11.50 Thursday 15 June

Extreme temperatures - 4 things you need to know about outdoor lighting 

by Lawrence Baynham MEng MA (Cantab)

An overview of what can go wrong if luminaires are exposed to extreme temperatures, and features to look out for to mitigate the risks. 

LED fixtures are being used across the globe to enable energy savings from traditional HID (or older) technology. Depending on the installation site, the ambient environment could be as low as -65 degrees (recorded in Russia) to as high as +40 degrees (night time temperature recorded in Iran). In order to remain robust against this extremely wide operating range of over 100 degrees, luminaire manufacturers must introduce designs that mitigate the risk of failure at extreme temperatures. 

The paper will start with an overview of the global climates, and a discussion on uncertainty stemming from the impacts of global warming and climate change. 

Details of the 4 key failure modes associated with temperature will be discussed: thermal shock, ESR shift of electrolytic capacitors, lumen depreciation and accelerated wear out of electronic components; 

  • For thermal shock, the construction of the LED will be discussed, with details of bond-wire technology and how thermal shock can result in an open circuit situation within the LED component. Lawrence will explain how this effects a constant current LED system. 
  • We'll look at the impact of ESR shift and its implications for other circuit elements. 
  • Whilst commonly understood lumen depreciation will be reviewed in the context of extreme conditions (focusing on the widely-used TM-21 calculation) as well as a qualitative and quantitative perspective on the link between temperature and lumen depreciation. 
  • The accelerated degradation of wear-out electronic components (such as wet electrolytic capacitors) is highlighted, along with details of the correlation between temperature and lifetime, as explained by the Arrhenius equation. 

Finally, Lawrence presents a range of design solutions used to mitigate the risks presented by the above, with an overview of the latest technology available from luminaire manufacturers.


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