This article originally appeared in the May/June 2012 issue of Museum magazine.
Tungsten illumination—familiarly known as the traditional light bulb with a glowing tungsten filament— dominated indoor lighting during the early 20th century. Fluorescent tubes and tungsten halogen lighting followed later. More recently, a greater concern for the environment, demand for energy efficiency and the rising cost of electricity have been slowly changing the market with the introduction of compact fluorescent bulbs (CFLs), small high intensity discharge lamps (HIDs) and fi nally white light-emitting diodes (LEDs). With a broad range of unique designs, LEDs can look like almost any light source they replace. LEDs take a leading role as museums decide or are compelled by legislation or national policy to make this change to convert to more efficient light sources. All museums struggle to balance their needs for cost-efficient operation, high aesthetic values and preservation. White LEDs meet the highest standards of aesthetics and preservation while also offering outstanding operating advantages at a reasonable payback.
How do LEDs promote sustainable goals in museums?
Although not perfect, LEDs are efficient in converting electrical energy into light. It’s not unusual for LED use to save 85 percent in electricity consumption as compared to other illumination. They can also potentially last for decades before needing replacement and often come with a limited warranty against failure. Few traditional light bulbs have that option. Long life reduces the labor cost of replacing burned-out lamps, especially in very high places requiring scaffolding. Finally, they don’t contain heavy metals in any significant quantity, and their lower power use even results in fewer mercury emissions created by power plants. For institutions in temperate climates, for every three watts of electricity saved in lighting, the lower heat load saves one air conditioning watt. The sustainability benefits are mounting.
Is the color quality of LEDs as good as incandescent lamps?
Probably. Manufacturers use two metrics called Correlated Color Temperature (CCT) and Color Rendering Index (CRI) that help answer this question. If we heat a non-reflective material until it glows, we can define the color of that light by the temperature that caused it. Traditional tungsten light bulb filaments can endure high temperatures, so their color temperature is approximately 2800K. If you want a light source to match the tungsten glow you’re accustomed to, you attempt to approximate that color temperature. CRI measures how well a light source matches an incandescent one at the same color temperature, using a standard set of color swatches. Even an art museum can use light sources with CRIs above 80. Color quality is frequently more a matter of individual human preference than lamp choice. Fortunately, LEDs exist in a range of nuanced “whiteness” to satisfy anyone.
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Unlike most other light sources used for exhibition or display, white LEDs emit no ultraviolet or infrared radiation. Ultraviolet radiation is of higher energy than visible light, so it is capable of inducing light damage at a greater rate. On the other end of the visible spectrum, LEDs radiate no infrared that can cause excessive heating and drying—a significant issue with furniture and composite structures like polychrome sculpture. Not all LED lamps are recommended for museum use, but of those that are, the LED lamp’s spectrum tends to match incandescent varieties so closely they render colors nearly identically to incandescent lamps. Thus an LED with the same color temperature as a traditional incandescent display lamp is usually a good match in color, a better choice for preservation over the long term and highly efficient.
Do LEDs produce more glare than standard track lighting?
Glare is a reality with any light source, but good lighting design and fixtures prevent it. Direct glare is caused by high contrast between the source and the background. When the lighting source is small like an LED, the glare potential is increased. Scott Rosenfeld, lighting designer at the Smithsonian American Art Museum and the Renwick Gallery, recommends using fixtures with lamps recessed several inches inside the opening, or installing a “cutoff” louver that blocks a visitor’s direct view of the bright light source. A 45-degree cutoff is ideal, and any louvers should be painted matte black. He also suggests lamps that produce narrow beams and which are spaced closely along the track. Not all LEDs are made the same way. For example, the Cree LRP38 lamp shields the intense light-emitting surface away from direct view, bouncing the light against a reflector before it is emitted from the face of the lamp. This provides very precise beam control as well as glare control. Other manufacturers provide clip-on reflectors or plastic lenses that increase the surface area of the lamp.
James Druzik is senior scientist, Getty Conservation Institute, Los Angeles, and has run a museum lighting research group for the last 10 years. He can be reached at firstname.lastname@example.org.