LED as a light source for sensitive objects

[mike hascall]

Wow. And I thought LED was the future of all lighting. Thanks

[Kurt Christian]

Date: 22 Apr 2010
From: Jim Druzik <jdruzik [at] getty__edu>
Subject: Caution urged when considering LED light sources for
light-sensitive materials

Several points in recent museum lighting posting on solid-state
lighting are inaccurate--the first being that LEDs have CRIs of 60
at best. While there are many sub-par LEDs in the market with poor
color quality, some of the better white, phosphor-based LEDs have
color rendering index (CRI) values over 90 with acceptable
correlated color temperature (CCT). However, recent work by the
National Institute of Science and Technology (NIST) has revealed
flaws in the CRI metric which can result in understated color
rendition for LED sources. For more information on their work,
visit their website:

<URL:http://www.nist.gov/physlab/div844/grp05/vision_color.cfm>

It is essential to recognize that all lighting, regardless of source
type, can cause a sensitive object to deteriorate over time. Fading
is just one color appearance change. Color relationships can be
altered from darkening and shifts in hue. Further, damage can
extend to substrates inducing embrittlement, crosslinking, and loss
of other mechanical properties in paper, textiles, and many
polymeric materials.

Museum lighting research is ongoing to determine the characteristics
of the safest light source for sensitive objects. Unfortunately,
there is only one study (by Ishii, Mie et al., published by the
Illuminating Engineering Institute of Japan in 2008) that has
evaluated LED lighting and its affect on dyed textiles. Apart from
the Ishii study, there is a lack of test data on this issue, and the
use of LED lighting on light-sensitive objects in museums begs for
more research attention.

In addition to fundamental safety concerns, when a new technology is
considered for energy savings and/or maintenance reasons, perceived
brightness and quality must be at least equivalent to that of the
currently used light source. We urge any organization currently
using or interested in using LEDs to do some basic analysis of each
LED product under consideration. In addition to visual evaluation
of an LED product, ask LED manufacturers to provide credible,
standardized IES LM-79 test reports from a qualified testing lab for
every LED product under consideration. These reports should provide
the spectral power distributions (SPDs) of the specific LED product,
along with CCT, light output, power, CRI and luminous intensity
distribution. LM-79 test reports are essential in determining
whether a LED light product has characteristics similar to the lamp
currently in use in your institutions. Qualified test labs can be
found by visiting

<URL:http://www1.eere.energy.gov/buildings/ssl/test_labs.html>

An IES LM-80 test report showing lumen maintenance data for the LEDs
used in the product should also be provided by the manufacturer;
this information, along with an appropriately detailed warranty, can
help ensure maintained output and color over the product's rated
life. More information, including a variety of useful LED fact
sheets, is available on the solid-state lighting website maintained
by the U.S. Department of Energy at

<URL:http://www.ssl.energy.gov>

LED technology is evolving rapidly, and new products are entering
the market every day. Knowing how to choose quality lighting
products takes some effort, and this fundamental knowledge should be
assembled and shared. In the near future, the Research and Technical
Studies group of the American Institute of Conservation will take up
just how they may facilitate and provide such a shared environment.

The Department of Energy supports a program entitled the
Commercially Available LED Product Evaluation and Reporting
(CALiPER) program. This site has a wealth of information on it, not
all of which is equally easy to locate. The following links will
help in finding further information on solid-state lighting (SSL).

CALiPER Program
<URL:http://www1.eere.energy.gov/buildings/ssl/caliper.html>

CALiPER's Searchable Database
<URL:http://www1.eere.energy.gov/buildings/ssl/search.html>

CALiPER Benchmark Reports:
<URL:http://www1.eere.energy.gov/buildings/ssl/benchmark.html>

In particular:

The most recent Round 9 Caliper report (long term
testing/Reliability)
<URL:http://apps1.eere.energy.gov/
buildings/publications/pdfs/
ssl/caliper_round-9_summary.pdf>

Color Rendering Index and LEDs
<URL:http://www1.eere.energy.gov/buildings/ssl/cri_leds.html>

Color Quality of White LEDs
<URL:http://www1.eere.energy.gov/
buildings/ssl/color_quality.html>

LED Lifetimes:

<URL:http://www1.eere.energy.gov/buildings/ssl/lifetime.html>

<URL:http://apps1.eere.energy.gov/
buildings/publications/pdfs/ssl/lifetime_white_leds.pdf>

LED Luminaire Reliability
<URL:http://apps1.eere.energy.gov/
buildings/publications/pdfs/
ssl/Luminaire_Reliability.pdf>

Understanding Photometric Reports for SSL Products
<URL:http://apps1.eere.energy.gov/
buildings/publications/pdfs/ssl/
understanding_photometric_reports.pdf>

Energy Star Criteria for SSL
<URL:http://www.energystar.gov/
ia/partners/product_specs/program_reqs/SSL_prog_req_V1.1.pdf>

DOE GATEWAY Demonstration Reports
<URL:http://www1.eere.energy.gov/
buildings/ssl/gatewaydemos_results.html>

Next Generation Luminaires--Design competition winners
<URL:http://www.ngldc.org/09/winners.stm>



**** Moderator's comments: The above URLs have been wrapped for
email. There should be no newlines.

Jim Druzik
Senior Scientist
The Getty Conservation Institute

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