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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®lighting | PLANAR FIXTURESfor edge-lit fixtures can produce good uniformity,but they have a wide range of opticalefficiencies, tooling costs, manufacturingcosts, and optical characteristics.Printed and chemically-etched dots offerlow-cost manufacturability, but producediffused light outputs that offer virtually nocontrol of the beam pattern. Laser-etchedoptical features provide improved opticalefficiency, but require long manufacturingcycle times. Light guides with embeddedoptics combine specular reflection withfast and highly-repeatable manufacturingto deliver the highest level of ray-angle controland lowest overall cost.One example of embedded optics is Rambus’MicroLens light-distribution technology.MicroLens optics are 3-dimensionalelements embedded directly into the lightguide using injection molding, extrusion,or hot-embossing processes. They producea highly-directed light output, provide rayanglecontrol, and maximize the amountof light delivered on target. In addition, thedistribution pattern can be customized tomeet specific application needs by varyingthe shape, size, location and densityof the optics.In many ways, edge-lit architectures combinethe benefits of direct and indirect fixtureswhile also providing unique benefits.They offer high optical efficiency, control ofthe light distribution, reduced number ofLEDs, and superior aesthetics. The adoptionof edge-lit BLUs has enabled sleek, ultrathinnotebook computers, tablets, monitorsand HDTVs that are less than 0.3 inchthick at a lower cost than direct-lit counterparts. Those same benefits can be leveragedfor lighting. Light guides with embeddedoptics can be implemented in countlessshapes and sizes with a wide variation oflight distribution patterns. Edge-lit fixtureswill usher in a new era of efficient, flexibleand beautiful products. But with these newcapabilities and flexibility of form factor,what is the best method for comparing relativeperformance and efficiency?Introducing a new metricWith the introduction of energy-efficientlight sources, such as fluorescents andLEDs, the reference to the wattage of a bulbis no longer an acceptable means of expressingthe light output. In an effort to ease theIn many ways, edge-lit architectures combinethe benefi ts of direct and indirect fi xtureswhile also providing unique benefi ts.PatterningtechnologyMethodOpticsOpticalefficiencyUniformityManufacturabilityPrinted dot Diffuse Good Good FastChemicaletch Diffuse Good Good FastFIG. 2. Optical elements can be formed in several ways.transition, the term "watt equivalent" hasbeen used to provide a reference. For example,a typical 60W incandescent bulb generatesabout 800 lm. But a 60W-equivalentLED bulb uses less than 12W to produce thesame amount of light. The use of lumens hasalso been incorporated to describe the luminousflux or light output of a light source.Luminous efficacy, measured in lumens-perwatt(lm/W), is an important metric whendescribing the efficiency of a light fixture,but it doesn’t tell the whole story.Lumen output provides an accurate representationof traditional light sources as it isan averaged value used to measure total lightoutput from an omnidirectional light source.However, LEDs are directional, so these metricsfail to accurately depict the true benefitsof LEDs as general light sources. By usinglumen output as a measurement for LEDbasedfixtures, the actual amount of light theluminaire is capable of delivering to a specificsurface can be misrepresented.Where all of these metrics miss the mark isthat they measure the amount of light emittedfrom a light fixture rather than the actualamount delivered to the desired applicationarea. The end goal of any lighting design isto create beautiful, functional spaces as efficientlyas possible. This is achieved throughthe uniform distribution of light to a desiredsurface, minimizing light lost in undesireddirections, and improving lighting ergonomicsthrough reduced glare.Application efficiencyIn order to truly maximize the amount oflight delivered to a desired area with theleast amount of energy required, designersmust focus on the application efficiencyof the fixture. Application efficiency is thepercentage of light delivered to the targetedarea as it relates to the total light output ofthe fixture. In other words, the amount oflight emitted from a fixture and directed toa specific surface. In order to achieve highapplication efficiency, a fixture must combinehigh luminous efficacy with the abilityto direct as much of the emitted light to thedesired surface, or area, as possible (Fig. 3.).Application efficiency depends on threeLaser etch Diffuse Better Better Slow Specular(ray angle control) Best Best FastEmbeddedoptics62 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 ®
Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®lighting | PLANAR FIXTURESOptimizedLED-to-light-guideinterfaceCustom controlledlight outputMaximum lightextractedfrom light guideHigh opticalefficiency+ =Precise rayangle controlHighestapplication efficiencyFIG. 3. LEDs and ray control yield high application effi ciency.elements: the efficacy of the LEDs, the opticalefficiency of the total fixture, and thedegree of ray-angle control provided bythe fixture’s optics. Today’s high-brightnessLEDs deliver upwards of 140 lm/W,but not all of the light emitted from theLEDs is effectively delivered to the fixture.Special design techniques are requiredin order to maximize the efficiency of theinterface between the LED light source andthe light guide.There are additional losses introducedby the fixture inherent in the LED driverused to condition the power supplied tothe LEDs, the thermal-management systemused to cool the fixture, and the opticsused to extract light out of the fixture. Asystem-design approach which takes allof these elements into account is requiredto maximize the overall efficiency of thelight fixture.Finally, light emitted by the fixture inundesired directions is effectively lost. Theability to control the light delivered fromthe fixture to the desired area depends onthe nature of the optics used in the lightguide. While diffuse optics cannot directthe light in a specific direction, specularoptics embedded in the light guide, suchas MicroLens optics, can. As a result, morelight can be directed to the desired surface,with less light straying to an unneeded area.A system approachBy optimizing the LED efficacy, opticalefficiency, and driver design, and then providingray-angle control, fixture designerscan achieve maximum application efficiencyto reach their end goal of creating aproductive, functional space with the leastamount energy.In the display market, edge-lit architecturesare the leading way to employ LEDsfor BLUs. They deliver efficiency, thin displays,and low cost. Ultimately, these samebenefits will translate to edge-lit architecturesbecoming the preferred solutions forlighting. The added benefit of form-factorflexibility means edge-lit solutions offertremendous freedom of design. Lightingdesigners no longer need be constrainedby the limitations of legacy bulb and tubebasedfixtures. Nor should they evaluatelighting solutions only in terms of legacymeasures. By designing with maximumapplication efficiency in mind, they can createbeautiful, functional spaces with fewerfixtures and lower energy consumption._______________LEDsmagazine.com NOVEMBER/DECEMBER 2011 63Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM qMM MQmags| Next Page q qTHE WORLD’S NEWSSTAND ®
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