Lighting : February 2014 Lighting (v2-HR)
50 LIGHTING MAGAZINE | February/March 2014 February/March 2014 | LIGHTING MAGAZINE 51 FORM AND FIT The LED lamps were first measured to determine whether they would fit within the physical MR16 envelope. It is important to comply with these dimensions, to ensure compatibility with existing luminaires. Unfortunately, two types exceeded the length requirement, which could lead to lamps that protrude below the ceiling when installed into an existing luminaire. It was noticed in this preliminary investigation that two lamp brands were physically identical in every way. This could be seen as unusual, as LED chips lend themselves to all manner of arrays and heat sinks. The two lamps in question had identical housings and strikingly similar packaging, including the safety advice on the box. Yet the two brands were from companies that are not normally associated with each other. Testing revealed that the spectra for the lamps were different, indicating that different chips were sitting in the same body type. This raises several points. The first concerns heat sinks. It has been well established (e.g. Lighting April/May 2012 issue) that good heat sink design is vital to the performance and longevity of LED product. It could be questioned whether a generic heat sink will lead to an inferior product, which has not been designed with specific chip performance in mind. Secondly, consumers are accustomed to replacing “like for like” and often take the failed lamp (or its box) to a store in order to purchase a replacement. Given that these two LED lamp types have the same description and physical appearance, the consumer could be led to believe that they are the same product. Yet photometric data shows that they are not. LUMEN OUTPUT Only three of the lamps listed their lumen output on the box. These lamps were tested in Massey University’s integrating sphere, using methods based on LM-79-08i. It was found that some of the samples exceeded the stated lumen outputs, though average figures were just below FEATURE BY SUSAN MANDER Misinformationappearsrifeandrecent anecdotes have caused concern. In one shop, a customer was urged to buy an LED retrofit lamp as it had higher efficacy. The fact that the replacement lamp provided only a quarter the lumens of its supposed halogen equivalent appeared to be irrelevant to the shop assistant. In another store, a ‘sparky’ was heard to insist that the product that he’d imported directly from overseas was just as good as a well established brand, as his lamps were “still working so far”. This type of self-testing appears to be common when evaluating lamp performance but again fails to recognise the key performance criterion of lumen output, let alone colour properties, or either of these qualities over time. So, what are residential consumers actually getting? A recent study at Massey University set out to put LED retrofit lamps to the test. Low voltage MR16 lamps were specifically chosen, due to their popularity in New Zealand homes. To the uninitiated, “MR” stands for “Multi-facetted Reflector”, which in this case has a diameter of 16 eighths of an inch (a roundabout way of saying two inches). A typical halogen example is shown in Figure 1. The experiment used eight lamp types, which were all readily available in New Zealand at the time of the study. Six samples of each brand were used to evaluate consistency across the type, giving a total of 48 LED lamps. These days, impressive boasts of high efficacy and long life have made LEDs the byword for energy efficient lighting. Yet, hiding amongst the high-quality praiseworthy products there lurk inferior imposters that tag along with LEDs’ good name. So how can you tell the good from the bad? How do LED MR16 retrofit lamps measure up? FIGURE 1. The incumbent technology; a halogen MR16 lamp.
April May 2013
Lighting April 2014 - Vol 34 Issue 2