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Due to the banning of incandescent lamps, general lighting is nowadays based on light sources utilizing light emitting diodes (LED). The lifetime of LED lamps is one of the key issues in estimating the costs of light installations. The expected lifetimes are long, tens of thousands of hours. Thus, ageing the lamps throughout their expected lifetimes to predict their behavior is extremely time consuming. Methods to predict lifetime behavior in significantly shorter time frames are needed.

We have a lighting experiment going on since 2009. In this experiment, five types of retrofit E27-based LED lamps are operated under ordinary room conditions and measured periodically for luminous flux, electrical current, and spectral properties [1]. The junction temperature of LEDs is one of the main factors that affects the lifetime of luminaires based on high power LEDs. This was studied by ageing lamps both at elevated temperatures and at ordinary room conditions, and comparing the results. It appeared that modest heating can be used to enhance the ageing, whereas too much heating may cause new failing mechanisms.

Junction temperature of LEDs can to some extent be measured externally from the produced spectral irradiance properties [2]. This junction temperature can be further used to predict ageing and early malfunctioning of LED luminaires [3]. LEDs operated at high temperatures tend to break earlier than LEDs operating at lower temperatures that should be taken into account in the design of luminaires.

LED technology saves energy, which can be even extended by using adaptive control of the luminaires. We have another ongoing experiment on ageing LED street light luminaires both under steady conditions, where lights are only turned off for day-time, and under conditions mimicking use of lights only when cars or pedestrians are present [4]. The results indicate a small but existing increase in costs of the installation due to increased ageing rate induced by thermal cycling of LED chips under active control.

Contact persons: Petri Kärhä and Ville Mantela

References

[1] H. Baumgartner, D. Renoux, P. Kärhä, T. Poikonen, T. Pulli, and E. Ikonen, “Natural and accelerated aging of LED lamps,” Lighting Res. Technol. 48, 930–942 (2016).

[2] A. Vaskuri, H. Baumgartner, P. Kärhä, G. Andor, and E. Ikonen, “Modeling the spectral shape of InGaAlP-based red light-emitting diodes,” J. Appl. Phys. 118, 203103, 7. p. (2015).

[3] A. Vaskuri, P. Kärhä, H. Baumgartner, O. Kantamaa, T. Pulli, T. Poikonen, and E. Ikonen, "Relationships between junction temperature, electroluminescence spectrum, and ageing of light-emitting diodes," Metrologia 55, S86–S95 (2018).

[4] J. Askola, P. Kärhä, H. Baumgartner, S. Porrasmaa, and E. Ikonen, “Effect of adaptive control on the LED street luminaire lifetime and on the lifecycle costs of a lighting installation,” Lighting Res. Technol. 54, 75–89 (2022).