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www. cree.com/xlamp copyright ? 2010 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. CLD-AP70 rev 0 cree/nxp task light reference design cree, inc. 4600 silicon drive durham, nc 27703 usa tel: +1.919.313.5300 application note copyright ? 2011 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 specifca - tion. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. other trademarks, product and company names are the property of their respective owners and do not imply specifc product and/or vendor endorsement, sponsorship or association. introduction this application note demonstrates that an led task light can readily outperform its linear fuorescent equiv - alent and incorporate dimming for mood setting and for additional energy savings. cree, nxp semiconductors and bright view technologies collaborated to design an under-cabinet ssl fxture that exceeds linear fuores - cent performance while keeping cost low and meeting energy star performance specifcations. this design is a simple approach to fuorescent lamp replacement and can easily be integrated into many linear lighting ap - plications. introduction ........................................................ 1 design approach/objectives .................................. 2 the 6-step methodology ....................................... 2 1. defne lighting requirements ........................... 2 2. defne design goals ....................................... 4 3. estimate effciencies ...................................... 4 4. calculate the number of leds needed .............. 5 5. consider all design possibilities ....................... 6 6. complete fnal steps ..................................... 10 conclusions ....................................................... 11 table of contents figure 1 figure 1: nxp cree task light
2 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. design approach/objectives in the cree application note led luminaire design guide, 1 cree advocates a 6-step framework for creating led lu - minaires. all cree reference designs use this framework, and the design guides summary table is reproduced below. step explanation 1. defne lighting requirements ? the design goals can be based either on an existing fxture or on the applications lighting requirements. 2. defne design goals ? specify design goals, which will be based on the applications lighting requirements. ? specify any other goals that will infuence the design, such as special optical or environmental requirements. 3. estimate effciencies of the optical, thermal & electrical systems ? design goals will place constraints on the optical, thermal and electrical systems. ? good estimations of effciencies of each system can be made based on these con - straints. ? the combination of lighting goals and system efficiencies will drive the number of leds needed in the luminaire. 4. calculate the number of leds needed ? based on the design goals and estimated losses, the designer can calculate the number of leds to meet the design goals. 5. consider all design possibilities and choose the best ? with any design, there are many ways to achieve the goals. ? led lighting is a new feld; assumptions that work for conventional lighting sources may not apply. 6. complete fnal steps ? complete circuit board layout. ? test design choices by building a prototype luminaire. ? make sure the design achieves all the design goals. ? use the prototype to further refne the luminaire design. ? record observations and ideas for improvement. the 6-step methodology the major goal for this project was to demonstrate a straightforward task light design using cree xlamp leds that meets or exceeds the performance of a comparison fuorescent fxture. 1. define lighting requirements a desirable task light is low in power consumption and effciently illuminates the area where it is installed. listed in table 1 are specifc metrics that can quantify luminaire performance. 1 led luminaire design guide, application note ap15, www.cree.com/products/pdf/led_luminaire_design_guide.pdf
3 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. importance characteristics units critical luminous fux lumens (lm) luminance/illuminance candela/m2 or lux electrical power watts (w) meet safety standards agency listing/mark price $ lifetime hours important correlated color temperature (cct) kelvin color rendering index (cri) 100 point scale manufacturability $ ease of installation time = $ comply w/energy star has label compatible w/controls yes/no end-of-life disposition cost to recycle table 1: design criteria table 2 summarizes general energy star? requirements to be met to be eligible to qualify for the energy star program. 2 characteristic requirement cct the luminaire must have one of the following designated ccts and fall within the 7-step chromaticity quadrangles as defned in ansi/nema/anslg c78.377-2008. ? 2700 k ? 3000 k ? 3500 k ? 4000 k color angular uniformity the variation of chromaticity shall be within 0.004 from the weighted average point on the cie 1976 (u, v) diagram. color maintenance the change of chromaticity over the frst 6,000 hours of luminaire operation shall be within 0.007 on the cie 1976 (u,v) diagram. cri indoor luminaires shall have a minimum cri of 80. off-state power luminaires shall not draw power in the off state. lumen maintenance requirement l70 > 25,000 hours power factor (pf) total luminaire input power < 5 w: pf > 0.5 total luminaire input power > 5 w: pf > 0.7 warranty 3-year warranty operating frequency > 120 hz table 2: general energy star requirements 2 energy star program requirements product specifcation for luminaires (light fixtures) - eligibility criteria - version 1.0 http://www.energystar.gov/ia/partners/prod_development/new_specs/downloads/luminaires/ es_luminaires_v1_final_specifcation.pdf
4 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. the under-cabinet shelf-mounted lighting requirements 3 : characteristic requirement minimum light output 125 lumens per lineal foot zonal lumen density ? minimum of 60% of total lumens within 0-60 zone ? minimum of 12.5% of total lumens within 60-90 zone minimum luminaire effcacy 29 lm/w table 3: under-cabinet shelf-mounted lighting requirements 2. define design goals the design goals for this project: characteristic unit minimum goal target goal luminaire light output lm 200 300 illuminance/luminance profle lux same better system power w 8 6 luminaire effcacy lm/w 40 50 lifetime hours 25,000 50,000 cct k 3,500 2,700 cri 80 85 maximum ambient temperature c 49 the guiding principle for this design was to meet energy star guidelines and provide an off-the-shelf design that can be used immediately or easily modifed to meet specifc requirements. since it is advantageous to be able to dim a task light, a main goal was to provide ficker-free dimming down to < 1% light output. another goal was to ensure the task light can be switched on at very low dimmer levels. 3. estimate efficiencies of the optical, thermal & electrical systems figure 2 shows basic led electrical data and optical output from crees product characterization tool (pct). 4 we chose a confguration using xp-e leds, and another using mx-6 leds. equally effcient confgurations could be created using xlamp ml-b, ml-e, mx-3 or xp-e hew leds. 3 ibid. 4 available at http://pct.cree.com
5 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. figure 2: cree product characterization tool data 4. calculate the number of leds needed an iterative process was used to determine the number of leds in the task lamp. the initial design used 6 leds at 1.25 in. pitch, but the light uniformity was not suffcient. using fve leds at 1.5 in. pitch, obscured by an precision engineered diffuser and driven at 350 ma, proved to provide optimum illumination. other design choices with larger numbers of lower power leds would be equally plausible. for an extended discussion of led pitch and various optical system trad - eoffs, see cree application note ap34, cree xlamp leds for distributed illumination applications. 5 5 http://www.cree.com/products/pdf/xlamp_distributed_illumination_apps.pdf figure 2
6 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. 5. consider all design possibilities and choose the best designing a solid-state lighting (ssl) linear fxture that exceeds linear fuorescent performance, is cost competitive, and exceeds energy star performance criteria requires a system-level design approach. all four system-level elements, led selection, secondary optics, driver selection/performance and thermal management, must be considered. led selection a linear light fxture is expected to provide uni - form light transmission, color temperature and, in the case of a dimmable led-based fxture, main - tain color temperature while dimming. this design shows that both the cree xlamp xp-e and mx-6 leds exceed the targets for this application. the xp-e led can be driven at a much higher current than the mx-6 led, producing more light within the fxture, if requirements dictate. led placement within the fxture is also critical. linear fuorescent lamps have uniform light trans - mission and are omnidirectional. this gives a nice lighting profle when looking directly at the fxture, but also comes with a performance penalty in the constrained space of undercabinet design. since ssl luminaires are point sources, careful consideration of led place - ment within the fxture is vital. secondary optics the diffuser in the comparison linear fuorescent fxture traps as much as 50% of the light produced by the fuorescent tube. this has a huge negative impact on total effcacy of the fxture. working with bright view technologies 6 , a linear diffuser was designed and optimized for this application. this allowed for almost 85% of the light generated by the leds to be transmitted through the diffuser and onto the work surface. luminous flux cct cri ssl without diffuser 307 lm 4051 85 ssl with diffuser 261 lm 4033 85 table 4: performance of led task light vs. linear fuorescent 6 www.brightviewtechnologies.com figure 3 figure 3: xp-e led figure 4 figure 4: ml-e led figure 5 figure 5: mx-6 led figure 6 figure 6: xp-e hew led
7 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. to eliminate shadowing and produce light uniformity, the led-to-diffuser distance had to be tailored so the point-source leds are essentially invisible. the original design placed the leds 0.75 in. behind the diffuser. though bright view worked to optimize the diffuser, the distance between the leds and from the leds to the diffuser produced a suboptimal result, with the individual leds clearly visible and corresponding shadowing apparent. a second design placed the leds 1.75 in. behind the diffuser. the end result was a task light that has little to no shadowing from end-to-end of the fxture and hides the leds so the point sources are eliminated. driver topology and performance it is highly likely that a user will come in contact with the fxture, so a safe topology that isolates the user from the ac mains is required. one of the great features of the ssl2101 7 is its ability to be confgured for both buck (non-isolated) and fyback (isolated) confgurations. we selected the fyback topology for this design, providing the maximum safety available in an ssl fxture. driver effciency is critical, and this design achieves 80% effciency at full load, as shown in figure 7 and figure 8. figure 9 shows the power factor. the curves in these fgures are for three drivers tested under identical conditions. differences in the curves are due to variances in the driver performance based on manufacturing/component spreads in the driver assemblies. figure 7: ssl2101 driver effciency without triac dimmer in the circuit 7 http://www.nxp.com/#/pip/pip=[pip=ssl2101]|pp=[t=pip,i=ssl2101] figure 7 75.00% 77.00% 79.00% 81.00% 83.00% 85.00% 80 100 120 140 efficiency (%) input voltage (v) #1 #2 #3
8 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. figure 8: ssl2101 driver effciency with triac dimmer in the circuit at maximum lumen output figure 9: power factor without triac dimmer in the circuit using the ssl2101 enabled a sought-after feature, triac dim - ming, to be provided. one of the main design goals was to be able to dim the task light down to < 1% light output without fick - ering. since the nxp ssl drivers are specifcally designed with this in mind, the goal was achieved with a straightforward design. another goal was to ensure a user can switch on the task light at very low dimmer levels. the low voltage startup of the ssl2101 made this achievable. figure 8 75.00% 77.00% 79.00% 81.00% 83.00% 85.00% 80 90 100 110 120 130 140 efficiency (%) input voltage (v) #1 #2 #3 figure 9 0.840 0.870 0.900 0.930 0.960 0.990 80 100 120 140 pf input voltage (v) #1 #2 #3 figure 10 figure 10: ssl2101
9 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. thermal management thermal management is critical in ssl luminaires. ensuring the recommended maximum led junction temperature is not exceeded is critical to long life and color point stability of the leds. we designed an aluminum housing, increasing the housing cost by 30% over a sheet metal version. this increased cost was offset by improved thermal performance without the necessity of an additional heat sink. an aluminum housing allows the led assembly to be produced with standard fr-4 pcb material. thermal images of the led board show that the system is well below the recommended maximum operating tempera - tures of the components in the design. figure 11 shows a thermal view of the led area of the led task light. the temperature/time chart plots the maximum temperature in the led area versus time figure 11: thermal view of led task light figure 11 C part 1 figure 11 C part 2
10 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. task light design the led task light utilizes fve cree xp-e or mx-6 leds driven by the nxp ssl2101 driver. the leds are a great ft in linear applications and feature an electrically isolated thermal path, enabling heat removal through low-cost pcbs, and excellent color point stability, all with industry-leading lumen maintenance. the design utilizes nxps ssl210x triac dimmable driver family to achieve excellent deep dimming, isolated fyback design, ease of mechanical design and excellent effciency, approximately 79%, all with a pf > 0.9. this, in conjunction with crees superb lighting class xp-e or mx-6 leds, offers lighting designers a new standard in led lighting. the output is set at 6 w and delivers approximately 307 lumens without the diffuser. with the bright view diffuser, the task light produces approximately 261 lumens. the equivalent fuorescent light had a lumen output through the diffuser of 201 lumens for 8 w of power. 6. complete final steps performance summary table 5 compares the performance the led task light to a linear fuorescent. the led task light produces 25% more lumens for 25% less power (6 w vs. 8 w) and has a signifcantly better cri than the fuorescent. these tremendous results are achieved using state of the art cree xp-e or mx-6 leds coupled with nxps triac dimmable ssl2101 driver, capable of dimming the led fxture down to < 1% of light output completely fick er free. luminous flux cct cri led task light 261 lm 4033 85 fluorescent task light 201 lm 4068 62 table 5: performance summary of led task light vs. linear fuorescent the led task light boasts triac dimming capabilities that the comparison fuo - rescent fxture lacked. the dimming is smooth and ficker free down to < 1% of light output and the unit can be switched on at very low light output levels. the unit is compatible with a wide range of off-the-shelf triac dimmers from popular manufacturers including lutron, leviton and cooper. the basic design of this 6-w led task light can be adapted quite easily for any type of 5-12 w led fxture. figure 12 figure 12: various triac dimmers
11 nxp cree task light reference design copyright ? 2011 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 specifcation. for product specifcations, please see the data sheets available at www.cree.com. for warranty information, please contact cree sales at sales@cree.com. conclusions this led task light readily outperforms a fuorescent equivalent. with good design practice we have shown how thermal performance can be managed for a long lifetime design. the completely ficker-free deep triac dimming brings another dimension to the fxture compared to fuorescent equivalents. using industry-leading cree lighting class leds and nxps driver, the fexible design can be applied as is or modifed to different mechanical formats for multiple applications, such as an led downlight or a wall-washing fxture. if more light is required, the power level of the design can be easily modifed up to 15 w using the ssl2101 driver and up to 25 w using the ssl2102. this fexibility, coupled with brighter or more cree leds, can accommodate most applications.

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