The U.S. Department of Energy's CALiPER program has released Report 21.1, which is part of a series of investigations on linear LED lamps. Report 21.1 focuses on the performance of 31 types of linear LED lamps operated in a typical 2x4 troffer with a K12 prismatic lens. The lamps were intended as alternatives to T8 fluorescents.
While the lensed troffer reduced the variation in luminous intensity distribution noted in Report 21, it did not eliminate it; there was still some difference in performance that could be undesirable in a lighting installation. For instance, the lamps with a narrower distribution (i.e., with a clear lens) resulted in a slightly smaller spacing criterion for the luminaire, which may result in uneven workplane illuminance. Lamps with a narrower distribution resulted in a higher luminaire efficiency than those with a wide distribution (i.e., with a diffuse optic), and all of the linear LED lamps resulted in a higher luminaire efficiency than the fluorescent benchmark.
The marginal gains in efficiency for narrow-beam lamps cannot overcome broader differences in lamp efficacy, however. Thus, in choosing a lamp for energy savings, lamp efficacy should be the primary consideration. Luminous intensity distribution may be a secondary consideration, with clear lamps providing slightly higher luminaire efficiency but also potentially resulting in lower workplane illuminance uniformity.
Overall, many of the tested linear LED lamps provided higher luminaire efficacy than a comparable fluorescent system in a K12-lensed troffer. On average, the LED-lamped, K12-lensed troffers were approximately 25 percent more efficacious than the fluorescent benchmark. About one-third of the LED products provided lumen output approximately equivalent to a fluorescent system with the same number of lamps.
Given the disparity in cost between LED and fluorescent systems, the financial benefit and long-term cost savings associated with LED retrofits should be considered on a case-by-case basis.
