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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | SubscribeqMqM | Next PageqqM qMMQmagsTHE WORLD’S NEWSSTAND ®conferences | SIL EUROPEmay permeate the silicone dome. Light exposurecauses the VOCs to oxidize, creating adiscoloration of the silicone. If, instead, theLED emitters are not contained in an airtightenvironment, VOCs have a chance todiffuse out and not interfere with the opticaltransmission.The importance of visual comfort with LEDluminaires was also emphasized by GiorgiaTordini, an optical designer with Philips ProfessionalLighting Solutions, who presented“The visual barrier: Designing the nightappearance of an LED product.” She definednight appearance as a person's visual perceptionwhen a light is first switched on in itsapplication. Very high luminance from LEDlight (108 cd/m²) can cause glare, which is anuncomfortable reaction to brightness. Tordininoted that glare is different from photobiologicaldamage, which is caused mainly bylight in the UV realm.Tordini described the optical system ofPhilips’ DayZone luminaire for office lighting,which has a task light in the middle anda separately-controlled outer ring-light forambient lighting. The luminance of the outerring is 3x smaller than that of the inner portion.The luminance limit for work spaces,according to British Standard EN-12464,is 1000 cd/m² at a 90-degree to 65-degreeangle from the vertical axis.Tordini explained that the optical designuses primary optics at the LED level (whichis a multi-LED package) to convert the lightdistribution into a controlled beam. Theplastic optics consists of a microlens arrayfabricated from polymethylmethacrylate(PMMA). This serves to minimize chromaticaberration due to first-order interference,while enhancing scattering to allow auniform visual appearance of light. Transmittancethrough the PMMA film is 92%.This patterned film is available in roll-torollsheets and therefore is flexible to applyin different shapes and sizes. Beyond thisprimary optic, a secondary optic, consistingof a hollow prism ring, modifies the light distributionand controls the light level transmittedto the target surface.Achieving omni-directionalityMarkus Hofmann, a senior developmentengineer with Osram GmbH of Munich,Germany, presented the pros and consof four different approaches to achievingomni-directionality with integral lampsfor residential applications. He said thatomni-directionality can be achieved usinglight guides, reflectors, a remote phosphoror a three-dimensional (3D) arrangementof LEDs.The key advantage of using light guidesOmni-directional lamp in base-up positionRepeat measurements invertical 45° and 90° planesfrom initial planeEnergy Star program requirements for integral LED lamps180°is that an incandescent-like bulb in appearancecan be achieved. However, there isgreat light loss and low efficiency associatedwith this approach, and meetingEnergy Star specifications (Fig. 2) is verydifficult. As a result, light-guide approachesare currently limited to low-lumen-output,design-driven applications.Meeting Energy Star requirements ismuch more practical if reflectors are usedinside the bulb to direct the light. Anotheradvantage is that a classical bulb designis possible. Hofmann said that reflectorsinside retrofit lamps currently work bestfor lamps with medium lumen output.When it comes to achieving high lumenoutput, the remote phosphor approach issuitable because light losses are low andthe phosphor is compatible with externalaluminum fins that function as the heatsink. The downside, particularly in today’smarket according to Hofmann, is the highcost of remote phosphors that contain rareearthmaterials. Assembly of the bulbs isalso a more complex process, he said, butEnergy Star requirements can be met.0°At least 5% of total flux (lm)in 130°-180° zone135°Luminous intensity (cd) at any anglein the 0°-135° zone shall not differfrom the mean intensity for the entire0°-135° zone by more than 20%.Source: OsramFIG. 2. Omnidirectionality is one of the more diffi cult requirements of Energy Star.Alternatively, a 3D arrangement of theLEDs can meet high-lumen-output needsand also meet Energy Star requirements.Hofmann stated that 60W-equivalent (850lm) and 75W-equivalent (1060 lm) lampsthat meet Energy Star requirements withgood CRI, CCT and lifetime have been fabricatedusing 3D approaches. “Realizationof 100W-equivalent lamps with 3DLED arrangements will be coming soon,”he added.Another presentation in the same sessionrevealed a less-traditional approach tofabricating and marketing retrofit lamps.Martijn Dekker, CTO of Lemnis Lighting,an LED lamp maker based in the Netherlands,announced that Lemnis has enteredinto a multiyear commitment with a largeretailer to develop and market cost-effectiveLED lamps. The first products are 400-lm and 200-lm lamps, which will be introducedin European stores soon. Althoughnot confirmed by Dekker, the retailer isthought to be Sweden-based Ikea. WhileDekker noted that the lamps do not meetEnergy Star requirements and have ashorter lifetime rating (20,000 hours) thanmost replacement lamps, the overridinggoal in development was achieving acceptableconsumer price points while deliveringquality lamps.“The price target for these lamps was lessthan €9.99 ($13.77) for the 45W-replacementlamp and €6.99 ($9.64) for the 25W-replace-30 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 ®