Review of the webinar Introduction to LED Lighting

__NOTOC__
Back to 4.6 Lighting
Heritage Preservation: Connecting to Collections
Introduction to LED Lighting
Richard Kerschner, Director of Preservation and Conservation and Nancie Ravenel, Objects Conservator, both of Shelburne Museum in Shelburne, VT gave a presentation on LED lighting that helped bring some updates in the field to the forefront. It was noted that while 83% of those surveyed are not currently using LEDs, most have expressed an interest in using them. It has only been since about 2010 that LED retrofit lights have improved to the point of being bright enough and maintaining pleasing and consistent color temperature to replace the commonly used MR 16 Tungsten-Halogens. The technology continues to rapidly evolve and while there are many acceptable LED lighting systems available, there is a desire for more information on LED retrofits for existing tungsten-halogen track fixtures.
Kerschner provided information on how to select LEDs (for retrofits) and how to interpret the information found on the labels of available products. “Life” refers to the amount of hours before the light diminishes to 70% of the original output. Center Beam Candle Power (CBCP) denotes the brighter center of the light – noting that the higher the number the more the light acts as a spot versus a floodlight. Diffusers and spread lenses can be used to achieve more of a flood appearance. Kerschner also suggested that we in the field be aware that light output for LEDs is measured in Lumens (as opposed to foot-candles or lux). Although “payback” time for LEDs is often cited for comparison to incandescent bulbs, this can vary greatly depending on the specific bulb, the condition, and any rebates or similar incentives available to bring down costs.
It was suggested that, for retrofits, it may be best to stick with well-known manufacturers such as Phillips, Sylvania, or GE. Even going with well-known manufacturers though Kerschner advises buying several types and doing mock-ups to test what works best in your situation. Some LEDs are dimmable (more are becoming available) but may not work on all dimmers for track lighting – the LED needs to be matched to the dimmer. One also needs to be aware that some MR16 transformers are not able to handle to low wattage of LEDs. This may cause LED retrofit bulbs to flicker or to not light at all until a minimum load is attained, i.e., several heads containing low wattage LEDs are attached to the track. 
Kerschner and Ravenel also noted the work done by Joe Padfield, at the National Gallery, London, who has published an excellent resource for comparing various light source spectral distribution curves . As Jim Druzik of the Getty has noted concerns over “hole-burning” were based on studies of narrow-band LEDs that have been mostly replaced by white LEDs. Improvements in the Color Rendering Index (CRI), coupled with neglible UV and IR levels, have started to meet the demands of the museum field but there is still a concern over the ability of the lamp to maintain intensity and the same color over its lifetime.
From their tests at Shelburne, Kerschner said after staff evaluation of several lighting mock-ups, the Sylvania ULTRLED Par 20 and 30 and the Phillips EnduraLED MR16 were chosen as the best LED retrofit lights for viewing artifacts Shelburne’s galleries and historic structures. The best results were attained with 3000K to 2700K LEDs. The 3000K, having a slightly bluer cast, illuminated paintings and colorful decorative artifacts nicely. The 2700K LEDs generate a warmer yellow light that better illuminates unpainted wood walls and ceilings and large dark artifacts such as horsedrawn vehicles. Ravenel noted that the color temperature of LEDs could influence choices made in wall-color, and of particular note for conservators, loss compensation. She said walls and cases painted a lavender color looked different under the LED lighting and that a fabric insert that matched well under the conservation studio light, was more noticeable when viewed under LED gallery lighting. Ravenel recommends that conservators note what light will be used to illuminate the artifact and have that light available for inpainting or color-matching in the conservation lab.
Kerschner also discussed LEDs in case lighting, showing examples from Shelburne.
Working with the manufacturer Prolume, Inc. Shelburne developed a system for their cases that was revised and improved as LEDs improved over a three-year period. He noted LEDs were a far better choice for their institution than fiber optics which would have emitted an excessive amount of heat from the light sources and would have cost in excess of $130,000 to light their doll cases. Working with the Prolume and with support from the energy saving public utility they were able to use LEDs for the cases for a cost of about $30,000. 
Finally, in response to a question, Kerschner mentioned that currently manufacturers are making LED lights in candelabra styles for historic light fixtures. Some of these lights could even flicker to imitate candles and be used in chandeliers. He noted that LED picture lights are also available. More information on LED lighting at Shelburne Museum can be found on their blog. 
Credits: This information was presented on a webinar on the Connecting to Collections Online Community , which is moderated by Heritage Preservation in cooperation with the American Association for State and Local History and with funding from the Institute of Museum and Library Services. The site is designed and produced by LearningTimes.
 
Here’s a link to the recording of the webinar, and resources.