PDA

View Full Version : More on LED from the listserve



T. Ashley McGrew
12-04-2010, 06:44 PM
Tue, November 30, 2010 2:41:45 PM
Led lamps

From:Jim Whiteaker

Hi all

I recently read about several major museums switching to the new LED lamps and was wondering if anyone has had experience with them and where I could get information? We may be expanding and are considering the new lamps. Any help would be greatly appreciated.

Jim
__________________________________________________ __________

Jim Whiteaker Exhibition Manager Hearst Art Gallery St. Mary's College of California
P.O. box 5110
Moraga, CA 94575-5110

Tue, November 30, 2010 3:36:51 PM
LED lamps



From:Dale Kronkright conservator@okeeffemuseum.org

I was one who voiced concern over the early adoption of LED illumination sources on light sensitive materials. I have read Steve Weintraub’s post, published on the AIC’s web site by the AIC AIC's Committee on Sustainable Conservation Practice ( http://www.conservation-us.org/_data/n_0001/resources/live/Response%20from%20Steve%20Weintraub.pdf ) and have spoken to Steve personally, many times. I think that it is fair to say that, at this juncture, we disagree about the inherent safety of multi-phosphor, white LED’s. All of Steve’s data regarding the spectral output and relative energies of the output spectral emission peaks is rock solid. But my own fading tests suggest that all is not as it seems. I have not countered posted my arguments, previously because James Druzik and the Getty Conservation Institute have a rather intensive experimental protocol in the works ( see “Component six: http://www.getty.edu/conservation/science/lighting/lighting_components.html ) that may, excuse the pun, shed additional light on this argument! Plus, we just disagree and there’s little use in us pitching our arguments back over and over, ad nausea.

My fear is that “relative damage potential” turns out to have little to do with the discoloration of light sensitive materials. In the museum world, “light sensitive materials” are defined as those materials that undergo color changes – fading, yellowing, darkening or color-shifts – when exposed to the human visual light spectrum, with all UV and IR removed; in essence, exhibition light. More light-stable materials undergo changes that more strictly follow the “damage potential” of a spectral distribution curve. But light-sensitive materials undergo damage as a result of their absorbed wavelengths. Although the reaction chemistry is complex, damage is initiated by a narrow range of colors that are absorbed by the coloring molecules. So for these materials, blue light does not necessarily do more damage than green, green more than yellow, yellow more than red, etc. Vermillion seems to undergo darkening when exposed to normal museum exhibition light and cool white light does the damage no faster than warm-white light. It seems that it is light in the green wavelengths that may be initiating the damage. So any light source - LED, fluorescent, HID-metal halide, filtered incandescent- that emitted more light within the green wavelengths than an normal incandescent source might do damage to vermillion at rates much faster than predicted by all museum data.

So what to do? These days we test light sensitive materials using the Micro-Fade tester and we calibrate the rate of damage using ISO British blue wool standards because we all have understood the behavior of the now 30-year-old BBW cards in museum lighting conditions (up to now, incandescent-halogen sources) rather well. The spectral distribution curves of LED sources are notably varied from manufacturer to manufacturer and considerably different than that of incandescent sources, with the sole exception (in my testing) of the Xicato Artist Series dual phosphor dome light source ( http://www.xicato.com/downloads/Museums,%20PLD%20Magazine,%20July%202010.pdf ). That means that we have no idea how a tested light sensitive material will really behave under LED’s, fluorescent lamps, HID-metal halides or any other light source other than the standard incandescent, with the reasonable exception of the Xicato LED source. So right now, I do not believe, as Steve Weintraub does that “based on current knowledge, both low to intermediate color temperature white phosphor-based LEDs (2700K-4000K) and tungsten halogen lamps are safe if used at an appropriate light level for museum applications.” We may find that for the large majority of light-sensitive museum materials, all the white phosphor LED’s on the market are safe facsimiles to incandescent sources. But right now, I remain very skeptical of the inherent safety of all but a very small sample of tested white LED sources.

Dale Kronkright
Head of Conservation

GeorgiaO'Keeffe Museum

dkronkright@okeeffemuseum.org (dkronkright@okeeffemuseum.org)
217 Johnson Street Santa Fe, New Mexico 87501
USA

++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++
Dale,

Thanks for your response to this ongoing enquiry. The specifics you provide here are greatly appreciated.
I have been attempting to keep up on this topic and have been in communication with a number of good folks along the way.
So far though, what I find to be strikingly absent are specifics. The kind of specifics required to do our job(s).

I do understand that there are a number of fairly complex variables to consider.
With all of the advocates of LEDs, whether based on a "green" perspective or whatever, what I have not been able to establish are exactly what products are being used, by what institutions, and what testing has been done on them.
Screening new materials and technologies is a constant aspect of our profession.
One thing that we all know is that historically, for every advancement there are an equal number of horror stories where people ill-advisedly jumped on a bandwagon headed straight into a ditch and the objects were the casualties.
Folks like us are charged with actually delivering on all of this stuff, and along with that fact comes ultimate responsibility for any damage that may result by mindlessly following the latest fad.

Simply put we just need to know what is safe to use - really - based on.....something!!


To reiterate we need to know ....
1) What products (especially valuable if they compatable with existing fixtures) are being used?
2) What reputable institutions have adopted their use?
3) What testing has been performed on these products and by who?

In my view, these are fairly minimal requests that really need to be addressed before the use of these products can be considered in any responsible institution.
So far I have pretty much been drawing drawing a blank on most of this. Lots of theory and almost no specifics
Anyone out there who can deliver the goods on this one please pitch in.
A bunch of us are eager to make progress with using this very promising technology, but this only true if it is indeed real progress and only if it is responsible in terms of simple sound stewardship.


Of course as well, as an "Information Network" PACIN is only too happy to distribute this kind of information - widely.
Lacking the three steps mentioned above though ..... not so much.
Regards,

Ashley