Bringing Brilliance. to Light. A Modular Approach to Lighting Enabled by 3M Light Tubes

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1 A Modular Approach to Lighting Enabled by 3M Light Tubes 3M Optical Systems Division 3M Electronics and Energy Laboratory John Wheatley, David Britz, Michael Meis, Vadim Savvateev, Will Edmonds, Gilles Benoit, Ken Epstein, D. Scott Thompson Bringing Brilliance to Light

2 Contents Executive summary...1 A New Design for LED Lighting...2 Demonstration: The 3M Light Tube...3 Singular Advantages...4 Quantum Dots: A Primer...5 Learn More...5 3M s model light design demonstrates how modular components can provide precise light placement, improve thermal management and achieve significant reductions in energy consumption. 3M is also demonstrating a new way to enhance color.

3 Executive summary The technical and economic barriers to wide-spread LED adoption continue to drop. Bright, durable, low-cost LEDs are widely available, and are forecasted to become even brighter, more durable and less expensive in the next few years. (The U.S. Department of Energy estimated that the cost of warm-white LED packages fell from $36 to $18 per thousand lumens from 2009 to 2010 and will drop to approximately $2 per thousand lumens by ) As a result, LEDs are expanding beyond high-value consumer electronic devices (such as televisions, mobile phones and computer displays) into ubiquitous applications, from industrial and commercial lighting to outdoor illumination. Several technical barriers remain, however. These include: Thermal management: LEDs emit about two-thirds the heat of comparable compact fluorescent bulbs and often less than a quarter of the heat of incandescent bulbs. Despite that extraordinary advantage relative to other technologies, heat emission remains a concern because the heat is concentrated in the LED footprint. In some applications, the LED is located in an area where heat can negatively impact the system, for example in food and refrigerated display cases. This heat can increase system costs because of damage to illuminated products or additional power required to remove the heat. Light transport and delivery: As LEDs have improved in output, efficiency, and cost, their advantages and use relative to competing sources (fluorescent and incandescent) have increased as well. Initial applications of LEDs in distributed area lighting use arrays of large numbers (hundreds) of LEDs. The heat is distributed with the source, and achieving directional control and light quality can be also challenging. Importantly, the improvements in LED output, efficiency, and cost now enable pairing with new light distribution technologies that enable remote sources, enabling systems with key advantages over arrays. 2 Color: LEDs without phosphors generally emit blue light. Phosphors in the LED package are generally used to provide a more balanced color spectrum, but can have angle-dependent color and generally do not provide good rendering of longer wavelengths. Color variations among LEDs can also be significant; this creates added costs for selecting LEDs from specific bins or bin ranges. 3M is demonstrating a modular light design that addresses the first two technical barriers (thermal management and light transport), and improves key aspects of the third (color uniformity). By addressing these limitations in current LED systems, the model design allows for increased efficiency and the potential for significant reductions in energy use in important applications. This modular light design achieves these results by efficiently transporting light, separating LED illumination from LED heat, and thereby enabling higher system efficiencies. The design employs 3M s light management materials, which efficiently guide, mix, and shape light to deliver the required output while minimizing optical losses. It also provides an opportunity for a highly efficient solution for improving color uniformity (reducing or eliminating LED color variation effects and angle-dependent color). 3M is making this model design available to the lighting industry to enable progressive end users to advance and differentiate their lighting solutions while simplifying their supply chain. 1 U.S. Department of Energy, LED Frequently Asked Questions, May 2011, 2 J. Wheatley, et al. Efficient LED light distribution cavities using low loss, angle-selective interference Transflectors, Optics Express, Vol. 17, Iss. 13, pp (Jun. 22, 2009). 1

4 A New Design for LED Lighting 3M is among the world s leading authorities in managing light. The company s multilayer, nonmetallic mirror films, light-directing optical films and reflective polarizers made the first LCD TVs, laptop computers, and mobile phones a practical reality. 3M has now adapted several of these technologies for use in LED lighting. Its model light design consists of an LED light engine and a polycarbonate tube that has been partially lined with highly reflective (> 98 percent) 3M Enhanced Specular Reflector (3M ESR) mirror film. A section of the tube s length is not lined with ESR; this creates an aperture that runs the length of the tube. The aperture is covered with a strip of microstructured, lightdirecting film (Fig. 1). LED Polycarbonate Tube 3M ESR Aperture with light directing optics LED Figure 1: 3M LED lighting model architecture, side and end view. Light from one or two LEDs is injected into a polycarbonate tube that has been partially lined with 3M ESR mirror film; the light escapes through an aperture that runs the length of the tube. As light escapes the tube, it is concentrated and directed by a microstructured film. Light is injected at one or both ends of the tube. The 3M ESR reflects the light multiple times, transporting it down the tube and mixing it to produce a uniform color and distribution. As the light propagates down the tube, a portion exits through the aperture with each bounce. As it exits the tube, the light is concentrated and directed by the microstructured film, resulting in an engineered light distribution pattern light where you want it. LED 3M ESR Aperture with light directing optics LED Light Directing Optics Figure 2. The illumination pattern can be changed by changing the microstructured film. This model can be adapted to achieve various configurations of brightness, illumination area, and distribution. Changing just one component allows for a wide range of potential products. It also provides an elegantly simple architecture where different light output distributions can be achieved by using different replicated structures for the aperture. Figure 3. Examples of types of illumination patterns that can be created by altering the microstructured film. 2

5 Intensity Cross Section Intensity Polar Angle (degrees) Figure 4. Angular output of the 3M Light Tube: Angular distribution for lengthwise (0 ) and orthogonal (90 ) axes. By changing the configuration of components, 3M s modular design allows for precise directional control of LED light. The output distribution for one configuration model is depicted in Figure 4; in this example, the distribution is very narrow along one axis and broad along the other. By altering the components particularly the light-directing microstructured film covering the aperture other output distributions can be achieved. Demonstration: The 3M Light Tube The 3M Light Tube is a demonstration of the model design enabled by 3M s component approach to lighting. One application of the 3M Light Tube is in refrigeration display case lighting, where its design provides excellent illumination along with a very significant reduction in energy consumption. This application is timely given new energy efficiency standards proposed for commercial and walk-in refrigerators. To demonstrate this application, an 18 ft 3 (510 L) commercial vertical refrigeration display case was retrofitted with a 3M Light Tube system. The system incorporated two 56-inch long, 1-inch diameter 3M Light Tubes, each with a light output of 550 lm and an efficacy of 80 lm/w. Overall efficiency (3M Light Tube output/light engine output) is 88 percent. Figure 5. The 3M Light Tube demonstrates the model design enabled by 3M s component approach to lighting. Power Input for Light Source Compressor Power for Cooling Light Source Total System Power Number of LEDs Fluorescent (65W) 65 W 20 W 85 W LED Strip 35 W 27 W 62 W 288 3M Light Tube 14 W 10 W 24 W 4 Table 1 compares the heat and total system power use for this cooler using three lighting systems: 65-watt fluorescent bulb, strips of discrete LEDs (288 in total), and an LED system using two 3M Light Tubes. Each 3M Light Tube was illuminated with two LEDs (one at each end) for a total of four LEDs. Table 1. Comparison of three lighting systems for a refrigeration display case. 3 See: Juliet Eilperin, Obama Administration Proposes New Energy Efficiency Rules, Washington Post, 29 Aug

6 Optical measurements were made on the brightness and uniformity at a representative target plane in the cooler. The 3M Light Tube system produced comparable brightness and improved uniformity compared to the LED strips. The differences in energy consumption were notable. The 3M Light Tube system requires just 24 watts (for lighting and cooling) 72 percent less than the power needed for a comparable fluorescent lighting system and 61 percent less than the power required by an LED array lighting system with comparable illumination. The 3M Light Tube system enables this large energy reduction because it requires less energy for light generation and less energy for refrigeration (since it introduces much less heat into the cooler). The LED engines of the 3M Light Tubes are capable of being placed outside the thermal envelope of the refrigerator and are thermally coupled to the refrigerator door s metal frame, using the structural members as heat sinks. For this example 10W of heat was generated, and improvements toward zero watts are possible. These results are notable in their own right, and serve as an indicator of the potential inherent in this modular approach to lighting design. By changing components particularly the microstructure on the light-directing optical film that covers the aperture the distribution of light can be tailored to achieve the optimum efficiency, thereby reducing power requirements. Additionally the remote source enables innovative approaches to thermal management. Singular Advantages As noted earlier, the 3M Light Tube is designed to provide bright, uniform, highly efficient illumination. The model light design s efficiency and scalability make it suitable for illuminating a variety of spaces, from small coolers to large rooms. Other advantages include: Modularity: each of the key components can be modified individually to best suit the specific lighting requirements of the application. Lighting designers also have the option to purchase either individual films or assembled lighting units from 3M. Design freedom: unique lighting effects and form factors can be achieved by altering any of the model light design components. From a luminaire standpoint, these directional control lamps change the traditional paradigm in which the light source emitted light and the luminaire provided the directional control. With the lamp providing directional control, new design freedom exists for luminaire innovation in cost, performance, and style. With the lamp providing directional control, new design freedom exists for luminaire innovation in cost, performance, and style. SKU reduction: the model light design s flexibility allows simple changes in configurations to achieve different distributions. This, in turn, allows one base fixture design to provide a variety of outputs by changing only one component. Quantum Dots: A Primer 4

7 Quantum Dots: A Primer The model light design also provides a unique opportunity to change the spectral distribution of LED light and hence color quality by incorporating remote phosphor or quantum dots into the lighting system. Quantum dots are nanoscale spheres of semiconductor materials. A quantum dot will absorb relatively short wavelengths of light and emit a narrow spectrum of light at longer wavelengths. Smaller dots produce shorter wavelengths; larger dots produce longer wavelengths. By adjusting the quantum dot coating formulation, one can produce a wide range of emission spectra with engineered shapes, peaks, and designed color attributes. Because the wavelength of the emitted light is determined by the size of the dot, the emission is predictable and tunable. When the light from a blue LED strikes a 3-nanometer quantum dot, it emits narrow wavelength green light. When the blue light strikes a 7-nanometer dot, it emits a narrow wavelength red light. By controlling the size of the dots, the spectral output of the lighting unit can be tuned precisely. Alternative methods for changing the color of LEDs such as phosphor coatings or the supplementing of conventional blue LEDs with red and green LEDs are effective but have well known disadvantages. Quantum dots have been considered a promising option for some time, and recently with the help of 3M optical design and film manufacturing capability have been introduced to the consumer electronics display market. 3M Quantum Dot Enhancement Film (3M QDEF) is an already commercialized method for deploying quantum dots in remote light conversion architectures in liquid crystal displays. Currently, the film (composed of red- and green-producing dots in a matrix material) is being combined with blue LEDs to generate a white light with spectral peaks in the red-green-blue primaries. This output configuration allows LCDs to produce saturated primaries and, in turn, a larger color gamut. When a lighting application calls for a warm, flattering light, the model 3M Light Tube design could allow for a 3M QDEF film to be inserted across the aperture. Photons escaping the tube would pass through the aperture to the 3M QDEF and be converted to longer wavelengths. The spectral output could be precisely tailored to match the designer s specifications for color temperature and CRI. (3M QDEF also has light-diffusing qualities that can soften the light output angular distribution.) Because the aperture in the 3M design is remote from the LED, lifetime of quantum dots would be increased due to the lower incident light flux and operating temperature. Learn More 3M Optical Systems Division continues to refine its model architecture and its first demonstration of that architecture, the 3M Light Tube. The company is eager to share its latest advances and apply its technologies to the individual lighting needs of global brands and OEMs. 3M also offers its full portfolio of light management films, including reflectors, directional films and QDEF. For additional information, contact David Britz, 3M at (651) , dabritz@mmm.com. 5

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