3M Optical Systems Division LED Backlights Made Simple 3M Integrated Optics for LCD by: John Wheatley, 3M Optical Systems Division Power that Changes the World
Contents Executive Summary...4 Architecture Overview A Comparison...4 How Works...5 Key Feature Comparison...6 Eliminates Prisms and the Problems They Create...7 Eliminates Prisms and the Problems They Create...9 Quantifying the Value of Integration Factory Floor Simulation...10 A Major Improvement in Environmental Impact of Backlights...11 Conclusion...11 Recap: 3M Advantages...13 Our Vision Integrated Optics for All Displays...13 About 3M...14 References...15 33
Executive Summary LED Backlights Made Simple LED backlights are now used in all sizes of LCDs. They are thin and sleek, and the industry has an installed manufacturing base that allows them to be made by the millions for a host of applications, from smart phones, tablets, and laptops to monitors, televisions and signs. Their key drawbacks are that they are much more complex and costly than they need to be, and they needlessly generate many millions of pounds of plastic waste every year, compared to the alternative. This paper discusses that alternative: 3M is a radically simple approach for LED backlights based on a recent advance from 3M. Unlike today s backlights which require multiple films to diffuse, collimate, and polarize light combines all functions in a single film. The film is also very compatible with the industry s installed manufacturing base; it is placed in the backlight as a free-floating film during assembly, in the same way that current films are applied. Since conventional backlights use 3 4 separate films, the use of 3M greatly reduces the number of components, assembly time, thickness, weight, and waste. It also simplifies and shortens the supply chain and reduces inventory and the labor required for assembly. From a performance standpoint, is comparable to conventional systems (as measured by Nits/W) and exceeds conventional systems in wide-angle luminance a benefit of particular importance in TVs and LCD signage, and devices where a shared viewing experience is key. also allows manufacturers to eliminate one or more prism films; this enhances the viewing experience by allowing a monotonic (i.e., a smoothly and gradually decreasing) change of luminance as the viewing angle changes. This effect is difficult to achieve with prism films, which tend to cause abrupt changes in luminance. Our experience is that viewers prefer displays with over conventional displays. We attribute this preference to the improved wide-angle luminance and the monotonic change in luminance. In addition to these cost and performance advantages, allows display manufacturers to make a notable indeed, remarkable improvement in the environmental profile of their products. It allows manufacturers to eliminate some 70 million pounds of plastic from the industry waste stream annually. As a result, provides multiple opportunities for cost reduction, from material costs to the simplification of design, inspection, and assembly. Architecture Overview A Comparison A conventional LCD backlight architecture is shown on the left of Illustration 1. It consists of a back reflector mounted on the chassis, followed by a solid light guide, one or more diffuser and prism films, and a reflective polarizer. The final element is the LCD panel. Traditional Display Architecture Reflective Polarizer LEDs Diffuser Reflector/ Chassis Display with The architecture is on the right. It consists of a single film, a light guide and conventional white back reflector mounted on the chassis. All other films the diffuser film(s), prism film(s), and the reflective polarizer are eliminated. LCD Panel Prism/ microlens Light Guide Illustration 1 Traditional Multi-film and New Single Film Backlight 4
How Works Light Guide Illustration 2 3M s angle-selective optics provide collimated polarized light. is based on 3M s new Collimating Multilayer Optical Film (CMOF) technology, which enables a new class of optical film that provides the functionality of a diffuser, a prism/microlens film, and a reflective polarizer 1-3. As a result, for the first time, LCDs with highly integrated optics are possible with a single free-floating film. Rather than refracting, collimates light by preferentially reflecting higher angle light back to the recycling cavity, while providing higher transmission for light closer to normal incidence. Wide-angle luminance and system level efficiencies are comparable to or exceed those of conventional multi-film backlights as shown in later examples. is based on 3M s Multilayer Optical Film technology, which brought products such as 3M DBEF and 3M APF to the LCD industry. Illustration 3 3M s Multilayer Optical Film technology, featured in the journal Science 4 5
Key Feature Comparison Category Conventional ( BD/Crossed Prism) Number of free floating components 3 4 1 Assembly steps 3 4 1 Labor X 0.3X On-axis brightness Similar Similar Total light output X 1.55X Table1 Key feature comparison, conventional vs. backlights 8.0 Display Efficacy (Nits/W) 7.5 7.0 6.5 6.0 Beaded Diffuser/Crossed Prism Microlens/Prism/Cover Sheet 25 30 35 40 45 50 Horizontal Half Luminance Angle (degrees) Illustration 4. Efficacy vs. Half Luminance angle for and traditional multi-film stacks, showing has both a broad viewing angle and a display efficacy that compares favorably to conventional systems. 6
Eliminates Prisms and the Problems They Create Prism films have been used for years in displays but cause many compromises in system design and cost. They also affect certain performance characteristics, including wide-angle luminance. Specifically, prisms typically cause abrupt changes in brightness as a function of viewing angle, as shown in Illustration 5. 3 Film Stack Beaded Diffuser/xPrism Illustration 5 Luminance conoscopic plot comparison of 3-film stack and showing that provides a much broader viewing angle with similar on-axis brightness. Note in Illustration 6 how smooth and monotonic the viewing angle is compared to the crossed prism films. provides a superior viewing experience and 55% more total light output. Recent scientific studies have shown a significant consumer preference for broad viewing angle displays. 5 Illustration 6 Angular luminance detail showing monotonic characteristics of 3M vs. crossed prism films, which is abrupt and has inversion. 77
In addition to luminance fall-off, prisms cause many other issues affecting display quality and cost (Table 2). For example, prisms can be damaged or cause damage to other optical components (including the LCD panel) in assembly, transit, or use. Also, their periodic structure and geometry can create spatial interference patterns (moiré) and color mura, imposing constraints on the choice of panel type or other backlight films. This can introduce costly complications such as the need to introduce a bias (in-plane rotation) of the film in order to minimize these effects. Particularly in mobile devices, the need to pair appropriate panel pixel pitch to prism pitch severely limits design flexibility, development speed, and part yield. It also causes a substantial proliferation of parts (SKUs). Table 2 below summarizes these and other issues. 6 Table 2 Prism Related Issues 8
A Radical Simplification of the LCD Supply Chain 3M creates significant opportunities for improving the efficiency of LCD manufacturing. The top schematic of Illustration 7 shows the current LCD supply chain with a focus on the backlight materials. Today, three to four different components are supplied to the OEM. For each there are multiple steps including raw material manufacture, yielded material losses in article fabrication, packaging, and energy used for transportation by land, sea, and air. In contrast, greatly streamlines the overall process; it reduces steps, costs and waste. Supply Chain Today Multiple materials, inspections, assembly steps, waste sources Panel Makers Cover Sheet Converting Integrators Brands Retailers Consumers Prism/mLens Converting Microlens Converting Cover Sheet Fabrication Prism/mLens Fabrication Microlens Fabrication Cover Sheet Materials Prism/mLens Materials Microlens Materials Material Suppliers New Supply Chain Streamlined, minimal materials, minimal steps Panel Makers Integrators Brands Retailers Consumers Converting Fabrication Materials Illustration 7 Supply chain efficiencies, conventional vs. backlights 9
Quantifying the Value of Integration Factory Floor Simulation A process simulation of a display factory compared to a conventional three-film factory is shown in Illustration 8. 7 We chose what we felt were a reasonable set of assumptions for operators, assembly steps and times, scrap and reject rates. Though each factory is unique, the results clearly indicate that large improvements in throughput, scrap, and labor efficiency are possible. This represents many opportunities for cost reduction. 3M works with customers to apply this type of analysis to specific situations and metrics of interest. 10 Illustration 8 Factory Floor Model of vs. Traditional Factory
A Major Improvement in Environmental Impact of Backlights The resulting material reduction can be dramatic. We estimate that changing from a multi-film system to could reduce waste by approximately 70%. For the industry as a whole, this means approximately 70 million pounds (32 million kg) of plastic could be eliminated (Illustration 9). Illustration 9 Industry-wide material reduction potential with 8-9 Conclusion It is now possible to make LCD backlights using only one free-floating film. This enables multiple cost-down, best-in-class system value propositions including: fewest parts, thinnest, lightest weight, and lowest amount of material (Illustration 10). Integration, as shown here with, provides simplification in all aspects from product design to supply chain to the factory floor. This presents a rare opportunity to provide new value propositions to consumers and to make non-incremental advancements in the environmental profile of LCD display technology. 11
12 Illustration 10 3M simplifies all aspects of product development and manufacturing, from product design to supply chain to the factory floor.
Recap: 3M Advantages Cost reduction Fewer components, fewer inspection steps, streamlined factory floor and supply chain operations. Waste stream reduction Cuts the amount of plastic used for optical films by up to 70%. Robustness Energy efficiency Broad luminance angle Prism-related issues such as moiré and rainbow mura are eliminated. ENERGY STAR compatible. Suitable for monitor, TV, signage, or mobile devices. Monotonic luminance angle A noticeably superior viewing experience. Scalable Manufacturing flexibility No change in backlight assembly method For all size displays. can be used on multiple types and sizes of displays. Assembly time is reduced. backlight assembly is done in the traditional way. Number of SKUs The inspection, handling, waste, and assembly of multiple films is reduced by as much as 75%. Thickness reduction Weight reduction Display thickness can be reduced due to elimination of several films and their respective z-gaps. Removal of several free-floating films reduces weight by about one pound (454 g) in a 52" TV. Our Vision Integrated Optics for All Displays New Integrated Optics Architectures Conventional Backlight Architecture LCD Panel Prism/ microlens Light Guide Box/ Chassis On-Panel for Edge-Lit 3M has a portfolio of solutions to enable the industry to realize the benefits of integrated optics. These include the free-floating, as well as on-panel integration for direct and edge-lit systems (Illustration 11). For more information please contact 3M Optical Systems Division. Reflective Polarizer Diffuser Reflector On-Panel for Direct-lit Illustration 11 The 3M Portfolio of Solutions for LCD Integrated Optics 13
About 3M 3M is a member of the Sustainability Consortium Electronics Sector Working Group. The Sustainability Consortium is an independent organization of diverse global participants who work collaboratively to build a scientific foundation that drives innovation to improve consumer product sustainability through all stages of a product s life cycle. The Sustainability Consortium develops transparent methodologies, tools and strategies to drive a new generation of products and supply networks that address environmental, social and economic imperatives. 10 14
References 1. T. Liu et. al., SID 09 Digest, 55.1, Edge-lit Hollow Backlight Using Tunable Reflective Polarizer for LCD Displays. 2. J. Wheatley et. al., Optics Express, Vol. 17, 2009, Efficient LED Light Distribution Cavities using Low Loss, Angle-Selective Interference Transflectors. 3. J. Wheatley et. al, SID 11 Digest, 60.1, LCD Integrated Optics. 4. M. Weber, et. al., Science, March 2000: Vol. 287 no. 5462 pp. 2451-2456. 5. 3M White Paper on Broad Viewing Angle, 2012. 6. J. Wheatley et. al., SID 12 Digest, Invited Paper, Greener Displays through Integrated Optics: Display Backlights using. 7. Lanner Witness software, Forward House, 17 High Street, Henley-in-Arden, Warwickshire, B95 %AA, UK. 8. Seung-Jin Lee and Joyce Cooper, Estimating Regional Material Flows for LCDs, Proceedings of the IEEE International Symposium on Electronics and the Environment ISEE (May 2008). 9. 3M White Papers on Sustainability, 2011-2012. 10. The Sustainability Consortium, www.sustainabilityconsortium.org. John Wheatley, Division Scientist, 3M Optical Systems Division, jwheatley1@mmm.com. 15
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