Project Lighting - April 2008 - (Page 17)

FeAtURe sponsoR ADveRtIsement ExpErimEntaL vErification Lumex’s 1-Watt High Brightness LuxLEDs™ Lumex’s latest addition to their family of high power products delivers maximum light from the smallest possible footprint. At only 1.8mm in height, Lumex’s new 1-Watt LuxLED™ emits a brilliant light with 30 lm @ If=350mA. In addition, the LuxLED™ can also provide at least 50,000+ hours of useable life. This powerful, new 1-Watt LED comes in a variety of colors including red, yellow, green, blue, as well as several shades of white. Lumex’s LuxLED™ is well suited for a variety of high brightness lighting applications and industries, including automotive, architectural, emergency lighting, traffic lighting and signage. Click here for more information LUMEX INC. 290 E. HELEN RD. Palatine, Il 60074 USA Phone: 800-278-5666 Fax: 847-359-8904 http://www.lumex.com/ index.aspx For this application, the junction temperature was measured using the forward-voltage characteristic. All four LEDs were calibrated with a 10-mA current source and, during the operational test, the current measurement source was on all the time. After stabilization, the operational current was switched off. The resulting drop in forward voltage was measured with a digital storage oscilloscope. The thermal mass of the junction is small, which resulted in a fast cool-down time. This temperature change occurred in less then 1 ms, so the forward voltage had to be measured in microseconds after the event. comparing rEsuLts the analytical/computational methods, and the error factor is within 16%. (Detailed measurement results are available on line.) The interface resistances and thermal spreading showed higher values in the experiment. Interface resistances are theoretically difficult to predict. Only an actual experiment can give the final answer and take account of manufacturing deviations. Considering the LED’s junction temperature limit of less than 120°C, and the calculated/measured junction temperatures shown in the table at left, the results show ample design margin. Therefore, the selected cooling solution (heat sink) is suitable for this application and there is no need to consider a highercapacity system. Contents Viewpoint Selecting HBLED Drivers for Lighting Apps Simulation Technique for Optimizing White-LED Design An Analytical Approach to Cooling HBLEDs Lighting News Home Page Product Training Module Online Ordering Suppliers Catalog Results foR diffeRent methods temperatures Corrected [°C] Parameter Ambient Heat Sink Base Metal Core PCB Below LED Junction Analytical 25 63 65 66 87 numerical 25 63 64 65 87 experimental 25 65 not meas 70 96 The accompanying table shows the results of all three analysis methods. The measurements offer a good comparison of 17 | Project lighting | aPr 08 http://digikey.com/ http://www.lumex.com/index.aspx http://www.lumex.com/index.aspx http://ad.doubleclick.net/clk;198717884;26055153;t http://ad.doubleclick.net/clk;195096871;25485867;e http://ad.doubleclick.net/clk;198717989;26055167;e http://ad.doubleclick.net/clk;198717988;26055168;e http://ad.doubleclick.net/clk;198717986;26055170;v http://ad.doubleclick.net/clk;198717985;26055171;v

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Project Lighting - April 2008 Contents Viewpoint About Project Lighting Sponsor Simulation Technique for Optimizing White-LED Design An Analytical Approach to Cooling HBLEDs LED Lighting Needs Smarts to be Competitive Lighting News Enter to Win an iPhone Refernce Materials Lighting Quick Links

Project Lighting - April 2008

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