Integrating LEDs into luminaires has become a significant part of the lighting industry’s product development. But in the rush to take advantage of the buoyant market, some manufacturers are putting LED light fittings on the market that do not perform as well as their datasheets would suggest.
In a bid to make their products more marketable, many LED luminaire manufacturers misrepresent their product data, in some cases boosting the true figures by over 400 per cent.
Performance data produced by the LED manufacturer is vital if the luminaire designer is to know how the sources will perform in actual use, as opposed to under controlled test conditions.
Set a standard
It is essential that the providers of LED chips standardise the way this data is presented so LED luminaire manufacturers can provide accurate performance information. However, there are no set standards for measuring and quoting the expected life of an LED.
Many LED luminaire manufacturers quote directly from the LED chip maker’s datasheet, which generally assumes the LED will run at a constant temperature of 25°C. In a luminaire however, the temperature will be significantly higher, dramatically reducing LED efficiency and light output. For a 50oC rise, the reduction in light output may range from 3 to 15 per cent – depending on the design of the LED chip.
As the forward current is increased, the efficiency of the LED will be reduced even further – between 3 and 10 per cent less light with an increase from 350 to 700mA. Optical efficiency ranges from 50 to 95 per cent depending on the quality of the lens or optic material. Driver efficiency can be anything from 50 to 90 per cent depending on the design of the driver and its internal components.
Theory and reality
The table shows the different results that may be achieved and claimed by a lighting manufacturer using three LEDs rated at a minimum flux of 70 lumens at 25oC, 350mA and 1W.
So it is easy to misrepresent the life, output and efficacy of a luminaire. An LED chip manufacturer may rightly claim that the life of its LED is 100,000 hours if operated at 25oC and at 350mA.Yet this will never be the case when the LEDs are built into a luminaire. In a poor design, the LED temperature could be higher than 150oC, making its life extremely short.
Don’t get caught out
So how can specifiers be sure they are getting a product that does what it claims?
First of all, check the supplier has tested the complete luminaire, not just the light engine, and has tested it to absolute photometry. Most importantly, always buy from a reputable LED specialist.