driver life while also providing the required output power. This challenge is the hardest for drivers that are integral to screw-based lamps, because they cannot be moved far from the heat source.

For these reasons, the rated wattage of available LED lamps is still fairly small. The luminous efficacy of the LED devices has increased to a point where a lamp with a light output equal to a 60 W incandescent lamp consumes only 10 W. However, because of the thermal challenges, a 100 W equivalent lamp has not yet become available. As a result, screw-in LED lamps that are used as incandescent replacements in existing installations are at present limited to the lumen output of a 60 W incandescent lamp, although a 75 W equivalent has recently been made available.

Non-Integral Drivers

Commercial-grade LED luminaires are not constrained to use any particular form factors for the components. This is because luminaire replacement in commercial buildings is easier in dropped ceiling-type construction where there is ample room for luminaire housing and components, and replacement is, therefore, more readily performed. The drivers in these luminaires are typically separate from the LED module, and the luminaire may be designed so as not to present a thermal problem for the drivers. There is a trend in the industry to design “universal” drivers that produce either constant voltage or constant current output to the LED with input voltage ranging from 100 Vac to 277 Vac, which covers almost all global requirements. Having said that, today manufacturers of these drivers—quite often the same companies that also produce ballasts for fluorescent lamps—produce a wide array of products with differing specifications, while they are jockeying for market position. Standardization in the industry has started in some areas (see, for example, NEMA (2010a) and emerging standards by the Zhaga Consortium (2012)), especially for the interconnections between different components within the SSL luminaire (e.g., for standardizing electrical, mechanical, and thermal connections of the LED luminaire, including the LED module, the heatsink, the driver, and any lighting controls).

Most currently available drivers for interior lighting applications have relatively low output power, up to around 40 W. Some higher-output drivers, typically rated around 100 W, do exist for outdoor and industrial high-bay applications. It is likely that higher-output drivers will be needed in both interior and exterior applications in the future, when higher-light-output LED modules become available. The construction complexity of these products is similar to electronic ballasts for fluorescent lighting, and their assembly can be performed anywhere in the world. The potential number of different output configurations of LED drivers is much larger than for fluorescent lamps, mainly because fluorescent lamps are quite standardized, while LED designs are not. This may lead to fragmentation in the market in the short term, with manufacturers of the different component parts of an LED luminaire forming loose alliances to make certain that the products work together. It is also reasonable to expect a high level of obsolescence of driver designs, with older designs being replaced by those having different features during the time that the industry remains without standards. Indeed, the early designs from different manufacturers have been quite unique and not compatible with one another, so direct replacement of components within the LED luminaire, and sometimes even the replacement of the entire luminaire, can be challenging. Leading companies have recognized the need to rapidly develop standards, at least for the interconnections between the various components within the LED luminaire. As a result, the Zhaga Consortium was formed to develop these standards.

FINDING: Because of the large number of different ways to construct an LED lamp, industry has recognized the need for some levels of standardization and has organized to develop such standards.

The long expected life of an LED light engine will put pressure on the driver designer to produce designs that have equally long life ratings. Just as with integral drivers in incandescent replacement lamps, the weakest link in a nonintegral LED driver is the electrolytic capacitor that is used for energy storage in the ac-to-dc converter that is part of the driver. Research into other types of energy storage devices, perhaps ceramic capacitors with high capacitance and small size, may become necessary, and funding for it should be considered. Another way to solve this problem may be to create a new building infrastructure, where the ac-to-dc conversion is performed centrally, nearer to the utility entrance to the building. This enables the building to use only a few larger power ac-to-dc converters that may not be as cost constrained as in the case when the conversion is performed in every luminaire. At least one industry group, the EMerge Alliance,4 has been formed to investigate the possibility of a new electrical infrastructure and start the development of standards in this area. This application is currently limited to commercial buildings that use a dropped ceiling consisting of a ceiling grid and ceiling tiles, because it is envisioned that the elements of the ceiling grid are going to become the electrical conductors.

Drivers for OLEDs

The driver industry for OLEDs is at its infancy. It can reasonably be expected that the driver would look similar to, if not be the same as, a driver for LEDs, because the electrical requirement of both light engines are very similar. However, only a few experimental OLED luminaires have been produced so far, and experience driving them is limited. Both

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4 Further information is available at http://www.emergealliance.org.



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