Judge a lighting retrofit on functional fit first. Ask whether the proposed lighting will still serve the work done in the space. The proposal should document the light each area needs, show measured light levels for the existing setup, and spell out which fixtures, controls, and related work will change.
Only after that does it make sense to compare operating hours, energy use, and dollar payback. A solid lighting retrofit assessment treats any payback figure as provisional until its schedules, project costs, and utility rate assumptions are written down.
Start With the Space's Tasks and Measured Light
The first gate is simple: does the proposal document both sides of the light-level comparison? You need what each area needs and what each area has today. In a DOE/PNNL field evaluation of advanced lighting control systems at five sites, the authors recommend determining site-specific light level needs and measuring existing light levels to support cost-effectiveness calculations.
Fixture wattage can't answer this question. Wattage is the power a fixture draws. It doesn't tell you how much light reaches a workbench, a packing table, or a shelf face. Use this table to sort what the proposal gives you:
| Review item | Evidence to request | Next action |
|---|---|---|
| Task needs | Proposed light levels per task area, with their basis | If missing, ask the proposer to define them by area |
| Existing conditions | Measured light levels in those same areas | If only estimated, request on-site measurements |
| Side-by-side match | Proposed vs. measured values, area by area | If areas don't line up, pause the payback review |
When all three rows are filled in, you can tell whether the proposal documents a real before-and-after comparison. That is a review result, not a design approval. The PNNL recommendation comes from five evaluated sites and doesn't set a universal light level, so the right target still depends on your tasks. If you want to take or check measurements yourself, DOE's indoor environmental quality assessment guide describes three approaches: monitors, the lumen method, and simulations. It also notes that a simulation provides only an approximation.
Spaces with mixed activity need this check zone by zone. Our guide to warehouse task zones shows how picking and packing areas can call for different planning than storage aisles.
Check the Project Scope and Control Changes
Next, pin down exactly what the project changes. A fixture-only swap and a project that also replaces controls raise different questions, and they can carry different installed costs. Ask the proposal to state:
- Fixtures: which ones are replaced, retained, or added, with type, model, and quantity per area. This applies whether the quote draws from our commercial lighting collection or another source.
- Controls: whether switches, occupancy sensors, dimming, or schedules change.
- Control-system electronics: which new sensors, controllers, or dimming components are proposed, and which existing ones stay.
- Related site work: any associated work the quote includes, and anything it leaves out.
When control electronics change, ask how compatibility will be tested. The same PNNL report recommends that any proposed new system be tested for compatibility with existing and new system electronics. A product label or spec sheet alone doesn't settle that for your building. Until the proposer shows project-specific compatibility evidence, treat any savings that depend on those controls, such as reduced hours from sensors, as unresolved. Wiring, circuit design, and code-compliance decisions belong to a licensed electrician, the project designer, or your local authority, not to this review.
If the quote substitutes a different fixture or control than the one originally specified, a substitution equivalence matrix helps you check photometry, mounting, and controls together.
Make Existing and Proposed Energy Inputs Comparable
An energy-use comparison is only fair when both cases are documented in the same terms. Keep two separate records instead of assuming the new system will run on the old schedule.
For a reference point, DOE's park-lighting retrofit workbook lists audit steps that include identifying lamp types and wattages, counting lamps per fixture, and estimating average time of use. It then estimates energy use for each application. The workbook was written for park facilities, so use it as an example of records to request, not as a complete method for your project. A practical request list looks like this:
- Existing case: fixture or lamp type, wattage, quantity per area, and actual operating hours, with where the hours came from (logs, meters, or staff estimates).
- Proposed case: fixture type, wattage, quantity per area, and the proposed operating schedule.
- Control assumptions on each side: any sensor, dimming, or schedule effect the estimate counts, and whether it depends on the compatibility evidence above.
- Status flag: each entry marked verified or provisional.
Schedules deserve their own line. In DOE's guidance on K-12 energy-savings performance contracts, operating hours matter to savings baselines and post-retrofit calculations. The same guidance says a permanent schedule change may require a baseline adjustment that can affect project financials and total payback period. Outside that contract setting, the lesson for your review is simple. If hours differ between the two cases, the proposal should say so and explain why.
If any proposed wattage, schedule, or control entry is still provisional, the energy comparison built on it is provisional too.
Separate Energy-Use Savings From Financial Payback
Energy use and payback answer different questions. An energy comparison asks how much electricity the proposed lighting would use compared with the existing setup, while a payback estimate asks how long it takes to recover project costs in dollars. That second question adds two more inputs, project costs and energy prices, that each need their own documentation.
Start with the cost boundary. Ask which costs the payback figure includes: fixtures, controls, labor, and any associated site work. Two estimates that count different work will produce payback numbers that can't be compared, even when their energy figures match. Before you compare their numbers, a lighting quote scope check helps confirm that two quotes cover the same work. If an estimate counts an incentive, ask which program it assumes and whether eligibility has been confirmed for your project.
Then check the energy price. U.S. electricity rates depend on your utility and the service you buy, so the estimate should name the utility service and tariff it uses. You can then compare that against your own bills. Future prices matter too. In DOE's K-12 primer, energy-cost escalation estimates should come from utility bills, utility input, and historical and local data, because those projections affect projected payback.
If the cost scope, the rate basis, or the calculation method isn't documented, label the payback estimate provisional. Don't treat its duration as a decision-ready number. A useful lighting retrofit assessment ends with a clear list of which inputs are confirmed and which are still open.
FAQs
Does lower fixture wattage mean a retrofit will work for the space?
No. Lower wattage means the fixture draws less power. It says nothing about how much light lands on the work surface or how that light is spread across a task area. Fit is a separate question, answered by comparing proposed light levels with measured existing levels for each area. A lower-wattage fixture can pass or fail that comparison.
Do existing and proposed operating hours need to be the same?
Not necessarily. Hours can differ for legitimate reasons, such as occupancy sensors or a planned schedule change. What matters is that each case lists its own hours, states where they came from, and explains the difference. A proposal that quietly reuses the old hours for the new system, or assumes reduced hours without explaining why, leaves the energy comparison unverified.
Which electricity rate should a U.S. payback estimate use?
Use the rate that applies to your own utility service and tariff, as shown on your bills. A generic national average or a rate from another utility can push the estimate in either direction. Ask the proposer to name the utility, the tariff, and whether the estimate assumes future price changes.
Is a provisional payback estimate still worth having?
Yes, as a screening tool. It can show whether a project is worth a closer look. Keep the provisional label attached, and list the open inputs, such as unmeasured light levels, untested controls, or an unnamed tariff. Then update the estimate as each one is confirmed. Just don't use it to make the final decision until those inputs are confirmed.
