Thursday, 24 April 2014

A Guide to the Specification of LED Lighting Products - Part 1 of 4

Why Chose LED Lighting?

  • LED lighting is transforming the lighting industry, driving manufacturers in exciting new directions.
  • LED lighting has quickly superseded conventional lighting.
  • LEDs offer long lifetimes, energy and maintenance savings, making them an efficient energy saving solution. 

What’s so great about LEDs?

  • Unlike traditional lighting, LEDs provide millions of colours and dynamic effects meaning they are unrivalled in terms of design, scene-setting and ambience.
  • Thanks to their miniaturized dimensions and low heat radiation, LEDs can be embedded almost anywhere!
  • Due to their digital nature, LEDs can be programmed, offering an unlimited scope for creative use and effective energy management. 

Choosing the right LED

  • This document aims to educate consumers about the Lighting Liaison Group’s universal quality criteria for LEDs.
  • Using this criteria when selecting LED luminaires will allow you, the consumer, to judge manufacturers claims on an equal, like for like basis.
  • Applying the suggested criteria to all your LED purchases will ensure your luminaire is right for you. It will also eliminate any disappointment upon installation.

Key Terms
  • LED Die – The LED die or chip is a the fundamental light source
  • LED Package – The LED died is contained in a suitable package allowing simplified electrical connection or assembly
  • LED Module- This is the LED together with mechanical and optical component making a replaceable item for use in a luminaire
  • LED Luminaire- This is the complete system 
What is LED lifetime?
  • It is important to remember that lifetime claims based on lumen maintenance and luminaire life are two very different things. 
  • Lifetime claims based on lumen maintenance refer to the lumen maintenance projections of the LED light sources integrated into that luminaire.
  • Lifetime claims based on luminaire life are related to physical failures.
How is LED lifetime tested?
  • Many LED manufacturers use the LM-80 method to measure lamp life. This requires testing of LED light sources for 6,000 hours but recommends testing for 10,000.
  • It calls for testing three surface temperatures; 55°c, 85°c, and a third determined by the manufacturer. This means that users can see the effects of temperature on light output. The method also specifies additional test conditions to ensure consistent and comparable results.
  • In practice, LED manufacturers test their products for 6,000-10,000 hours and then apply extrapolation methodologies to produce LED luminaire specific curves.

Example LM-80 Calculation 

Constraints on LED lifetime test results...
  • There are differences in the results obtained from the LED die and those from the LED luminaire. This could be due to a number of issues including thermal management which can change the actual performance.
  • Catastrophic failure modes of individual LEDs and other failure modes of light output depreciation are not taken into consideration.
  • There is no valid way to translate the lumen maintenance curve of an individual LED light source into a curve for the LED luminaire.

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