Arc Magazine, was also saying in his review that the light output the luminaire produces is really useful and very convenient to be used in display areas such as jewelry displays and museums. ( Arc Magazine, 2021)

Figure 1: DGA luminaire displayed in L&B, October 2022

Nevertheless, the area where the apple was displayed was not a closed area and the heat of the luminaire was high enough to question the problem of the effect of the heat on the displayed object in the case of where the object is a monument that needs preservation. This question then led to other problems in addition to the heat that LEDs might cause on displayed objects.

Although manufacturers promise the latest LED technology with possible tiny products with a wide range of light distribution, variable CCT values, and high CRI, what are the damaging effects of LEDs in terms of lighting technology in the display areas like museums where the objects should be preserved?

On the basis of this problem, this paper will question the effects of light by looking at historical scientific findings, up-to-date researches, lighting design examples and by searching for the possibility of the balance between the perception of the one who is looking and the preservation of the object which is looked at since these two elements are the main notions of the experience in a museum.  It is aimed to find out the possibility of the LEDs for providing both visual performance and preservation.


Museums & Lighting

Museums are places where historical, cultural, scientific, and artistic objects are displayed. What defines the museum experience is the relationship between the object and the viewer. The quality of this experience is provided by lighting. Lighting in the museum has the role of allowing people to circulate through displaying areas as well as to show the object without disturbing the viewer.

To get the maximum efficiency for this experience, lighting should be designed in a way that the object has enough light which has the suitable color temperature, color rendering, and UGR value with necessary light distribution. What should not be ignored while this visual performance is wanted to be achieved is the effect of the lighting on the object. If we think about museums, there are different objects with different materials, colors, and textures that might require individual attention in terms of lighting and preservation.

Roman engineer and architect Vitruvius mentions a memory he witnessed about color and light in his sixth book of the series called “The Ten Books of Architecture” where he gives recommendations about architecture based on his experiences. According to his book, secretary Faberious had the walls of his house painted to vermillion color. One month later he recognized that the walls were darkened. As Vitruvius clarifies in the book, vermillion paint loses its strength and color by darkening when it is in interaction with sunlight  While the fact that Vitruvius had shared his experience centuries ago, philosophers could only start to think seriously about light and color at the end of the 17 century beginning with Isaac Newton’s optic studies (Druzik and Eshoj, 2007).

Although philosophers, artists, and color manufacturers were more concerned about color and light, and studies were started to understand the effect of the light, it could be said that South Kensington Museum in London might be one of the first examples of intervention made into architecture with the realization of the effects of the light. Glass skylights of the building were filtered to protect the Raphael cartoons in the museum in 1894.  Years later,  Lord Crawford expressed his ideas about this renovation in these words:

“One question which ought to be settled was how far there was any justification in using the results of scientific investigations to preserve the colors of museum specimens…Many years ago the Raphael cartoons at the South Kensington Museum had been placed in a fine gallery which was glazed with a nasty  lemon-colored glass, which gave one the feeling when entering the room of going into a tomb.” (Druzik and Eshoj, 2007)

The conflict between visual performance & experience and conservation had already begun at that time. On the other hand, the effect of the light was already known and was depicted even in paintings of painting galleries like “The Gallery of Cornelis Van Der Geest” (Figure 2) by Willem van Haecht in 1615. Curtains that were likely to be used for protection from the light can be seen right next to some of the paintings.

Figure 2: The Gallery of Cornelis Van Der Geest, Willem van Haecht, 1615

Back to the Basics

To be able to answer the question of how LED technology places itself in the conflict of preservation and perception today and understand the process of lighting technology, it is better to look at firstly, what was the reason behind using curtains with painting in galleries and filtering the glasses in the South Kensington Museum, the origin and oldest problems of light that is known.

In 1888, Russel and Abney published a report on the action of light on watercolors (Brommelle, 1964).  In this report, they compared the spectral energy distribution of sunlight, electric arc, and incandescent lamps. When the pigment absorbs radiation, it causes a rise in temperature and sometimes chemical reactions, according to them. They were also emphasizing the exposure time length by these words: “.. if the light is very feeble a bleachable color, no matter what length of exposure be given, will not fade. This is, however, not the case.” (Russel and Abney, 1888)

the intensity of the radiation x length of exposure = length of exposure x the intensity of the radiation

100 lm x 1 hour = 1 lm x 100 hours

They examined 46 pigments under different lights, conditions, differently colored filter glasses and concluded that blue and violet components in light were damaging the colors the most. Before Lord Crowford made his critique about the yellow light transmitted from the museums’ skylight, Abney was thinking “if a skylight was glazed with signal green glass and orange in right proportions, the colors (i.e. in paintings) appeared as in ordinary white light and the chemically active rays were cut off”.

Observations, depictions, and examinations about the effect of lighting have been made through the 19th century. Later on,  the first serious studies about the effect of light and museum lighting that counted as guidelines were made by Garry Thomson in 1978 for the National Gallery in London and published as a book called “The Museum Environment”

To compromise the conflict between perception and conservation, Thomson suggested 50 lux and 100 lux for displaying the light-sensitive materials and less sensitive materials respectively.  The findings were based on the lighting technology of his time when incandescent light sources were used. It is worth keeping in mind that this so-called guideline was telling that recommended lux levels were enough not to damage objects illuminated by incandescent and fluorescent lamps which contain UV. Thomson was actually already aware of the damage of UV and he was relating the damage to the wavelength. He says even a very small amount of UV from unfiltered daylight damages more than the complete visible spectrum. This of course was not meaning that visible light is harmless. Equal attention should be paid to both UV and visible radiation.

Radiation

There are scientific reasons behind the observations of the damages of visible and non-visible radiation of the whole spectrum that daylight includes from UV to IR. Photochemical reactions and radiant heating can result from exposure to light (CIE 157 2004) UV light with short wavelengths and high-energy photons can break down the chain of the molecules of the materials and cause physical and chemical changes. Photon energy may vary in different molecules, which is the reason why some objects can be damaged only by UV and others by visible radiation too. Photochemical actions are determined by irradiance, duration of exposure, spectral power distribution of incident radiation and action spectrum of the receiving material (Cuttle, Christopher, 2007)

“The radiant heating effect is the raising of surface temperature above ambient temperature due to the absorption of incident radiant flux.” (CIE 157 2004) IR radiation can cause the temperature to increase and it can cause the object to expand and moisture in the space and material of the object can be physically deformed. The reaction of every material to UV and IR may vary. Fading, yellowing, darkening, discoloring, twisting, bending, splintering, tearing, swelling, shriveling, shrinking, and dissolving (licht.de magazine)  can be counted as examples of the reaction of materials to light. 

Table 1: the wavelengths and energy of different types of light, Canadian Conservation Institute

Knowing the effects of UV and IR on materials it can be predicted how different artificial light sources might affect the materials by comparing the different wavelengths of the light sources. Short wavelengths with high energy and high wavelengths with high heat should be considered in the visible spectrum too. To decrease the damage - most probably the physical effects like loss in color and strength of the material -  they might cause, exposure to light should be controlled in both the amount of light and time. (Druzik and Michalski, 2012)

Table 2: Materials with different sensitivities

Table 3: UV proportions for various light sources, CIE 157 2004 Report

Daylight

Daylight plays an important role in terms of visual perception in the museum because of the fact that it can create glare in the display area. Although skylights and openings can be planned in a way to avoid direct sunlight, clear sky conditions should not also be ignored for glare. Even when the conditions are fulfilled to avoid glare, the ultraviolet content of daylight should not be ignored for the preservation of the objects.


Incandescent and Halogen Lamps

Incandescent and halogen lamps come with very good color rendering values which might be one of the essential features in museums for the correct perception of what is displayed. Since they are also located in the IR area of the spectrum, they can increase the temperature in display areas. As long as the light level is controlled like MR lamps which direct the light to the object and infrared radiation to the light fitting thanks to the dichroic reflectors (Figure 3), the damage of the infrared radiation can be decreased. (Saunders, David, 2020)

“Sunflowers wilt: Van Gogh's masterpiece is slowly turning brown as a result of exposure to LED lighting” was the title of the news of Independent Magazine in 2013. The news was basically becoming LEDs for yellows turning brown in Van Gogh’s works under the light exposure by referring to the scientist's discovery at the University of Antwerp. This could be huge life-changing information for all lighting industries especially when manufacturers claim to have the latest technology of LEDs in the market. Soraa, the LED manufacturer, was also concerned about this result and therefore started an investigation into the news. It turned out that what caused the degradation was not the LEDs but Xenon Lamps. The difference between these two types of light sources can not be missed out since Xenon Lamps contain a significant amount of UV compared to LEDs. LEDs in this way, were absolved from guilt thanks to the investigation for a while.

Figure 4: Comparison of different light sources, Soraa

Fluorescent Lamps

Thanks to their high efficacy, low cost, and ability to have different varieties of color temperatures, fluorescent lamps were preferred for illumination in museums in the 1940s. Phosphor in fluorescent lamps converts mercury vapor to light. The UV content of the lamp is defined by the efficiency of what mercury vapor emits. In addition to the high UV content they have, because of the control equipment they have to be installed with can create heat which should be prevented in exhibitions. (Thomson, Garry, 1978)


LEDs

LEDs are coming to the stage as the main character with their high efficacy but what is more important about LEDs for this paper is the little amount of UV they have and they result in low levels in the infrared area of the spectrum which can mean that the LED will create neither the photochemical reaction nor radiant heating on the object they illuminate. The spectrum might not cause these problems, but are LEDs still safe enough to use in display areas, and museums where the deterioration should be prevented?

Table 4: Efficacy of Different Light Sources (Druzik and Michalski, 2012)

Knowing the fact that shorter wavelengths with high energy levels are more deteriorated to cause damage and it is more accurate to classify LEDs by Correlated Color Temperature rather than blackbody color temperature since they do not generate light with heat (Druzik and Michalski, 2012), can we make a comparison between different light sources with different color temperatures referring to their wavelengths and come up with an acceptable color temperature for LEDs that are used in the museums? 

Table 5: Damage potential relative to CIE Standard Illuminant A (2856 K) (CIE 157 2004)

In the study on conservation aspects using LED technology for museum lighting (Piccablotto et al., 2015), scientists tested 5 LED sources differentiated by spectral emission and Correlated Color Temperature. Besides Cool white and Neutral white LEDs, 3 warm white LEDs were chosen since their spectrum was designed similarly to halogen lamps which were preferred because of their good color rendering feature. The Halogen lamp was also used as a reference source. In addition to the spectral data, they also measured the amount of UV and irradiance the light sources had. 

Figure 5: Relative Spectral Power Distribution (RSPD) of the selected light sources

(Piccablotto et al., 2015)

Table 6: Measurement results from laboratory characterization of the selected light sources

(Piccablotto et al., 2015)

As can be seen on the table which shows the measurement of different light sources, there is not a relevant correlation between CCT and UV amount. While cool white LEDs have higher CCT, it is measured to have less amount of UV than the LEDs with lower CCT. Having the comparison of these values, they made two tests as long-time exposure and short-time exposure to light to see the damage of the light on Blue Wool Standards and naturally dyed silk fabrics.

By observing the fading of the colors and comparing the light sources in terms of the CCT, they came up with a result that can question what the CIE metric claimed by relating CCT to the damage potential of the light sources and saying that LEDs with higher CCT cause more damage. At the end of their research, they found out that the color temperature of LEDs can not be related to high amounts of UV and damage potential as in traditional light sources.

As discussed in the paper so far, LEDs are efficient, can not be related to having more UV content and damage potential by comparing their CCTs, use electricity instead of additional heat to produce light, they seem to be convenient for museum lighting. What should not be avoided when using LEDs in exhibition areas is that, although LEDs are efficient at converting electrical energy to light, they still create heat during this process. Therefore, not the light but the light fixture itself will be the reason for the increasing heat in the display area - like the DGA luminaire which was given as an example at the beginning of the discussion. Raising temperature can cause expansion, and physical changes in the object but also this increase encourages chemical activity too (CIE 157 2004). Increasing heat in the LEDs also affects the lifespan of LEDs themselves as well as their effects on the objects. (Druzik and Michalski, 2012)

If we look at how LEDs are structured, we can see four main components: the LED chip, phosphor plate, substrate, and lens. The junction temperature is the temperature of the junction between the LED chip and substrate. The heat that occurred here should be passed away.  This whole structure of LED is located on a board called PCB, a printed circuit board where the heatsinks are attached to pass the heat away.

When it is wanted to decrease the distance between LEDs on PCB to create more compact designs for the luminaires, this causes the heat to increase. (Fisher, Alexander, 2022) (Also see Figure 6)

Figure 6: Temperature comparison between 0.5 mm spacing and 4 mm spacing

( Fisher Alexander, 2022)

Today: Raphael Court at the Victoria and Albert Museum

The first action was taken to protect the Raphael Cartoons in Victoria Albert Museum in 1894 by filtering the skylight. 128 years later, how are the paintings displayed in the museum?

Lighting Design studio StudioZNA worked on the lighting design of the renovation of the museum. The design team took the conversation into consideration as well as they worked on a flexible lighting design solution.

Before the renovation, the museum was lit by tungsten halogen lamps. There were unwanted reflections on the Cartoons which are exhibited in glazed frames and also not uniformly lit.

Figure 7: Stereoscopic albumen prints of South Kensington Museum, North Gallery (Gallery 94), south side showing four Raphael Cartoons, by J. Davis Burton, 1868, England

Figure 8: South Kensington Museum before renovation

Figure 9: South Kensington Museum after renovation

(Hufton + Crow)

For preservation reasons, they were working 50 lux levels for the paintings which the situation might be hard for one to able to look at the artwork and contrast of the light level between the display room and outside. They used LED lighting fixtures to illuminate the floor and provide a guide for circulation for visitors to look at the paintings. Besides general lighting, they increased the height of the light fixtures to avoid unwanted reflections (Figure 10) on the artwork and possible glares. By doing this they decreased the distraction and provided better visual performance for people. 

Figure 10: distracting reflections of the grazed glasses of the paintings

Conclusion

Looking at the lighting technology in history and today, lighting has had important effects on objects both physical and chemical which should not be avoided in display areas like museums. From daylight with the whole spectrum to the latest LED technology, lighting effects should not be disregarded. By the comparisons, it is found out that although LEDs do not have an important amount of  UV or IR to damage objects and do not produce heat as much as lighting sources before itself, it still produces heat.

While trying to achieve the best experience for visual performance for people to see better the displayed objects in the museums by providing all of the technical necessities like using the right light sources with the right angle directed to the displayed object, right CCT,  good CRI values, needed spectral power distribution, light output, controlled reflection, and refractions; preservation of the objects should also be considered by controlling the light and exposure by time. In the case of using the latest lighting technology LEDs, the possibility of increasing heat in the display area, especially where it is a closed space, should be prevented.

Lighting design should be addressed from the beginning of the design process with good analysis to understand the needs of the objects, and their sensibilities to light, UV amount, and heat. Attention should be paid individually since these sensibilities may vary because of different behaviors of different materials, colors, textures, and fabrics. Even planning the duration of illumination to which the object will be exposed can pave the way for the possibility to erase the dilemma of showing and seeing in the museums.


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