Demonstration of LED Retrofit Lamps at the Smithsonian American Art Museum, Washington, DC Page: 38 of 54
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An electronic-transformer track luminaire is used for display lighting, equipped with a GE "Constant
Color" 50W MR16 400 FL halogen lamp. The lighting system in the Luce Center Gallery is controlled by
a Lutron dimming system, with a reverse phase ("ELV" or "trailing edge") dimmer for this type of load.
Knowing that electronic transformers and dimmers can introduce incompatibilities into the lighting
system, the lighting designer was willing to reprogram the dimming system so that it delivered "full
output" or was "off," but was never a significant phase-cut waveform to the replacement lamps.
However, little could be done about the electronic transformer, since magnetic transformers are usually
larger than the housings designed for electronic transformers. (Size was critical because the existing
MR16 fixtures, seen in Figure 20, were specially built to allow the glass case doors to open without
hitting the lighting fixtures.) The lighting designer was determined to find 12V LED replacement lamps
compatible with electronic transformers.
Figure 20. MR16 track heads with electronic transformers used in Luce Center. Photo by Scott
Rosenfeld.
According to the manufacturer, the 50W MR16 halogen lamp delivers about 750 lumens, with CBCP
of 1700 cd. In 2011, there were no true 50W-equivalent MR16 LED replacement lamps that also offered
3000K color and the needed color spectrum. At best, some came close to a 35W equivalent. However,
the lighting designer was also willing to increase the number of track heads to compensate for the reduced
light output per LED lamp as long as a beam angle of 400 or more could be obtained. Over the course of
the year, the lighting designer tested products from 10 manufacturers or more. While every product
showed differences, the following list of unsatisfactory characteristics ultimately prevented LED MR16
lamps from being used:
" Beam distribution: Only one manufacturer offered an MR-16 with a wide angle 520 beam angle. A
beam angle of 400 or greater was necessary to provide an adequate wallwash without additional
lensing that would reduce illuminance and efficacy, or block air flow in the luminaire. Unfortunately,
the next widest available beam angle was only 360.
" Color appearance: The color appearance of some LEDs did not match that of the halogen lighting in
adjacent cases. Some LED MR16 products had a yellowish, bluish, or pinkish cast, compared to the
incumbent halogen. (In fact, the halogen lamps tended to appear slightly green compared to the LED
lamps, but the museum staff was trying to maintain the appearance of the halogen lamps.)24
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Miller, Naomi J. & Rosenfeld, Scott M. Demonstration of LED Retrofit Lamps at the Smithsonian American Art Museum, Washington, DC, report, June 22, 2012; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc828649/m1/38/?rotate=270: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.