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LED Color Mixing: Basics and Background CLD-AP38 REV 0A REV CLD-AP38 TECHNICAL ARTICLE LED Color Mixing: Basics and Background INTRODUCTION TABLE OF CONTENTS This technical article explains a few approaches to The Need for Color Consistency ............................ 2 creating color-consistent, LED-based illumination The Basic Approaches ..................................... 4 products and guides readers in how to work effectively Led Binning ....................................................... 4 with Cree products to achieve this goal. Chromaticity Bins ........................................... 4 Flux Bins ....................................................... 6 LEDs, as with all semiconductor devices, have Using Colorimetry and Binning Information in material and process variation which yields product Illumination Specification ..................................... 7 with corresponding variation in performance. LEDs Three Approaches ............................................... 9 are binned and packaged to balance the nature of Buy Single (or Few) Chromaticity Bins ............... 9 manufacturing process with the needs of the lighting Use Cree EasyWhite Parts .............................. 10 industry. Lighting-class LED products are driven Do Color Mixing in the LED System ................. 10 by the needs of the solid-state-lighting industry, Cree’s Color Mixing Tool, the Binonator ............ 14 application requirements and industry standards, Conclusions ..................................................... 18 including color consistency, as well as color and lumen Appendix: Colorimetry and Binning Basics ........... 19 maintenance. Color-Space Basics ....................................... 20 Idealized Illumination Colors .......................... 22 McAdam Ellipses ........................................... 24 Partitioning the Color Space – Binning ............. 26 Summary .................................................... 29 P M LA OM/X C . CREE Copyright © 2010-2012 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, Inc. Cree, the Cree logo and XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes 4600 Silicon Drive only and is not a warranty or a specification. For product specifications, please see the data sheets available at www.cree.com. Durham, NC 27703 WWW. WWW. For warranty information, please contact Cree Sales at [email protected]. USA Tel: +1.919.313.5300 LED COLOR MIXING THE NEED FigureFOR COLOR 1: The CONSISTENCY Need for INColor LED IConsistencyLLUMINATION Spans all Illumination There is nothing like a picture to illustrate the needTechnologies for every illumination technology to deliver consistent color. It is an example of the problem we are trying to solve. Figure 1: The need for color consistency spans all illumination technologies1 Though this illustration is from an array of HID lamps illuminating the facade of a building, it shows the undesirable results of inconsistent color in manufacture and color maintenance of luminaires as they age. An increasingly active industrial policy in the United States, European Union and throughout the world, is resulting in a rigorous set of performance requirements for LED lighting applications. For example, the 2010 document “ENERGY STAR® Program Requirements for Integral LED Lamps”2 proposes stringent requirements, significantly above those for CFLs,3 the first industrial policy mandated illumination technology. The LED Lamp requirements were preceded by the 2008 document “ENERGY STAR Program Requirements for Solid State Lighting Luminaires.”4 In each of these documents, there are requirements in CCT, CRI, lumen and color maintenance for an Energy Star-approved LED illumination product, excerpted in Tables 1 and 2 below. 1 Picture: Taken from “The Roof,” The Wit Hotel, Chicago (Courtesy of Osram) 2 www.energystar.gov/ia/partners/manuf_res/downloads/IntegralLampsFINAL.pdf 3 See www.energystar.gov/ia/partners/prod_development/revisions/downloads/cfls/Criteria_CFLs_V4.pdf 4 www.energystar.gov/ia/partners/product_specs/program_reqs/SSL_prog_req_V1.1.pdf Copyright © 2010-2012 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at [email protected]. 2 LED COLOR MIXING Table 1: Energy Star requirements for Integral LED lamps, per program requirements (V1.1) Table 2: Energy Star requirements for LED Luminaires, per program requirements (V1.1) These requirements highlight the need to achieve defined, repeatable results with the manufacturing output the LED supplier. Copyright © 2010-2012 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at [email protected]. 3 LED COLOR MIXING The Basic Approaches There are three ways in which a company can work with Cree to procure LEDs to achieve color-consistent lighting products: 1. Buy one, or a very small number of bins. The purchase of the same small collection of parts over and over is a reasonable and repeatable strategy, but due to nature of LED manufacture this is never the lowest cost way to procure a production supply of LEDs. 2. With the release of EasyWhite™ products, beginning in late-2009, Cree has made it possible for its customers to work with LEDs in a way that is similar to original bulb-specification practices, e.g., specifying just CCT and flux. Cree performs color mixing on behalf of its customers in building EasyWhite versions of the XLamp MC-E or MP-L LEDs. 3. Traditionally the most cost-effective way to work with Cree is to buy full distributions of XLamp LEDs, that is, the full manufacturing output of an LED production run, which includes variety in flux and chromaticity. In order to use full distributions effectively, the customer develops expertise in multi-LED illumination systems and color-mixing recipes. Color-mixing recipes offer flexible and multiple solutions to create repeatable chromaticity results and can deliver a cost-competitive advantage over the first two approaches. The rest of this document gives a framework and set of tools for those who want to do color-mixing in their own multi- LED illumination products. LED BINNING LEDs can be characterized in multiple ways. For color mixing, the two most important dimensions are color and flux. These parameters are collected as part of the LED component manufacturing process and are the basis for the component binning discussed in this document. Copyright © 2010-2012 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at [email protected]. 4 LED COLOR MIXING Chromaticity Bins Cree provides industry leading granularity by defining sub-bins within each of the ANSI C78.377 bins for warm, neutral and cool white XLampFigure products. 2: XLamp Warm and Neutral White Bins Figure 2: XLamp warm- and neutral-white bins Each product family has a binning and labeling document which provides the necessary specification to order Cree LED components. URLs to some of these documents on the Cree website are shown below. Cree® XLamp® XP Family LED Binning and Labeling, CLD-AP22 www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20 Binning/XLampXPBL.pdf Cree® XLamp® MX Family LED Binning and Labeling, CLD-AP30 www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20 Binning/XLampMX_BL.pdf Cree® XLamp® MC-E LED Binning and Labeling, CLD-AP20 www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/Data%20and%20 Binning/XLampMCE_BL.pdf Copyright © 2010-2012 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at [email protected]. 5 LED COLOR MIXING Chromaticity Bins (Continued) Beginning in December 2009, Cree launched a version of a multi-die LED component, the XLamp MC-E EasyWhite™. A second multi-die member of the EasyWhite binning family was announced with launch of the XLamp MP-L EasyWhite. EasyWhite represents a significant simplification of the progression of multiplying LED bins as the map below shows. Instead of dozens of chromaticity bins,Figure there is only 3: one EasyWhitechromaticity bin for eachBins standard color temperature. This approach is also unique in that each of the four bins are centered on the Black Body Line. 0.45
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