I handle cost and material control for a 40-person electrical contractor. The question I hear on almost every commercial lighting retrofit now is “what is the LED equivalent of a 100 watt bulb?” It sounds like a simple lookup. In most cases, it’s a warning sign.
From the outside, replacing a 100-watt incandescent lamp with an LED looks like a no-brainer. Screw it out, screw the LED in, use less electricity. The reality is that the important numbers are lumens, not watts—and in a commercial building, the control circuit matters just as much as the lamp. When either part is ignored, the project stops being cheap.
Client Spotlight: The retrofit where “equivalent” didn’t end with the lamp
A recent retrofit taught me this better than any spreadsheet. A regional warehouse asked us to quote a lighting upgrade. The old fixtures ran on 100-watt incandescent lamps. They also wanted automatic shutoff so the high-bay lights would stop burning all night. Our proposed package centered on an Eaton lighting contactor to switch the high-bay banks, an Eaton light switch at the maintenance entrance as a manual override, and screw-in LEDs to replace the old lamps.
During the pricing call, the facility lead asked, “What is the LED equivalent of a 100 watt bulb?” Their purchasing team had found a 9-watt LED that claimed to be a 100-watt equivalent. It was cheaper than anything on our spec sheet. If I’d looked only at wattage, I would have approved it.
Put simply, a 100-watt incandescent produces about 1,600 lumens. A real LED equivalent should deliver 1,600 lumens, usually at 13–18 watts. The 9-watt lamp they found produced around 850 lumens—basically a 60-watt equivalent with a 100-watt label. The DOE/ENERGY STAR lumen comparison table makes this clear.
We caught that problem in time and switched to a 14-watt LED with test data showing 1,600 lumens. But I treated the rest of the job as a formality. That was the mistake.
What the contactor was actually doing
The old emergency light units were fed from the same lighting circuit we were putting on the Eaton lighting contactor. With a manual switch, that was a slow-burn issue. With an automatic contactor, it became a predictable nightly discharge.
During commissioning, the time clock sent the contactor open to turn off normal warehouse lighting. The emergency light units on that same circuit saw the loss of power and did exactly what they were built to do: they switched to battery. Then they ran until the batteries were low. In the morning, the contactor closed, power came back, and the charging process started over. After several nights, the battery capacity was gone.
When the client ran a 90-minute discharge test, most of the units dropped out after 15 minutes. From the outside, the emergency lights all looked new. The problem was hidden in the switching logic: the controls treated a life-safety backup as an ordinary lighting load.
(I’m not an electrical engineer and I won’t quote code from memory. The relevant requirements are in NEC Article 700 and NFPA 101, and the local AHJ has the final word. The point is: if your emergency light units are downstream of any automatic-off device, get that reviewed by someone qualified.)
The problem is an outdated mental model
Why did this happen? The lighting market still talks in “equivalent wattage.” That phrase made sense when a consumer was choosing one lamp. It fails in a facility because a lighting retrofit is no longer one lamp replacing another. It’s a system. The lamp, the controls, the branch circuit and the emergency lighting path all belong on the same cost sheet.
Energy codes like ASHRAE 90.1 and the IECC—depending on the local jurisdiction—have made automatic shutoff normal. That is a good trend, and we specify Eaton controls on many of those jobs. But it means the question “what is the LED equivalent of a 100 watt bulb?” is no longer sufficient. The old question stops at the lamp. The real question is: “When the controls turn this zone off, what still needs power?”
What that mistake actually cost
The rework cost about $5,000. Maybe $4,800—I’d have to pull the final change order. It required a separate circuit for the emergency units, moving them ahead of the contactor, updating the panel schedule, and another trip for testing.
Compare that to the 9-watt lamp substitution that started the conversation. It would have saved around $1.20 per lamp. On 200 lamps, the purchase-order difference was about $240. We almost created a $240 “saving” that ended in a $5,000 change order. That’s not cost control; that’s cost creep.
What to do about it
Start with the lamp math. A 100-watt incandescent lamp is about 1,600 lumens. A true LED equivalent should deliver 1,600 lumens, usually in the 13–18 watt range. If the package or spec sheet doesn’t list lumens, or lists fewer than 1,600, don’t trust the “equivalent” claim until you see a photometric report.
Then handle the controls as a separate issue. For normal high-bay or parking-lot lighting, an Eaton lighting contactor is a practical way to switch a large load from a low-current control device. Add an Eaton light switch at the entry point for a manual override. That part is straightforward.
The part that needs the most attention: emergency lighting should not be on the controlled side of that same contactor unless the system was designed for it and uses listed emergency control gear. For most battery-equipped emergency light units, an unswitched source is the right answer.
Finally, ask for a control sequence before you request quotes. It can be one page. It should list every zone, mark each as normal or emergency, and say which device turns it off. When you know what stays on after the contactor opens, you won’t have to discover it in a test.
If you still want the LED equivalent of a 100 watt bulb, the answer is 1,600 lumens. The part that costs real money is the wiring behind that bulb.