Over the past two years, light-emitting diode (LED) luminaires have begun competing effectively against the fluorescent troffer as performance increases and costs decrease. With nearly 1 billion fluorescent luminaires installed in the United States, according to the Department of Energy (DOE), this is a big opportunity.


However, it’s possible to keep the hardware but replace the lamps with linear LED models. In recent years, these products have come a long way in performance and cost. The primary value proposition is energy savings and longer service life. The DOE tested this and published the results in three CALiPER program reports in spring 2014.


The first report evaluated bare-lamp photometric performance. In accordance with the IES-LM-79 standard, testing covered light output, input watts, efficacy, color, power factor and beam angle for 31 products purchased in late 2012. The fact that the products were purchased 21 months ago is important to remember, as the technology is continually improving.


The majority of products have a T8 designation and replace fluorescent T8 and T12 lamps. In a linear LED lamp, the light-emitting section faces the workplane. The lens may be clear or frosted; clear lenses tend to produce more light output and a narrower beam angle. Most linear LED lamps use the same bi-pin connections as a fluorescent lamp and can be installed similarly. They bypass the existing ballast and instead use an internal or external driver powered directly from the main voltage. Different manufacturers use different approaches to driver location, socket and wiring.


The DOE found the average light output of the tested LED lamps was half as much as the benchmark fluorescent 32-watt (W) T8. Wattages ranged from 16–29W with an average efficacy of 94 lumens per watt (LPW), in the neighborhood of a fluorescent T8. To show how the technology is continuing to improve, the mean efficacy of LED linear replacement lamps in the Lighting Facts database—based on about 1,000 products—was 103 LPW in the first quarter of 2014. 


While many of the products were rated as “cool white” (4,000K) with a color rendering index (CRI) rating of 80+ (considered “good” for many general lighting applications), some were limited to a higher color temperature (cooler appearance) and a lower CRI of 70+. Furthermore, measured light output or input watts differed by more than 10 percent from what the manufacturer claimed in nearly half of the products.


The LED lamps were found to produce similar efficacy as fluorescent lamps but typically with lower output. Therefore, satisfying desired light levels usually depends on the directionality of the LEDs to increase luminaire efficiency (more light exiting the luminaire).


The second DOE report evaluated test LED lamps in a typical 2-by-4 troffer with a K12 prismatic lens. The results confirmed that the directionality of the LED lamps increased luminaire efficiency—from 75 percent for the fluorescent benchmark to an average 82 percent. LED lamps with a clear lens produced higher luminaire efficiency than those with a diffuse lens. The average installed LED lamp operated at a 25 percent higher efficacy than the T8 system. However, only about one-third of the LED lamps produced light output comparable to the fluorescent luminaire.


While the directionality of the LED source increases luminaire efficiency, it poses certain risks, such as changes to light-level uniformity on the workplane, aesthetics and glare. The DOE found that lamps with a narrower distribution (i.e., clear lens) resulted in a slightly smaller luminaire spacing criterion, which could reduce uniformity of light levels across the workplane. The DOE also concluded that clear-lens lamps with a beam angle of less than 120 degrees could make the luminaire appear “stripey,” which may affect perception of glare and lighting quality.


In the last report, the DOE went one step further by installing three LED lamps and the fluorescent benchmark lamp in five different troffer types. The DOE concluded that, based on the photometric testing and the observer responses, LED lamps may work well in some troffers but poorly in others. While LED lamps can improve luminaire efficiency in K12-lensed and parabolic troffers, they produce little change in volumetric and high-performance-type troffers and can reduce efficiency in recessed, indirect troffers. These changes can be accompanied by tradeoffs to visual appearance and comfort, particularly when LED lamps with clear lenses and narrow light distributions are installed.


LED linear lamps can be a cost-effective retrofit, particularly when utility rates are higher, hours of operation are long, and their installation time is shorter. However, they present some risks. Products are available in a variety of configurations, with various ramifications for safety and maintenance. Some take longer to install. There is a wide variation in performance, requiring careful evaluation. Manufacturer claims varied from DOE-tested performance for some products, so it may be wise to test products in their intended application prior to commitment. Additionally, installation may result in lower light levels, which may be suitable for overlighted applications but not others. Finally, clear-lens lamps with narrower distributions may result in higher output and efficacy but impose tradeoffs to uniformity and aesthetics in some applications.