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LED Usage in Museums and Art Galleries

  
  
  

by: Raghuram Petluri; Roger Sexton

Introduction

LEDs provide an energy and maintenance saving alternative to halogen for museum lighting. Previously high Color Temperature single phosphor corrected white LEDs had shortcomings with gaps in the spectrum affecting accurate color discrimination and high outputs / spikes in the blue area affecting color degradation. Recent improvements in LED technology make their usage ideal in all areas, light sensitive and insensitive alike. This paper takes the Artist Series module from Xicato to quantify this statement.

Background: LED usage in museums and art galleries

Compared with tungsten halogen, LEDs provide energy and maintenance savings. LED efficacies and useful lifetimes are higher than that of halogen lamps, eg for the Xicato Artist Series modules up to 40lm/W (depending on drive current) and 50k hours (to an expected 15% depreciation) respectively. Life is important in terms of maintenance costs, but also ruggedness is critical bearing in mind the effects of continuous luminaire repositioning as exhibitions are changed. Dependable reliability is needed for peace of mind against the tarnishing of an establishment’s image that would follow failures -more of a consideration than normal if the failure is contributing not just to an ambience but to the perception of a work of art.

Additional advantages compared with halogen lamps include the lack of UV which can cause deterioration of some materials, and IR, which causes heating (which will further effect material deterioration).

The above advantages of LEDs have already led to their wide uptake in non-light sensitive areas, and for the first time also in display areas. Questions have been asked about their usage in the latter areas owing to Spectral Power Distribution (SPD) related issues1,2. These questions concern impairment of human color discrimination and impairment of light sensitive materials. These issues are fundamental and will be dealt with first.

Fundamental issues: suitability of LEDs for museum lighting in terms of color discrimination and impairment of light sensitive materials

LED sources have previously been evaluated for their suitability in museum lighting by Mie ISHII et al in 20071. Tests for effect on color degradation of different natural dyes and different blue scale standards (the index of light color fastness for dyed fabrics) were carried out with different LED technologies and an accumulated exposure time of 150000lx.hr (a CIE standard for light fugitive materials of medium responsivity3 ). The main findings were that particularly single phosphor LEDs of a high CCT (over 4000K), especially if there are abrupt peaks in the spectrum around 400 – 500nm, have a greater effect on the fading of yellow dyes or blue scale grade 1 and 2 standards than that of museum fluorescent lamps (NU).

Another issue highlighted by Kronkright1 involves the effect of a non-continuous spectrum on an accurate perception of a work of art.

The above observations and cautions were relevant with the phosphor corrected LEDs of the time. Advances in the light quality of LEDs and LED modules, particularly LED modules with a separated and tuned phosphor, not only overcome these shortcomings but present a solution on a par with halogen lamps. Specification points to be certain of in this respect include: 

  • A high CRI across all 15 CIE Test Colors (CIE 13.3-1995) to ensure accurate perception of exhibits  
  • Limited output between 400-500nm. From the color perspective, the blue portion of the spectrum (which is abundant in sun, moon and starlight) is needed for the proper functioning of human eye, so there should be some light in these wavelengths, but certainly no higher than halogen.  
  • In general a SPD that follows as closely as possible the Black Body Locus ( BBL) with gradual changes and not spikes   

In figures 1 to 3 the Artist Series module from Xicato, which uses their patent pending “Corrected Cold Phosphor Technology”, is compared with traditional light sources in terms of CRI and halogen and standard phosphor corrected LEDs in terms of a SPD analysis, to demonstrate how the above weaknesses are solved. Figure 4 shows an application demonstration of the Artist Series module alongside tungsten halogen.  

  

 Figure 1describe the image

 Xicatos Artist Series module Color Rendering properties compared with traditional lamp types. Test Color Samples 1 to 15 are detailed, from CIE 13.3-1995. Measurements by University College London 

Notes:

  • High rendering properties across the visible spectrum allows fine color discernment of museum or gallery exhibits, bettering typical compact metal halide or compact fluorescent sources and on a par with halogen sources

  Figure 2 describe the image

Comparison of SPD for Xicatos Artist Series module (3000K) with halogen and Cool White pc LED. Outputs normalised to 700lm – the output of the Xicatos Artist Series module at 700mA operation 

Notes:

  • Below 400nm
    • Halogen has nearly 4 times more light than Xicato Artist module
  • In 400-450nm region
    • Xicato’s Artist Series module has less light than Halogen (87mW compared to 110mW)
    • Cool white pc LED has twice the amount of light of Halogen (236mW)
  • Change in intensity from the adjacent spectral band is
    • Gradual with the Halogen lamp
    • Abrupt with the Cool White pc LED
    • Gradual change close to Halogen lamp with the Xicato’s Artist Series module

 

Figure 3Museum Lighting Chart3 resized 600

Comparison of SPD for Xicatos Artist Series module (3000K) with halogen and Warm White pc LED. Outputs normalised to 700lm – the output of the Xicatos Artist Series module at 700mA operation 

Notes:

  • Below 400nm
    • Halogen has nearly 4 times more light than Xicato Artist Series module
  • In 400-450nm region
    • Xicato’s Artist Series module has less light than Halogen (87mW compared to 110mW)
    • Warm white pc LED has less light than Halogen but more than Xicato’s Artist Series module (91mW)
  • Change in intensity from the adjacent spectral band is
    • Gradual with the Halogen lamp
    • Abrupt with the Warm White pc LED
    • Gradual change close to Halogen lamp with the Xicato’s Artist Series module 

 

Figure 4Museum Lighting Chart4 resized 600

An application demonstration of Xicatos Artist Series module alongside tungsten halogen (thanks to Mike Stoane Lighting)

 

LED usage for museum and gallery lighting: the wider picture

Having dealt with the above fundamentals, there are a number of other reasons why LED solutions such as the Xicato’s Artist Series module are ideal for museum and gallery lighting. 

  • Changing exhibitions mean that dimming is normally essential to create the right viewing conditions each time – this is achievable without color shift.  
  • Regarding overall aesthetics, the Xicato’s Artist Series’ 2700K option is often needed to create a comfortable environment at low light levels (Kruithof’s Law on emotional responses to light levels / correlated colour temperatures – see Figure 5).  

 Figure 5Museum Lighting Chart5 resized 600

The Kruithof curve 

  • Stability of color point through life is essential for maintenance of a design. With Xicato’s Artist Series module this will not deviate beyond 2 Standard Deviation Colour Matching ellipses (SDCM) of the original color point. (When traditional lamp replacements are made, even with halogen if it involves a different manufacturer, there can be marked differences in color appearance).  
  • As accent lighting is normally track mounted in this segment, miniaturisation can contribute towards overall aesthetics. Often the architecture itself is grand or dramatic and the less obstruction from building services hardware the better.  
  • As with halogen lamps different beam angles are possible. Beam control for the Xicato Spot modules can be achieved by changing the reflectors, something which can be done on site. As the source is a uniform lambertian emitter it is possible to achieve a smooth beam with a sharp cut-off angle. Reflectors with 10,20,40 and 60 degree beam angles are commonly available. Because of the module’s light emitting area, achieving very narrow beam distributions has an implication on reflector size. Figure 6 shows the relation between the beam angle defined by its Full Width at Half Maximum (FWHM) and the approximate diameter of the reflector for the Xicato module. Efficiency of any reflector is normally associated with size; the larger the reflector the more light can be collected and delivered to the beam. However larger sizes will create problems associated with reflection losses in the coating (the reflection factor of the commonly used aluminium or silver in the visible region is a maximum of 92%, and losses caused by this multiply with each beam reflection).

 Figure 6 Museum Lighting Chart6 resized 600

The relationship between beam angle and reflector diameter for a Xicato Spot module (with a 22mm diameter aperture) 

Until now halogen lamps have been used predominantly in this segment. Xicato’s Artist Series module provides an energy saving, long life alternative with no light quality compromises. 

Figures 7 to 9 show a number of recent museum and gallery installations using Xicato’s Artist Series modules. 

 Figure 7Museum Lighting Chart7 resized 600

The Sunderland Museum and Winter Garden.
Notes:

  • Over 380 “Quartet” Uno track spots and “Quartet” RG recessed gimbal downlights from High Technology Lighting are installed, replacing the previously used AR111 and MR16 halogen.  

 

Figure 8Museum Lighting Chart8 resized 600

Brooker Gallery at the Chicago Field Museum  

Notes:

Here Lighting Services Inc’s LumeLEX™ 2040 luminaires using Xicato’s Artist Series modules are installed. 26 LumeLEX™ luminaires replaced 32 Halogen PAR38 lamps and reduced the wattage from 900W to 400W -a 500W energy savings. In addition, the luminaires were dimmed approximately 40% to achieve the same light levels required for the space by the museum.

 

 Figure 9Museum Lighting Chart9 resized 600

San Francisco MOMA (Museum Of Modern Art).  

Notes:

  • Lighting Services Inc. replaced 25 Halogen PAR38 lamps with 17 LumeLEX™ 2040 luminaires using the 2700K Artist Series module in the The Djerassi Gallery. The energy savings amounted to 61%. 2700K Artist Series modules were used, creating a “human” environment according to their head curator for photography.

 

References

  1. Open letter from Mr Dale Kronkright, Head of Conservation at the Georgia O’Keeffe Museum to the Green Task Force of the American Institute for Conservation of Artistic and Historic Works, 30th March 2010 (http://cool.conservation-us.org/byform/mailing-lists/cdl/2010/0361.html
  2. “Colour Degradation of Textiles with Natural Dyes and of Blue Scale Standards Exposed to White LED Lamps: Evaluation of White LED Lamps for Effectiveness as Museum Lighting” by Mie ISHII et al, J. Light & Vis. Env. Vol 32, No 4, 2008 
  3. CIE: Control of damage to museum objects by optical radiation (CIE 157:2004), CIE, (2004) – from which:

Museum Lighting Chart10 resized 600

* No conservation limit but there may be adaptation, visibility or heat effects if high light levels are used on irresponsive items.

Acknowledgements

To Kevan Shaw of KSLD, Prof. Dr.-Ing. Heinrich Kramer, FPLDA of LICHTDESIGN-Ingenieurges.m.b.H. and Dale Kronkright of The Georgia O'Keeffe Museum and Research Centre for pre-publication reviews of this paper.

Afterword 1

Dale Kronkright, Head of Conservation at The Georgia O'Keeffe Museum and Research Centre

Having reviewed this article and seen Xicato’s Artist Series module I agree that in this instance the problems I highlighted in my letter (reference 1 above) have been well addressed. I would go so far as to say that this remarkable LED module holds a bright beacon of hope for the future of SS lighting. I must however lay down a warning that from my experience it is far from being the norm in the LED lighting field and vigilance in specification is called for to avoid great potential harm to light sensitive materials. Xicato’s Artist Series module does lead the way in our industry and I hope others will follow and museum and gallery lighting can enjoy the energy and maintenance savings of LEDs with no drop in viewing standards or worries about exhibit damage.

Afterword 2

Prof. Dr.-Ing. Heinrich Kramer, FPLDA, LICHTDESIGN-Ingenieurges.m.b.H.

My office having completed over 30 museums in different countries, I am very much convinced by the Xicato Artist Series module. 

Three points on the article:

  1. There is much less belief nowadays in the Kruithof curve. The preferences for the Color Temperature of artificial light are influenced by our experience with daylight and artificial light sources. Thus museum directors all over the world prefer in art galleries with paintings of the old Dutch masters the PAR 38 lamp (Color Temperature of 2500K), because they know these paintings are painted under gas or candle light. So maybe Xicato should also develop a LED with a lower Color Temperature.                                                                              
  2. The deep red parts of the spectrum effect also dark browns (you can see it also in the CRI of the Color sheet R9). Maybe you can add a bit more long wave red. The overall CRI is fantastic, but this is what museum directors require.
  3. There is a trend away from scallops over exposed paintings and towards usage of projectors or wallwashers.

Comments

The information is quite useful and full of innovative ideas. 
I would like to hv some more practical demonstrations 
Posted @ Monday, July 26, 2010 9:31 PM by A K Gupta
This is great info. It is important to hear what conservators are saying. Much available info is, of course, from the Lighting Industry which is glowing (no pun intended)
Posted @ Tuesday, October 26, 2010 8:05 AM by Jane Smith Stewart
Are there any data comparing the use of LED lighting to compact florescent lighting for museum situations?
Posted @ Tuesday, February 15, 2011 1:49 PM by
Congrats on being one of the few to mention the reduction in labor costs from replacing bulbs. I'd always wondered about the color degradation potential on some things. Thanks for uh "shedding some light on it." 
Sorry, bad joke.
Posted @ Tuesday, May 31, 2011 12:36 AM by www.Boat-LED.com
Thank you for explaining The Kruithof curve. Just yesterday I saw dimmable LED device for residential use. Are there any studies as to the denigration of the actual art from the LEDs?
Posted @ Saturday, October 01, 2011 10:50 AM by John
Fabulous study which help me quite a lot at specifying future led fittings. Thanks for sharing it
Posted @ Thursday, October 13, 2011 9:31 PM by Fernando Rojo
Can you please provide links to the data sets for the graphs, or provide graphs that are at a sufficient resolution that they can actually be read? I'm interested in LED's, but from what I can tell, not enough data about CRI is being provided here to make anything other than a persuaded inference? Am I wrong?
Posted @ Friday, March 16, 2012 3:37 PM by david dacaro
Seeking your recommendation on source for your lights and recessed fixture for an estate in Spain...with priceless art and photographs. 
Can you advise where these lights are available in Spain?
Posted @ Wednesday, September 19, 2012 10:48 PM by Lee Benazuly
LED has used & utilize to many different purposes. The major benefit of using LED lights are: Cost effective and efficient. It consumes less energy but it provide a really excellent output. LEDs last long. It can last for 10 years so you won't need to bother bulb changing too often. Although these types of lights is pricey but think of all the savings in the long run.
Posted @ Monday, August 05, 2013 1:11 AM by Amber Smith
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