Your First LED Retrofit Is Now the Baseline: The Engineering Case for a Second One

If your building went to LED somewhere between 2010 and 2016, you made a good call. Compared with the metal halide, high-pressure sodium, or fluorescent systems it replaced, that retrofit cut connected load and took relamping off the maintenance calendar.

That system is now 10 to 16 years old, and the technology has moved a long way since it went in. LED packages, drivers, optics, and thermal design have all improved. The standards utilities use to decide what earns an incentive have been raised more than once. So the useful question today isn’t “LED or not.” It’s how much energy, light, and control capability your existing LED system is leaving on the table.

Where the efficiency gains come from

A luminaire’s efficacy, meaning the lumens it delivers per watt it draws, comes from several efficiencies stacked in series:

Luminaire efficacy = LED source efficacy × driver efficiency × optical efficiency × thermal factor

Every term in that equation has improved over the past decade. Current LED packages produce more light per watt at a given color temperature (CCT) and color rendering (CRI). Drivers waste less power as heat. Lenses and reflectors lose less light. Better heat sinking keeps the LEDs cooler, which helps both output and life. Because the gains multiply, the improvement at the fixture level is bigger than any single component improvement on its own.

The qualification standards show the trend. Under DesignLights Consortium (DLC) SSL V5.1, a high bay has to reach 120 lm/W to be listed as Standard and 135 lm/W to be listed as Premium (DLC SSL V5.1 Technical Requirements). SSL V6.0 raises the efficacy thresholds again, by a 14% weighted average for Standard and 12% for Premium (DesignLights Consortium). And the U.S. Department of Energy’s long-term research goal for complete LED luminaires is 250 to 275 lm/W (U.S. DOE).

To see where your own building stands, pull the rated input watts and initial lumens from the nameplate or the original photometric (LM-79) report. Then account for the hours the fixtures have already run, because output drops over time. If the light you’re actually getting per watt is well below today’s thresholds, there’s a real, measurable energy opportunity.

Power quality and dimming weren’t part of the original spec

Many first-generation specs focused on two things: efficacy and rated life. Today’s qualification requirements ask for more.

On power quality, every luminaire listed under SSL V6.0 needs a power factor of at least 0.9 and current total harmonic distortion (THDi) of 20% or less, measured under worst-case loading (DLC SSL V6.0 / LUNA V2.0 Technical Requirements). That matters in the electrical room. Low power factor and high harmonics increase the current your branch circuits, feeders, and shared neutrals have to carry. The DLC notes that both measurements are commonly at their worst at 277 V (DLC).

On dimming, most indoor luminaires listed as V6.0 Standard must dim continuously to 20% of output or lower. Case, specialty, and hazardous-location categories only have to report their dimming capability. Premium luminaires must dim continuously to 10% or lower and meet the requirements of a DLC controls category above Category 0 (DLC).

Older equipment often falls short here. In a DOE CALiPER evaluation of LED troffers, published in 2013, several products couldn’t be dimmed at all, and some of the dimmable ones flickered when dimmed (U.S. DOE CALiPER). Fixtures like that can’t reliably support the control strategies where most of the remaining savings are.

Lumen maintenance and reliability

DOE recommends defining LED luminaire lifetime as the point when half of a product population has dropped below 70% of its initial output, often written as L70 at B50. The definition is about light output, not about when the fixture stops working (U.S. DOE, LED Luminaire Lifetime). Two things are worth knowing if your system is aging.

First, lifetime ratings are projections. TM-21 projects long-term lumen maintenance from LM-80 test data, and the projection can’t go past six times the test length. With 10,000 hours of LM-80 data, for example, 60,000 hours is the most anyone can legitimately claim (Illuminating Engineering Society). TM-21 also covers only the LED components, not the whole fixture (IES).

Second, the driver often gives out first. DOE research found that driver electronics failures and optical degradation can often happen well before LED lumen depreciation ends a fixture’s life (U.S. DOE).

Put those together, and a system that has run for a decade is likely producing less light than it was designed for. It may show visible color differences from fixture to fixture, and it’s heading into the years when driver failures pick up.

What gets a second retrofit approved

A second-generation retrofit gets approved when the engineering case becomes a financial one. These are the factors that usually carry it:

• Lower connected load for the same light level. The space is redesigned to its target foot-candles instead of swapping fixtures one-for-one at the same wattage.
• Controls you can actually use. Continuous dimming makes high-end trim, occupancy sensing, and daylight harvesting possible. In the DLC’s field study of networked lighting controls, savings averaged 47% across 1,200 monitored zones in 114 commercial buildings (Lighting Controls Academy), though results varied widely from site to site (Minnesota Department of Commerce).
• Incentives with real deadlines. About 70% of commercial lighting rebate programs required DLC listing as of late 2025 (LightNOW). V5.1 listings that weren’t updated to V6.0 come off the Qualified Products List (QPL) on December 15, 2026 (DesignLights Consortium). Many programs also have limited funds that are handed out first-come, first-served (Austin Energy; DTE Energy).
• Less maintenance risk as the installed drivers get older.
• Better light, when the new system is specified for consistent color temperature, low flicker, and glare control.

When a second retrofit may not pay

A second retrofit isn’t automatically the right answer. The case gets weak when fixtures run only a few hours a day, when the existing system was installed recently and already dims smoothly, when measured efficacy is close to current thresholds, or when fixtures are still under warranty. In those situations, adding controls to the existing fixtures, fixing specific problem areas, or waiting for a better incentive can make more sense. The measured baseline in the next article is how you tell the difference.

The other four articles in this series take these factors one at a time and go deeper.

Next step

LED Sales Team can audit your existing LED system, including input power, measured light levels, and dimming capability, and model a redesigned layout against your actual operating hours. Contact us to schedule an assessment.