How do plug-and-play T8s stack up against ballast-bypass LED lamps?
Nowadays, several manufacturers have introduced so-called plug-and-play LED linear lamps — fluorescent replacements that require no rewiring and simply snap into place. These solutions are more expensive but easier to install than LED linear tubes that require removal of the ballast and direct connection to line voltage — a task best performed by a qualified electrician. However, both approaches have their pros and cons. And both approaches are significantly less expensive than replacing the whole fixture.
We will review the performance and financial considerations associated with ballast-bypass and plug-and-play LED linear lamp installations for offices, schools, retail outlets, and hospitals. We will also discuss the electrical safety concerns that have been raised regarding LED linear lamps. Most importantly, the article will discuss the features to look for when considering LED linear lamp purchases.
Fluorescents versus LEDs: Then and now
Philips estimates the current installed base of fluorescent tubes at 12 billion sockets globally. In 2010, the US Department of Energy (DOE) estimated there were nearly 1 billion fluorescent luminaires installed in the United States, 60% of which were T8s (tubular, 8/8- or 1-in. diameter). Fluorescent T8 luminaires are mainstays in schools, hospitals, grocery stores, warehouses, and office spaces in the United States, but also in many other parts of the world.
In grocers and big-box stores, linear LED replacements have been making significant inroads in refrigerated display-case lighting. This is an ideal application for linear LED lamps because lifetime of the LEDs is extended in cold environments and the lamps don’t emit heat like fluorescent tubes, providing further savings on cooling costs. Because speed of installation is critical to grocery store owners, case lighting is a key target application for plug-and-play LED linear lamps.
Despite the success of LED linear lamps in this one application, they have struggled to compete with fluorescents across the board due to fluorescent tubes' relatively high efficacy (90 lm/W), long life (30,000 hr), and low cost. Priced at $3 per tube relative to $30 or more for an LED linear lamp, the LED replacement must match the fluorescent's light quality while significantly improving the energy efficiency to offer a reasonable return-on-investment (ROI) period. Nonetheless, as the performance of solid-state lighting (SSL) has steadily improved, LED linear lamps have become more competitive in terms of light quality and efficiency.
However, as was pointed out in a recent US DOE series of Caliper reports (Reports 21, 21.1, 21.2, and 21.3), not all LED linear lamps are created equal and lamps must be evaluated on a case-by-case basis. Report 21 began by testing the photometric performance of 31 linear LED lamps (sold in late 2012 and early 2013) and benchmarking them against 32W fluorescent tubes. Upon testing, only 8 LED lamps achieved the DesignLights Consortium (DLC) requirements for bare lamp efficacy (≥100 lm/W) and output (≥1600 lm), and only one lamp achieved output comparable to a 32W fluorescent (3126 lm) as shown in Fig. 2. Reports 21.1 and 21.2 evaluated 31 linear LED lamps in K12-lensed troffers and then three lamps in five different troffer types, respectively. When LED linear lamps are in a luminaire, multiple factors determine the luminaire output and luminous distribution including the lumen output and luminous distribution of the lamp, lamp cover (clear or diffuse), and troffer type.
In the prismatic K12 lensed troffer, 10 of the lamps provided lumen output comparable to the fluorescent and one lamp provided higher lumen output, with 20 lamps measuring lower output. Higher efficacy was maintained with K12 lensed and parabolic troffers, while recessed indirect troffers tend to reduce the efficiency of LED lamps to below that of fluorescents unless the LED lamp uses a high beam angle (Fig. 3). The Caliper study also indicated that observers preferred LED lamps with diffuse covers over clear lamps, and the diffuse lamps also lead to a luminous intensity distribution closer to that of a fluorescent tube's distribution, which is also preferred.
What does plug-and-play mean?
Still, the market potential has lighting manufacturers rushing new products to market including the so-called plug-and-play products. Plug and play implies that with power switched off, a fluorescent tube is snapped out of place, the LED lamp with identical bi-pin socket (G13) is snapped into place, power is restored, and the LED lamp instantly illuminates. The manufacturers of 4-ft T8 LED linear lamps have worked hard to match features of the 32W 4-ft T8 fluorescent including output of 1600–2000 lm, greater than 90 lm/W efficacy, ≥80 CRI at warm (3000K, 3500K) and natural white (4000K) CCTs, and a wide enough beam angle to provide uniform light distribution.
"When people test our lamps either alone or in the troffers, we don't want them to perceive worse light or insufficient light; we want it to match their previous experience or be slightly better," said Jeff Hungarter, product portfolio manager at Cree.
Cree recently introduced its LED T8 Series of lamps that deliver 2100 lm output at 21W, 90 CRI, and a 220? beam angle. The lamps are slightly oval in shape (Fig. 4), which provides a portion of the light as uplight (similar to a fluorescent), and are offered in 3500K and 4000K models. Regarding the motivation behind developing a plug-and-play linear LED lamp, Hungarter said, "Many retrofit customers were seeking a simple solution that would not disrupt their workplace and provided an ROI within three years — while improving light and color quality." Because of its performance and five-year warranty, the Cree LED T8 Series meets DLC requirements, enabling eligibility for many regional utility rebates.
Return on investment
Let's discuss ROI. LED linear lamps that produce equivalent light levels and light quality to 32W fluorescents at around 20W will save around 35% in energy costs and some manufacturers are claiming 50% savings.
The DOE performed a detailed lifecycle cost analysis in Report 21.3, comparing a 2×4-ft luminaire with two fluorescent tubes (51W) versus two LED linear lamps (38W), with fluorescent system cost of $30 versus variable LED system cost of $40, $80, or $120 (including driver). While we'll leave the details to the readers to explore, the simulation determined a 2-year or less simple payback if the lamps operate 4,000 hr/year (12 hr/day) and: electricity cost is $0.12/kWh or greater and LED system cost is $40; electricity cost is $0.24/kWh and LED system cost is $80 and it is installed in 15 minutes (not 30 minutes). If the lamps operate only 2,000 hr/yr (6 hr/day), 1-year simple payback is possible at all electricity rates ($0.06–$0.24/kWh) when the system price is $40 and it can be installed in 15 minutes.
Just as the performance evaluation for LED linear lamps should be done on a case-by-case basis, a detailed ROI analysis should also be performed.
The two performance metrics that have long stopped LED linear lamps from competing with fluorescent tubes — comparable light quality and efficacy — are being overcome with today’s highest-performing lamps. As SSL technology continues to advance, LED linear lamps and the expanding lines of plug-and-play lamps will only become more enticing for conversion.
Plug-and-play LED linear lamps provide a convenient and simple option for businesses seeking rapid installation of LED linear lamps. Ballast-bypass approaches are less expensive, but the overall cost is offset by labor installation cost and perhaps disruption to the business environment (the "time is money" effect). LED lamps and drivers (kits) may be preferred when advanced electronic functions are required by the application.
One example of the successful implemen- tation of plug-and-play lamps was realized at an Allstate Insurance office space in Wellington, FL. This facility achieved a noticeable improvement in light quality and realized a 44% energy savings when it upgraded from 4-ft fluorescent tubes to Philips LED T8 InstantFit lamps. LED Source provided the upgrade of 41 tubes utilized in a mix of two-, three-, and four-lamp luminaires.
Tom Neumann, the Allstate representative who was leasing the office space, said he preferred to upgrade the lamps because it was less expensive than other LED upgrades and he now has the option to take the LED lamps with him if he relocates. Energy use from lighting dropped from 3,256 kWh to 1,980 kWh per year, while annual maintenance cost was reduced by $135. Before and after photos of the office (Fig. 5) demonstrate the improvement in lighting quality and consistency with the LED lighting. "My staff is happy because they now have bright lights for better working conditions," said Neumann.
A final consideration with plug-and-play lighting installation techniques involves evaluation of the installed ballast. New high-efficiency instant-start ballasts are priced at $17 and consume less power than older instant-start ballasts, for instance, so a ballast upgrade may be considered and recommended if it is approaching 30,000 hours of use.