Method of the spectral addition for LED-based illumination of paintings
Method of the spectral addition for LED-based illumination of old masters oil on canvas paintings as exemplified in “Loth with his Daughters” by Arent de Gelder
Saint-Petersburg - Moscow 2016
opory Promelectrosvet”
Through “The Invitation to partnership and supplying of lighting fixtures for the Old Masters gallery of The Pushkin State Museum of Fine Arts”
Method of the spectral addition for LED-based illumination of Old Masters oil on canvas paintings as exemplified in “Loth with his Daughters” by Arent de Gelder
Lighting designer: Pavel Druzhinin pavel.a.druzhinin@gmail.com
Project manager: Tatjana Melukhina Laboratory engineer: Alexander Mezentsev Assistant: Evgenij Filipenko
Saint-Petersburg - Moscow 2016
Table of content
Table of content
Abstract
Identification of objectives
Common masterpiece description
Background
Current situation in-situ
The task
Theoretical aspects
Visual perception and visible light spectrums
Typical spectral distribution curves
Spectral additions method
LEDs and painting conservation issues
Modeling
Visual modeling
Mockup in the “Light Point” laboratory
Variation of spectral additions and combining results
Criteria for choosing the spectral addition
Experimental illumination of the Arent de Gelder’s painting in The Pushkin State Museum of Fine Arts
This work is aimed to describe the method of illumination of art paintings using LEDs. This method is based on visual perception and suitable for application in any conventional gallery space.
Main features of the method are:
- using combination of high color rendition LED as base light source and additional filtered LED light, - mixing the light of two or more sources on the surface of a painting, - spectral addition are based on visual perception of museum scientific staff and curators, - considering damage potential and measuring lighting parameters (R, R, CCT, CQS, E, a14 e E).
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Identification of objectives
Masterpiece description
The painting “Loth with his Daughters” by Arent (Aert) de Gelder (oil on canvas, 142x123 cm) is exhibited in room N10 of The Pushkin State Museum of Fine Arts in Moscow. It was painted in early 1680s (between 1680-1683, source: Moltke & Sumowski). Arent de Gelder was one of the last Rembrand’s apprentices.
The painting’s theme is a bible story about Loth and his daughters: “Lot's daughters make their father drunk” (Genesis 19:33). Current condition of the painting is poor.
Background
The current lighting system in room N10 of The Puskin Museum is using old types of halogen track-luminaires with MR-16 lamp without any special accessories. At this point the system is far from being the most energy-effective and flexible for museum. Modern light sources like special museum LED can be used to design unique lighting systems for any exhibition
Old masters paintings, in particular before restoration, have dark yellow lacquer on their surfaces, so that they appear ocher-colored. Conventional light sources, e.g. halogen lamps, due to their spectral distribution, increase this perception by suppressing blue and green hues. LED light sources, on the other hand, allow to adjust the spectrum to counterbalance the red-yellow hues by enhancing the blue-green ones, resulting in better color rendition and preservation.
Current situation in-situ
Lighting fixtures are mounted on a 3-phase lighting track on a 5.7 meter high ceiling.
Top: General view of room N10 and the painting “Loth with his daughters” (source: Google art project), Bottom: General view of the room N10 and frontal view of the painting (photo: Pavel Druzhinin)
The task
Given the current lighting situation, we can define the following objectives.
1. Develop a specific artwork lighting techniques for the Old Masters paintings in The Pushkin Museum of Fine Arts, using contemporary LED lighting fixtures.
2. Test the installation and document the results.
3. Ensure an adequate and comfortable perception of the paintings with regard to the permissible exposure limits (illuminance and irradiance).
4. Incorporate the opinions of the curators and the scientific staff of the Museum into the lighting solution.
Theoretical aspects
Visual perception and visible light spectrums
Light sources with different spectral distribution (mostly, we are talking about color temperature) cause differences in visual perception. Here we are considering a human eye color adaptation as demonstrated by the following painting.
Source, spectral distribution:
Source type A
Materials from Alejandro Ribes Cortes’s work “Analyse multispectrale et reconstruction de la reflectance spectrale de tableaux de maitre” 2003, Paris. (Tungsten lamp) (Daylight at 6500K)
Standard source D50 (Daylight at 5000K)
Examples of software-modeled approximate appearance.
Using the contemporary light sources like LEDs, combined with color filters or multispectral sources allows to correct or completely change the visual perception of a painting. Now it is possible to show it in its historical context or exhibition environment, hide the old yellow lacquer effect, uncover hidden details.
a m hite
Cool white with red area accentuation
Neutral with green area attenuation
Neutral with red area accentuation
Neutral with green area accentuation
Typical spectral distribution curves
Wavelenght, nm
Wavelenght, nm
Wavelenght, nm
Spectral additions method
Applying spectral addition is about finding the optimal light spectrum that results in the most suitable appearance of apainting, with compensated yellow lacquer, more natural colors of items like fabrics and characters. It can only be applied to paintings in good condition, with enough pigments to reflect light.
The method involves mixing of the basis light — white, CCT 2800-3000K, good color rendition Ra>95, low damage factor with small addition with different spectrum, that slightly accentuates selected hues. In case of old masters paintings, this addition could be green-blue to achieve the “yellow laquer compensation”.
One of the characteristics of LED light sources is a significant and dangerous peak in 440-450 nm area, that would cause most photochemical damage to a painting.
Because of that, the basis light source was chosen between 2800-3000K source. And another reason — this would also add to the “classic” ambience in the room.
Lighting fixture with the “basis” light source forms a flood light beam, that illuminates a painting and the surroundings. Another lighting fixture with “additional” light source forms a smaller beam that is directed only at the area inside the frame of the painting.
LED light sources +
Halogen
Relative spectral distribution curve for human eye sensivity λ (fits with normalizing curve of luxmeter)
Relative spectral power distribution of LED with CCT 4000K
Relative spectral distribution of damage factor λ
It is necessary to name some issues, that are very important for painting conservation it terms of LED-lightng:
1. Assume dangerous blue peak in the 440-450nm area that is slightly detectable by a luxmeter.
2. Applying standard recommended ISO lux-levels is not permitted.
3. Light sources with lower CCT (2700-3000K) cause less damage than light sources with higher CCT.
4. UV- and IR-filters are prefered.
Modeling
Visual modeling
“Classical” illumination using one light source with CCT 3000K (top) and the combination of two light sources with CCT 3000K and 4000K (bottom). The position of lighting rack in the model if modeled after hat of the room Nr. 10 of The Pushkin Museum of Fine Arts.
Modeling and visualizations are created using 3D Max software.
CCT 2800K, Ra=91 1340 lm (max) with dimming frame optic system color filters
Additional spectrum and filters
A. Initial spectral power distribution (2800K, Ra 91), 1. A+yellow-green filter, 2. A+green filter, 3. A+blue filter, 4. A+blue+yellow-green filters.
Variations of spectral additions and combining results
Basis spectrum (3000K)
Spectral addition (2800K+filters)
Result of combination
Basis spectrum (3000K)
Result of combination
Spectral addition (2800K+filter)
Criteria of choosing the spectral addition
The choice of the spectral addition and its proportion to the basis light source is at the core of this method. It is necessary to define the criteria of choosing this spectral addition and complete spectrum for painting illumination.
1. The (average) reflectance spectral distribution of the painting. It is necessary to determinate hues that should be accentuated. For marine and landscapes - blue hues, for genre painting - it is likely green hues. It generally depends on the specifics of the painting and the curator’s point of view.
2. Historical context. It is necessary to recreate or preserve lighting atmosphere of a painting and its surrounding, when and where it was created. This, certainly, should be decided together with exhibition curator and museum’s scientific staff.
3. The ratio between the basis and the additional lighting should not highly reduce color rendition, and illuminance (irradance) levels must be limited. This point is to be researched.
Experimental illumination of the Arent de Gelder’s painting in The Pushkin State Museum of Fine Arts
Basis
15° round symmetrical beam with smooth edge
Lighting spot setup
Additional projection frame with slightly smoothed edge
lighting spot
To prevent multi-colored chaotic appearance of the exhibition space, it is necessary to determine one common type of basis lighting source for whole exhibition space (room). Here it was Xicato Artist based lighting fixture with 15° reflector, 3000K. It was installed on a track instead of old lighting fixtures, nearly in the front of the painting (the lighting track is slightly moved to the left from the center of the painting). Right next to the basis lighting fixture a projection lighting fixture (Sylumis Syclop, 2800K) was installed, that produced additional lighting. The projection was adjusted to fill only the area inside the painting’s frame with additional light, with smooth edges. Using dimmers on each lighting fixtures, the most distinct picture was achieved.
Combined
Combining spectrums results
Basis (3000K)
Combining result
Notice: blueish smooth spot on the painting - is a reflection of a window in front of it..
When the method of spectral addition was used, there appear some issues in details: Greenish pigments in clothes and its texture are reading more clearly (1, 2); Skin tone nuances became more readable (3); Hidden darken details become more apparent (5, 6, 7); But the lacquer became more “dusty”, and darker fields become lighter and the painting’s damages become more obvious (4).
Notice: blueish smooth spot on the painting - is a reflection of a window in front of it..
Conclusion
The method of spectral addition for Old Masters paintings improves the appearance of the painting, making it more spectacular, improves the perception of colors and correlates it with its historical context, preserving common lighting atmosphere in the room and picking the right individual additional spectrum for each masterpiece .
Experience with the painting “Loth with his Daughters” by Arent de Gelder in “The Pushkin State Museum of Fine Arts” shows that this method is able to not only enhance the features of a painting, but also its defects — damages, crackles and so on.
For this reason, the spectral addition for each painting must be selected very carefully, considering lot of parameters, such as color palette, painting condition and curator’s mention.
The method of spectral addition is not applicable for some paintings and should be used very carefully, with the assistance of scientific staff, colorimetric and climatologists.
