LEDs Measurement Considerations
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LEDs Measurement Considerations - 1

LEDs Measurement Temperature change of a white HPLED with time Email: contact@majantys.com Website: www.majantys.com time (hh:mm:ss)

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LEDs Measurement Considerations - 2

LEDs Measurement Considerations Introduction The High Power LEDs - HPLEDs - are a very interesting alternative to the conventional lamps, such as fluorescent, incandescent or discharge. Particular advantages are very small dimensions, reduced power consumption, very long lifetimes and selectable precise colour etc. In order to obtain maximum benefit from this technology it is essential that all the components such as the semiconductor chip, an efficient heat sink, well designed lenses and a current stabilised driver circuit are suitably integrated. The environment of the LED directly...

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LEDs Measurement Considerations - 3

LEDs Measurement Considerations Measuring a HPLED without any warm-up The intensity and the colour of a HPLED are stable once the component has reached a steady state, i.e. the normal operating temperature has reached and does not change over time. This steady state behaviour is typical of any electronic component with a high resistance following switching on and warming up. This is affected both by the device itself Photometry (calib.) : Figure 3 : Screenshots of the PhotonProbe software associated with the To demonstrate this effect a white, high power LED was switched on and its optical...

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LEDs Measurement Considerations - 4

LEDs Measurement Considerations in real time by attaching a type K MCPCB and the chip itself. intensity results - figures 4 to 6, we show a variation of the colour More specifically we observed variations change was switched off. Over this period there is a significant of the module starting from hour, there is still a variation, both in intensity and colour slower rate of change. Temperature change of a white HPLED with time time (hh:mm:ss) Figure 4 : Temperature of the HPLED increases with time, Intensity change of a white HPLED with time Figure 5 : Photometric intensity decreases with...

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LEDs Measurement Considerations - 5

LEDs Measurement Considerations colour change have all temperature controlled there measurements were started summarized in table 1 below. They are calculated from the change in the measured spectra Colour change of a white HPLED vs. warm-up Figure 6 : Colour change of the HPLED with time, from t = 0 to Figure 7 : Spectrum acquisitions from t = 0 to 2:30 hours using the Probe4Light. All colour parameters are calculated from these spectra. iKnowledge by color science 17 Allee du Lac d'Aiguebelette, 10 Bat. Arche Email: contact@majantys.com —Website: www.majantys.com

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LEDs Measurement Considerations - 6

LEDs Measurement Considerations Experiment-timeH AT—Temperature- Al—Intensity Ax—Colour- Ay—Colour- change-(°C)H change-(%)H change-xH change-yH Table 1 : summary of the observed variations for the main colour variables as function of elapsed time. Other colour parameters, very popular in the LED industry, also vary with time as shown in table 2. The Correlated Colour Temperature - CCT - loses 130 K and the Colour Rendering Index (CRI) varies between 0.4 and 0.7 depending on the selected method (8 or 14 references). According to the specifications of the LED manufacturer, a variation in the...

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LEDs Measurement Considerations - 7

LEDs Measurement Considerations Experiment and results Conclusion The Probe4Light is a reliable spectrophotometer to evaluate precisely the optical performances of LEDs in their industrial environment. The temperature measured is not the junction temperature which is normally specified by the manufacturers of LEDs. However the measured temperature correlates perfectly with the changes in colour and intensity. In such measurements it is important to know the warm up time of the module, in order to ensure measurements are taken when the LEDs output no longer varies. Depending on the level of...

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