Résumé / Abstract

Currently, the highest color rendering index (CRI) value obtained in commercially available LED devices is around 90. This falls short of the CRI values typical for incandescent lamps (defined at 100). Similarly, the commercially available LEDs for higher color temperature have CRI values of 65-85, well below the theoretical maximum of 100. New phosphor blends are proposed for use with LED chips emitting in the 350-450 nm range. The application of such blends can afford CRI values greater than 95, over the entire range of color temperatures of interest for general illumination (2500K -8000K). In some cases, the CRI values approach the theoretical maximum of 100. LED based lamps with a steady state performance of 23 LPW and 25 lumens per chip at 3000K, with a general CRI (Ra) of 97 and a mean CRI (R1-R14) of 96 are demonstrated.

Pulled from a quick Google search. Current CRIs for LEDs are lower than other options in the daylight (5000-6500K) range. Thus, they are probably not ideal for museum lighting. Note from above that new phosphors are proposed in the 350-450 nm range, that will bring CRI up into the 90s, or equivalent with other sources. HOWEVER, 350-400 nm is in the UV range, so these new light sources will probably emit UV light!! Stay tuned....

Marc

American Conservation Consortium, Ltd.
     4 Rockville Road
     Broad Brook, CT 06016
     www.conservator.com
     860-386-6058

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Marc A. Williams, President
     MS in Art Conservation, Winterthur Museum Program
     Former Chief Wooden Object Conservator, Smithsonian Institution
     Fellow, American Institute for Conservation (AIC)

----- Original Message -----

From: [log in to unmask] href="mailto:[log in to unmask]">Paul Fritz

To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]

Sent: Friday, June 01, 2007 11:18 AM

Subject: Re: [MUSEUM-L] Museum lighting

Another aspect to remember.

I can't remember off-hand who I had a good email conversation with regarding LEDs, but he mentioned to me that the CRI was an important aspect worth considering. This is the measurement of how light renders the color of objects. The wrong color light will make objects look weird (think of a blue light on a white surface will make the white surface blue).

There are a few LED manufacturers (Luxeon) that make LEDs with a warmer color temp, but I really don't know what the CRI for them is. I have used the bright white Luxeons (not the warmer color) in an exhibit with great success, but I was illuminating a sky, so the trace blueness of the light made it look good.

I'd recommend trying an example of several lamps to find the one that would best approximate what you are looking for.

Oh, and to echo Marc, from my understanding, light damage is cumulative. Any time an object is exposed, it adds to the damage, so these lamps really only delay the damage by removing unnecessary UV. The best thing to do is limit the overall illumination to the lowest level possible.

Paul Fritz

--
Paul C. Fritz
Pamplin Historical Park & the National Museum of the Civil War Soldier
6125 Boydton Plank Road
Petersburg, VA 23803
(804) 861-2408 -- Tel
(804) 861-2820 -- fax
Visit us at
www.PamplinPark.org
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