According to the U.S. Department of Energy (DOE), more than 360 million troffers (named for a cross between trough and coffer) provide general lighting in commercial building interiors. With their standard dimensions of 2-by-4, 1-by-4 and 2-by-2, these luminaires are popular in dropped, acoustical-tile ceilings with a low ceiling height (less than or equal to 9 feet).

The installed troffer base is predominantly linear fluorescent. In recent years, the development of LED technology has resulted in a broad selection of products designed to challenge fluorescent, offering up to 70 percent energy savings, longer life and controllability. The opportunity remains largely untapped, however, with LED luminaire penetration currently estimated at just 1 percent of the installed linear lighting base.

Three major options are available: replace the lamps with tubular LED (TLED) replacement lamps, replace the lamps and other components with an LED retrofit kit, or replace the luminaire.

This article reviews the state of the art in TLED and LED troffer technology and identifies key factors that can inform a decision about whether to retrofit or replace.

TLED lamps and kits

TLED lamps are designed to replace linear fluorescent lamps. As such, they offer a nominally low-cost option to gain LED benefits while retaining the fluorescent luminaire. TLED retrofit kits package TLED lamps with necessary electrical and optical components to offer a repeatable solution.

Viable products are available with numerous choices, including 4-foot, 2-foot and U-bend sizes. In June 2016, DOE’s Lighting Facts database listed more than 4,500 commercially available TLED products. Sales data suggests significant traction. According to the National Electrical Manufacturers Association, TLED lamps accounted for 12.8 percent of member linear lamp shipments, compared to 63 percent for T8, 14.8 percent for T12 and 9.4 percent for T5 in the third quarter of 2016.

Many configurations are available. The majority feature a T8 designation (1-inch diameter) and same bi-pin bases to connect the lamp to the luminaire’s lampholders. The complete lamp contains the LEDs, optics to distribute the light output and heat sinking.

The lamp may operate directly on a fluorescent ballast (UL Type A), feature an internal driver (UL Type B) that bypasses the existing ballast or work with an external driver (UL Type C) that replaces the ballast. As a “drop-in” lamp, Type A offers the simplest installation, though with less efficacy due to ballast losses; retaining the existing ballast also requires interoperability and introduces an additional point of failure. While Type B is very common, it requires bypassing/removing the ballast and delivering alternating current (AC) mains voltage to the lamp sockets. Type C requires ballast removal and connecting the driver to the sockets using low-voltage wiring; it offers high efficacy, ability to operate multiple lamps on each driver, and, potentially, dimming and control capabilities.

In each of the above cases, the installer may also need to replace the lampholders. If electrical modification is performed during installation, the luminaire’s original safety certification and warranty may be considered invalid. The authority having jurisdiction may require field inspection to recertify the luminaire, which may impose additional cost. The alternative is to use a TLED retrofit kit certified and marked as “classified” by a nationally recognized testing laboratory.

In February, the American National Standards Institute revised two key industry lamp and lampholder standards to include a new G6.6 (Snap-Fit) design, a base with two internal pins and an additional ground pin that mates to an accompanying lampholder. This provides the TLED a dedicated connector system specifically designed to mechanically hold and power TLED lamps across a wide range of voltages.

A DOE Lighting Facts Snapshot Report published in June 2016 provides interesting data. Among the 4,500 TLED products in their database, about two-thirds were 4-foot, with a mean light output of nearly 2,100 lumens. About nine out of 10 TLED lamps had an efficacy exceeding 100 lumens per watt (LPW), about the same as a bare linear fluorescent lamp.

However, we must account for adjustment of light output and efficacy after a bare lamp is installed in a luminaire, which typically reduces output based on the luminaire’s optical design. Efficacy was found to decrease if the luminaire had more lamps. While the directionality of the LEDs improves luminaire efficiency, there are still losses. DOE applied a factor of 0.8 to account for these light losses, resulting in a net efficacy of 91 LPW. That is less than the average 102 LPW for dedicated LED troffers.

In 2016, the DesignLights Consortium (DLC) rolled out new technical requirements. DLC maintains the Qualified Products List, which many utilities use to qualify LED products as being eligible for rebate programs. A minimum bare-lamp efficacy of at least 110 LPW is required, or 100 LPW as tested in a typical luminaire.

The majority of TLEDs in the Lighting Facts database offered 3,000K, 4,000K or 5,000K correlated color temperatures (CCT)—essentially warm- or cool-white. As with LED troffers, there is a relationship between CCT and efficacy, with efficacy declining 3 LPW per 1,000K CCT decrease. Nearly all products in the database offered a color rendering index (CRI) rating in the 80s, which is considered good for typical indoor general lighting. Unfortunately, due to changes in lamp testing requirements and other market changes, DOE stopped listing LED replacement lamps in Lighting Facts in December 2016, though it continues to list TLED retrofit kits.

LED troffers

LED troffers provide a complete replacement solution as opposed to a component-based one. Installation is straightforward, resulting in new lighting that is purpose-built for the light source and typically compatible with dimming and controls.

DOE projects that more than half of all installed commercial linear luminaires (troffers, suspended, etc.) will be LED by 2025 given the technology’s current adoption.

According to the Better Buildings Alliance, high-efficiency LED troffers (at least 125 LPW) can deliver up to 70 percent energy cost savings compared to traditional fluorescent troffers. That number goes up to 80 percent if integrated with lighting controls.

As of December 2016, Lighting Facts listed more than 7,300 LED troffers/grid ceiling luminaires. Among those products that listed a specific luminaire size, the majority produced comparable light output as their fluorescent counterparts do, but with higher efficacy.

All listed LED troffers products presented a mean efficacy of 102 LPW, comparable to fluorescent troffers up to 100 LPW. More than 10 percent had an efficacy greater than 125 LPW. DLC requires a minimum efficacy of 100 LPW to be listed as DLC Standard in the Qualified Products List and 125 LPW to be listed as DLC Premium.

While Lighting Facts LED troffers generally had a lower efficacy than TLED bare lamps, they were comparable to the high end of TLED efficacy after factoring in light losses after the TLED lamp is installed in a luminaire.

Nine out of 10 listed LED troffers had a CRI in the 80s. They also had CCTs of 3,000K, 3,500K, 4,000K, 5,000K or 6,500K.

Retrofit or replace

Many factors must be considered as part of a lighting upgrade, which we can narrow in regards to comparing whether TLED or LED luminaires are a more suitable option for a given project. The most important aspects are light level, including uniformity; light distribution, including visual comfort; aesthetics; the condition of the existing’s lighting system; cost, including ease of installation; and compatibility with controls.

Light level: Lighting’s primary job is to produce light needed for productivity, safety and more—not save energy. The new lighting must produce sufficient maintained light levels on the workplane. In many general lighting applications, it must distribute the light uniformly across the workplane.

If existing light levels must be maintained, evaluate LED products to ensure they provide sufficient maintained light output. If the space is overlighted and light levels can be reduced, some LED lamps and luminaires offer reduced light output and wattage. Another opportunity is to redesign the lighting system with new and fewer LED luminaires.

Light distribution: This describes the luminaire’s light-emission pattern; where it places light and at what relative intensity. It is a critical consideration for LED lamps and luminaires, as LED lamps may change the fluorescent luminaire distribution, and LED luminaires offer a broader range of distribution choices.

If the light distribution is narrow relative to the luminaire spacing, light levels could become inconsistent across the space, with relatively dark spots between luminaire rows. If light distribution is broad, the output must be visually comfortable, with no direct glare at typical viewing angles. The advanced optics in some LED luminaires allows wide spacing, meaning it may be possible to install fewer luminaires in an upgrade project involving a redesign. Well-designed LED luminaires also minimize glare, may eliminate a perceived light source and place light on the walls, which can make the space appear brighter and more visually comfortable.

Aesthetics: The selected option should produce a desirable space appearance, a visually comfortable environment and a perception of lighting quality. The option’s color quality should be appropriate for the application or otherwise match the existing fluorescent lighting system.

Existing conditions: Fluorescent luminaires that are relatively new and in good condition lend themselves more to TLED retrofits, while older luminaires with significant wear and tear are more eligible for luminaire replacement. If working above the ceiling is prohibitive, a TLED retrofit will be more desirable. If a TLED retrofit kit will be installed, ensure the existing luminaire can physically accommodate it. Check to determine if the existing sockets require replacement; if not, ensure they are in suitable condition to deliver the required voltage to the lamps. If the TLED lamp will operate on the existing ballast, ensure the lamp and ballasts are compatible.

Cost: This involves the installed cost, including equipment and labor, as well as operating cost, including energy and maintenance. Equipment purchase costs generally increase from TLED lamps to TLED retrofit kits to new luminaires. Installation labor costs are typically lowest for UL Type A TLED lamps, while TLED lamps requiring electrical modifications will impose a higher cost, which may include safety certification costs. TLED retrofit kit installation typically imposes a higher labor cost than TLED lamps, and, if significant electrical modification is required, this cost can come to close to or top the labor cost of installing new luminaires.

Compatibility with controls: LED luminaires are typically available with dimmable drivers and compatible with various controls, which may be embedded in the luminaire. TLED lamps and kits offer limited dimming options, with few available products. Verify compatibility between LED products and controls to ensure reliable, flicker-free performance.

Retrofit or replace?

Every option should be vetted based on the above checklist and the application requirements. Resources such as the DLC’s Qualified Products List ( can provide access to product options verified as achieving a designated performance standard. DOE also publishes fact sheets that can provide guidance about evaluation.

A trial installation with personal evaluation is often recommended. While LEDs can provide good energy savings, ECs should ensure it always provides good lighting first.