Republication of Postings from the U.S. Department of Energy (DOE) Solid-State Lighting Program
by Jim Brodrick, U.S. Department of Energy
[At] LIGHTFAIR International, we saw a lot of T-LEDs (LED T8 replacement lamps), and it’s clear that manufacturers are putting a great deal of thought into how to make those products better, brighter, and easier to install. Because linear fluorescent lamps — which T-LEDs are intended to replace, and which are typically installed in recessed troffer luminaires — are the mainstay of indoor commercial lighting, DOE has put a lot of effort into providing helpful guidance to those who might be considering switching to T-LEDs or LED troffer replacements. A series of CALiPER reports (with accompanying video) explores various aspects of the topic, and our LIGHTFAIR training sessions on this important subject played to SRO crowds (the presentations are available online). We’ve also come out with a helpful fact sheet, Upgrading Troffer Luminaires to LED, which offers guidance on the various factors to consider when deciding on an LED upgrade to a fluorescent system.
There are three main LED options for such an upgrade: replacing the fluorescent lamps with LED lamps, replacing the fluorescent lamps and other luminaire components with an LED retrofit kit, and replacing the fluorescent luminaires with luminaires that were designed specifically for LED light sources. Selecting the best option for an installation depends on many factors, including the current lamp and ballast types and the condition of the fluorescent troffer luminaires, the desired photometric properties of the upgraded lighting system, the accessibility of the ceiling plenum, and the initial and ongoing economic goals for the upgrade.
Based on efficacy data from CALiPER, LED Lighting Facts®, and other programs, new LED troffer luminaires generally provide the greatest energy savings for equal luminaire output, followed by LED retrofit kits. In terms of initial purchase, LED replacement lamps often provide the lowest-cost option, with LED luminaires usually costing the most. Although replacement lamps that simply snap into the existing fluorescent sockets entail the lowest installation costs, most LED products marketed as replacements for fluorescent lamps require further modifications to the luminaire, thus driving installation costs up to where they’re comparable to those of many retrofit kits. And some retrofit kits may require so much luminaire modification that the installation costs end up approaching or even exceeding those for installing new LED luminaires.
Selecting an appropriate LED option depends on an assessment of current light levels and the extent to which they can be reduced. In cases where the existing light levels must be maintained, a full evaluation of the impact of the LED options on the light levels is needed. In cases where light levels can be reduced, the greatest savings may result from reconfiguring the layout to use fewer luminaires.
The light distribution also needs to be evaluated, since many LED options have different distribution characteristics than typical fluorescent troffers. In addition to increasing the chances of glare, this may also result in uneven light levels in task areas and reduced light on the walls. Detailed calculations or measurements of a mockup installation are needed to assess the light levels beneath and between luminaires.
LED options are available for lighting systems requiring dimming capability, although at present dimmable products in the replacement lamp category are less common, since it’s not common for the original fluorescent systems to be dimmable. However, if dimmable T-LEDs are being considered, it’s important to evaluate samples throughout the dimming range, paired with the exact type of dimmer to be used, in order to assess the possibility of flicker and color shift.
The color quality of the LED upgrade is another important consideration. All of the LED categories include products with a selection of CCTs, and all include products with CRIs in the 80s and higher, similar to fluorescent lamps. Still, LED products with poor color quality are available, often at low cost, so CCT and CRI ratings should be evaluated and product samples should be visually compared to the existing fluorescent products, to assess any noticeable differences in color quality.
There are a number of existing conditions to consider when upgrading troffer lighting to LED — such as the state of the sockets and the ease of access to the ceiling plenum. The new fact sheet also covers these, as well as safety certification and performance criteria. The millions of troffers in our offices, classrooms, and other commercial spaces offer considerable scope for achieving energy savings with solid-state lighting. But SSL is not a slam-dunk in such situations, and the right choices have to be made. The DOE resources that can help you make those choices are accessible online [here.]
