Justin Maeers outlines some of the issues surrounding the misrepresentation of the efficacy of luminaires using light-emitting diodes.
The integration of LEDs (light-emitting diodes) into luminaires to produce solutions that meet the needs of the market, replacing more traditional inefficient short-life lighting, is dominating much of the industry’s product development.
The market has become increasingly aware of the benefits of installing LED lighting fixtures, which has led to some manufacturers taking advantage of the buoyant market and making LED light fittings that will not perform as claimed in their data sheets. To make product more marketable, many manufacturers of LED luminaires are keen to misrepresent their product data, in many cases boosting the true data by over 400%. False claims are made about the energy efficiency, light output and life expectancy of products.
Performance data produced by the manufacturer is vital for predicting and understanding how LEDs will perform in actual use, as opposed to ideal test conditions. It is essential that the providers of LED chips to the lighting industry standardise the way performance data is provided to enable accurate information to be provided by luminaire manufacturers. When comparing data sheets from different manufacturers, it is very easy to become confused, as there are currently no standard formats for measuring and quoting the expected life of an LED.
Many manufacturers of LED luminaires quote the lumen output of their luminaires directly from the chip manufacturer’s datasheet — without taking into account thermal, optical and electrical inefficiency. LED manufacturers generally quote the efficiency of their LEDs at a junction temperature of 25°C. In a luminaire, the junction temperature will be significantly higher. As the temperature increases, efficiency falls off and less light will be given out (for a 50 K temperature rise, the light drop off may range from 3 % to 15% depending on the design of the LED chip). Unfortunately this can lead to poor performance and misinformation.
The more current used to drive an LED, the less efficiently it performs. This drop off in performance varies from manufacturer to manufacturer, but can be up to 40% when the drive current increases from 350 to 700 mA.
Optical efficiency ranges from 50 to 95%, depending on the quality of material and design of the lens or optic. Most luminaires have secondary optics fitted to control the light spread of the light fitting. This is often not taken into account in data from LED manufacturer as they do not know what optical system the luminaire manufacturer might use.
Driver efficiency can vary from 50 to 90%, depending on the design and quality of the driver being used and the quality of its internal components.
When quoting efficacy, the calculation is total luminaire lumens divided by total circuit wattage. There will be losses in the LED driver that cannot be taken into account by the LED manufacturer, which will not know what driver will be used). The luminaire manufacturer should therefore measure the total circuit wattage and actual total lumen output at stable running temperature and use these figures to calculate luminaire efficacy.
The table demonstrates the different results that may be achieved and claimed by a lighting manufacturer. It can be clearly seen that it is easy to misrepresent the output and efficacy of a luminaire. It is equally easy to misrepresent the life of a luminaire.
An LED chip manufacturer may rightly claim a life of 100 000 hours plus if operated, for example, at 25ºC and at 350 mA. In practice, however, these figures do not apply when LEDs are incorporated into a luminaire. In a poor luminaire design, the LED temperature could be higher than 150ºC, making its life extremely short.
With such disparity surrounding life claims and chip manufacturers testing processes in different conditions, what chance does the market have of receiving reliable information? Until industry standards are set, the problem of misrepresentation will continue. It is therefore important to check carefully before purchasing any LED luminaires that absolute photometry has been used when establishing a luminaire’s light output and that the entire system power consumption (including driver) has been used when calculation efficacy.
Justin Maeers is managing director of Collingwood Lighting www.collingwoodlighting.co.uk