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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®conferences | SIL EUROPECFL and high-pressure sodium (HPS) lightsources. The greatest energy savings areassociated with using LEDs and appropriatedimming levels. As a comparison, HPSsources can only be dimmed to approximately40% of their maximum lumen outputand system efficacy is compromised withall levels of dimming (Fig. 4). In other words,higher input power is required to producethe same lumen output. For example, a 60WCosmo luminaire with Harvard DALI ballastat a 50% light-output level requires approximately67% of input power.System efficacy is better with CFLs, wherehigh efficacy is maintained down to about40% lumen output levels. For a typical fixture,30% lumen output requires approximately35% input power. However, below a40% dimming level, CFLs suffers from cathodeand driver inefficiencies.LEDs are easier to dim and hypotheticallycan be dimmed readily to as low as1%. System efficacy is excellent from 100%LM-80 / LM-79 TEST SERVICESSetting the Standard for LED MeasurementORBoptronix>DဒϬ>DϳဓdĞƐƟŶŐ^ĞƌǀŝĐĞƐKƌďKƉƚƌŽŶŝdžŝƐƚŚĞĮƌƐƚŝŶĚĞƉĞŶĚĞŶƚϯ ƌĚ ƉĂƌƚLJ/^KϭϳϬϮϱĐĐƌĞĚŝƚĞĚh^>ĂďŽƌĂƚŽƌLJŽīĞƌŝŶŐĐŽŵƉůĞƚĞ>DဒϬ>ƵŵĞŶDĂŝŶƚĞŶĂŶĐĞdĞƐƟŶŐEZ'z^dZWZĞĐŽŐŶŝnjĞĚK>ŝWZ^^>>ƵŵŝŶĂŝƌĞdĞƐƟŶŐĚĚŝƟŽŶĂů^ĞƌǀŝĐĞƐ>LJĞ^ĂĨĞƚLJǀĂůWƌŽĚƵĐƚdĞƐƟŶŐĨŽƌZŝƐŬ'ƌŽƵƉůĂƐƐŝĮĐĂƟŽŶdK>ŚĂƌĂĐƚĞƌŝnjĂƟŽŶ^ĞƌǀŝĐĞETO-S20-P6-HPAETO-TEC-100to around 20% of light output. For instance,a 50W-equivalent luminaire with Harvard700 mA DALI driver at 50% light outputonly requires 44% input power. With currenttechnology, system efficacy becomesimpacted by driver efficiency below 20% oflight output.According to Khan, simple analogswitch dimming (0-10V) works well on asmall scale, but requires too much cable forlarge-scale implementations. More expensivecontrol options such as DALI can providegreatwer flexibility for projects of allsizes and are re-configurable. However,DALI and other approaches require furtherwork to fully maximize control efficiencyand power factor over the control range.Ultimately, Khan expects the industry tomove to wireless intelligent control systemscapable of plug-and-play operation.Also in the drivers session, Steve Roberts,technical manager at Recom, Austria,discussed the significant impact that&RPSOHWH6(59,&(6&RPSOHWH6ŚĂƌĂĐƚĞƌŝnjĂƟŽŶ^LJƐƚĞŵƐddĞŵƉŽŶƚƌŽůǁŝƚŚdƐdĐdũDŽŶŝƚŽƌŝŶŐ,ŝŐŚůLJĐĐƵƌĂƚĞ>^ƉĞĐƚƌĂů&ůƵdžDĞĂƐƵƌĞŵĞŶƚƐĂŶĚWtDWŽǁĞƌ^ƵƉƉůLJŽŶƚƌŽůƐE/^ddƌĂĐĞĂďůĞůĞĐƚƌŝĐĂůdŚĞƌŵĂůKƉƟĐĂůĂƚĂƵƚŽŵĂƚĞĚĂƚĂĐƋƵŝƐŝƟŽŶĂŶĚŶĂůLJƐŝƐdŽŽůƐϰtŝƌĞsŽůƚĂŐĞĂŶĚƵƌƌĞŶƚDĞĂƐƵƌĞŵĞŶƚƐ,ĂƌĚǁĂƌĞ^ŽůƵƚŝŽŶƐŝŶĐůƵĚŝŶŐZĞƚƌŽĨŝƚŽƌƵƐƚŽŵ25%237521,;,1&6DOHV#2UE2SWURQL[FRP3OHDVHYLVLW2UE2SWURQL[FRPIRUDIXOOOLVWRISURGXFWV _____________VHUYLFHVhigh temperature can have on luminairereliability. He made several design recommendationsfor minimizing temperatureincreases in LED luminaires includingmounting the LEDs so that they havelow thermal impedance to the heat sinkand mounting the driver away from theLEDs and heat sink. The heat sink shouldbe designed for the most efficient size/efficiencyratio. Thermal derating can be usedto reduce the LED current if the junctiontemperature approaches specification limits.Roberts further recommends limitingthermal cycling and allowing for a singleLED failure in multiple LED installations.Input-output voltage transients can bemanaged by using spike protection as wellas short input cables with relatively-longeroutput cables.Regarding triac dimmers, Roberts recommendsthat engineers consider the timingof triggers and the effect on the driverelectronics. Rather than separate AC/DCballasts, a centralized DC-power-distributionapproach should be used with a largeAC/DC power supply feeding multiple DC/DC LED drivers. Finally, Roberts recommendsconsideration of the reliability ofevery component in the luminaire system.Designing power-distribution networksA presentation by Marc Ottolini of iSoteraLtd of Hoddesdon, UK, considered the utilityof DC-power-distribution networks forSSL. Ottolini compared four scenarios –the legacy architecture, a centralized DCStar approach where one AC/DC supplyfeeds DC/DC drivers, a DC grid where lowvoltageDC leaves the AC/DC supply, or acentralized high-frequency AC (HFAC) busapproach. For each approach, he looked atsimplicity of installation, cost, safety, reliabilityand controllability.He concluded that there is no compellingbenefit to implementing a full-DC-powerdistributionsystem for LED lighting. However,a centralized (bulk) power processingapproach can be advantageous if up anddown (2-stage) conversion can be made efficientenough, which depends on the diversityof the LED load. He finalized with thestatement that energy-efficiency benefitsalone (2-5%) do not provide enough impetusto begin setting new standards.34 NOVEMBER/DECEMBER 2011 LEDsmagazine.comPrevious Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM qMM MQmags| Next Page q qTHE WORLD’S NEWSSTAND ®