When developing automotive rearlamps employing multiple LEDs manufacturers face inhomogeneity problems. Realizing brake and taillight function with the same LEDs introduces the need of dimming these LEDs. Widely used dimming methods are Pulse Width Modulation (PWM) and Constant Current Reduction (CCR). CCR has several advantages over PWM, including flicker-free operation and energy efficiency. On the downside, CCR can cause inhomogenity in rearlamps, at least in combination with traditional single binned LEDs. Recently introduced double-binned LEDs are selected (binned) at two different forward currents, according to brake and taillight level. Thus, the perceived inhomogeneity is reduced noticeably. In the worst case the LED with the minimum dorn, wavelength is placed next to the LED with the maximum dorn, wavelength. In this case the color difference is clearly noticeable by an observer regardless of temperature or forward current used At least double binning can reduce the minimum-maximum difference by factor 1.5 to 2, especially at the low current level. In contrast to single binned LEDs, double binned ones are sorted (binned) at high and low forward current level rather than high level only. With this knowledge we expect to measure the same behavior at high current level for both single and double binned LEDs. At low current level we expect a smaller variance for double binned LEDs. But in all measurement results, luminous flux as well as dominant wavelength, we see a smaller variance for double binned even at the high current level. The explanation is quite simple: When binning LEDs a second time (low level binning for the double binned LEDs) one reduces the variance at the first level too. Hence, double binning reduces the variance at high current level intrinsically. In the market of automotive rearlamps we often see designs where the observer can see one LEDs right next to its neighbor LED. In the case these designs are driven by constant current reduction (CCR) dimming method instead of PWM in order to avoid flickering effects (beads effect), double binned LEDs can reduce variances among the mounted LEDs. Visible inhomogenity can be reduced, but it is still challenging to eliminate them completely. Nevertheless double binned LEDs are an important improvement on the way to energy efficient, flicker-free automotive lighting without electromagnetic disturbance. The latter is an issue if one simply increases the PWM frequency without using shielded cable. CCR with double binned LEDs seems to be a good alternative.


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    Titel :

    Double-binned LEDs reduce inhomogeneity in rearlamps?


    Weitere Titelangaben:

    Reduzieren doppelt eingelagerte LED die Inhomogenität bei Rückleuchten


    Beteiligte:


    Erscheinungsdatum :

    2011


    Format / Umfang :

    10 Seiten, 7 Bilder, 3 Tabellen, 4 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch





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