The easiest way to understand light damage is to understand that
basically that all light will damage light sensitive media. That
damage is cumulative and irreversible and it is the light energy
(intensity) and duration of exposure (time) that lead to smaller or
greater light damage effects on collections.
Many people make the mistake of thinking that by eliminating the UV
component of light that you eliminate the damge. You do not. You
simply are removing or blocking the most damaging part of light, and
thus are slowing the speed at which the irreversible damage will take
place.
There are so many sensibile strategies in regards to this - from the
frequent rotation of light sensitive colllections on display, to lower
light levels, blocking or eliminating UV light, to using push buttons,
timers, or sensors to turn on and off lights only when the exhibits
are being viewed, and yes using the best light systems and sources. In
historic houses you can turn down the blinds and draw the cutains
during the high exposure times of the day, you can also make sure that
sensitive media isn't in front of a window getting blasted every day.
As Marc Williams can well attest, it isn't just silks and paintings
that get damaged, there are so many examples of historic furniture
that suffers incredible damage from light as well. (conservators are
funny about this, we love to show photos of these kind of collections
horrors!)
As a conservator I can't tell you just how common it is for us to turn
over an object, see it's reverse side, and discover the vibrant
colors and finishes that were protected from the sun and light.
Cheers!
Dave
David Harvey
Conservator
Los Angeles, California
On 6/1/07, Marc A Williams <[log in to unmask]> wrote:
>
>
>
>
> Résumé / AbstractCurrently, 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
>
> *Collections Preservation Consultation
> *Conservation Assessments & Surveys
> *Low-Tech Environmental Control
> *Moisture Management Solutions
> *Collections in Historic Structures
> *Conservation Treatment of:
> Furniture
> Painted Wood
> Horse-Drawn Vehicles
> Architectural Interiors
>
> 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: Paul Fritz
> To: [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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