LED as a light source for sensitive objects
Here is a recent post sent out on the Registrars Committee listserve as a result of strong interest in discussions on the PACIN listserv on this very current topic (this is one of two parts) :
Hello Museum folk,
With the strong emphasis on "green" technology these days there has been a movement towards the use of LED lighting in cases and galleries.
As part of a recent discussion on this topic on the PACIN listserv a post by Dale Kronkright - head of conservation for the O'Keefe Museum and including a quote from Jim Druzik of the Getty Conservation Institute struck an alarming cord. With both individuals permission I would like to pass that post on to Museum-L folks.
Those of you who are also on the RCAAM listserv may have seen it - if so my apologies for the repetition.
Obviously there are previous posts about poor CRI ratings typical of LED and the important distinction between Color Temperature and Color Rendering (in the form of a light sources CRI - Color Rendering Index) that are not included here.
For people whose jobs include the responsibility for making informed decisions concerning the safe handling, packing, crating, installation, and storage of cultural materials I would recommend taking advantage of the PACIN (Packing, Art handling, and Crating Information Network) website and listserv as a resource.
Anyone interested can either join the listserv themselves or simply request that those individuals who are the hands-on preventive conservation practitioners within their institutions do so.
Here is the post and some additional comments provided by Dale Kronkright:
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From: Dale Kronkright <conservator@okeeffemuseum.org> [Add to Address Book]
To: pacinlist@pacin.org
Subject: Extreme caution urged when considering LED's for illumination of light-sensitive materials
Date: Mar 24, 2010 8:46 AM
Attachments: Hole burning potential of LEDs.pdf unknown-135 B
Below is a letter sent to the Green Task Force of the American Institute for Conservation of Artistic and Historic Works, at their request, clarifying the potential problems of using LED’s to illuminate art cultural heritage materials. Members of the task force suggested we also post this email to the PACIN list serve. First let me say that LED’s present a low-energy-of-operation alternative for the illumination of non-light-sensitive museum materials where the color discrimination of the object is not critical to its appreciation or understanding and in offices and non-collection areas.
I believe the existing reported data demonstrates that LEDs are a potentially damaging light source for light-sensitive museum materials and are deficient where accurate color discrimination within the human visible spectrum is required. The deficiencies of LED light sources, both for color rendering and for their narrow emission spectra, is not new information. The CIE data first explaining these deficiencies in detail was published in 2004. I believe the manufacturers are acutely aware of these deficiencies. Jim Druzik of the Getty Conservation Institute has just returned from an NIST meeting where the efforts of the manufacturers to overcome them was frequently discussed. Unless conservators ask very pointed and direct questions, my sense is that manufacturers have not initiated discussions that reveal the risks of LED light sources to light sensitive materials.
The color rendering indexes of these light sources, when tested in independent studies, has been near 60% at best across the entire human visible spectrum. Experimenters have documented considerable human impairment with color discrimination with materials viewed under both 2-phosphor white LEDs and RGBA and RGB 4- and 3- source “white” LED sources. If exposing light-sensitive materials to damage within exhibitions is to severely limited, then certainly the few times they are exhibited ought to be done so that people can accurately discriminate between the colors we are so carefully trying to preserve. To expose them to damage AND prevent an accurate sense of their visual characteristics seems to be the biggest crime of all.
I will attach copies of 2006 un-filtered MR-16 halogen incandescent lamp, a 2-phosphor white LED, a red, green, blue, amber white appearing LED and a red, green, blue “white” appearing LED, each taken off a standard spectralon tile at 660 lux. Each of the SPD’s has a heavy horizontal line at 0.01W·m−2·nm−1 , the highest power output of a broad, continuous incandescent lamp. Please note that the power of the narrow wave peaks produced by the LED’s is 20% to 400% higher than the halogen MR-16 at the same light level.
