Ask a lighting designer for an updated photometric comparison when your change alters the lit area's coverage geometry, moves or re-aims fixtures, or changes the task the light has to support. A replacement fixture with a different name or model number does not settle the question either way.
What matters is whether the old plan still describes the site you are about to build. Treat the design comparison as a separate question from local permitting: your designer checks the lighting assumptions, and the local authority decides whether a new plan or permit submittal is required.
When Should You Request an Updated Photometric Review?
Request a designer's comparison when a proposed change alters coverage, fixture placement or aiming, or the task being served. This table is a practical planning rule for outdoor lighting projects, not a code threshold.
| Proposed change | Recommended next move |
|---|---|
| Lit area, coverage boundary, or served task changes | Request a designer comparison with the prior plan |
| Fixture location, mounting condition, or aiming changes | Mark the changes and request a comparison |
| Only the replacement label changes | Compare photometric data and configuration first |
A photometric plan is a model built from specific inputs: site dimensions, fixture heights and locations, each fixture's light distribution, aiming, and the light levels the application calls for. When one of those inputs changes, the plan's results no longer describe the real site. That is why the change itself, not the product name, drives the decision.
When Coverage Geometry Changes
Start by laying the prior plan over the proposed site layout. A new parking row, an expanded drive aisle, a removed building wing, or a moved property-line boundary all change the shape of the area the plan was built to cover. Flood and area fixtures also spread light in different patterns, so coverage shape differences matter when evaluating LED area light layouts as boundaries move. If the intended coverage is no longer what the old plan modeled, ask the designer to rerun the comparison against the new outline.
When Fixture Positions or Aiming Change
Moving a pole, changing a mounting height, adding a fixture, or tilting a head changes where light lands, even if every fixture keeps the same model. Plans record these details for a reason. As one local example, the Buncombe County lighting plan checklist calls for point-by-point footcandle photometrics showing exterior fixture locations and aiming at the developed area and property lines. Spacing changes can also open dark gaps, a risk covered in our guide to perimeter fence lighting layouts. Mark every moved, added, removed, or re-aimed fixture and ask for a comparison.
When the Served Task Changes
A lot that once handled overnight employee parking may now host evening customer pickup. A storage yard may become a loading area. When the activity changes, the light levels and coverage the original designer targeted may no longer fit. Describe the old use and the new use in plain terms, then ask the designer whether the prior lighting assumptions still apply. Leave the target light levels to the designer instead of picking numbers yourself.
When Only the Replacement Label Changes
A new label tells you very little. Two fixtures with different names can have similar photometric behavior, and two with similar names can distribute light very differently. Compare the replacement's available photometric documentation, distribution type, and configuration settings (such as selectable wattage or optics in an area light with shortcap) with what the existing plan assumed. If those inputs match the plan, you have a documented basis for the swap. If they differ, or the old plan does not record them, request a designer comparison.
What Should You Send With a Review Request?
Send the designer enough to see the existing project and the proposed change side by side. Keep existing conditions and proposed changes on separate sheets or layers so the differences are easy to spot.
- Prior plan and records: the previous photometric plan plus any related approval or submittal records you can locate.
- Current conditions: a site layout showing existing fixture locations, mounting heights, and aiming. Our retrofit documentation checklist covers what to photograph and measure.
- Marked proposed changes: new, moved, removed, and re-aimed fixtures, plus any change in mounting conditions or site dimensions.
- Areas and tasks served: each area by name, with its use before and after the change.
- Fixture documentation: whatever photometric files, spec sheets, and configuration details are available for the proposed replacement.
If the original plan is missing, say so at the start instead of letting the designer assume a baseline exists. Provide the best current-condition layout you have and ask what kind of comparison it can support. Gaps like an unknown mounting height or an undefined task can stall the work, so check for missing lighting project inputs before you send the package.
Who Confirms Local Review and Permit Requirements?
Two different parties answer two different questions. A lighting designer or engineer compares your changed lighting inputs with the existing plan and tells you whether the design still holds up. The planning or permitting authority for the property's location decides whether the change needs an updated plan, a resubmittal, or a permit.
Local rules can turn on details that have nothing to do with design quality. In Madison, Wisconsin, the city's outdoor lighting plan requirements ask photometric plans to show light distribution in a footcandle grid and the locations of all new and existing fixtures. Madison also sets compliance scope under MGO 29.36 by fixture count. If more than 50% of total fixtures are added or changed, the entire site must meet MGO 29.36. Below that share, only the new fixtures must comply. That percentage is a Madison compliance rule. It is not a general trigger for requesting a design review, and it does not carry over to other cities or counties.
To find your own authority, start with USAGov's local government directory, which lists city and county contacts by state. Ask that office which department handles exterior lighting plans and whether your marked changes require a new submittal.
FAQs
Does a new design comparison mean I have to resubmit my lighting plan?
No, not by itself. The designer's comparison tells you whether the lighting still works as planned. Whether a resubmittal or permit is needed is a separate decision made by the local planning or permitting office, so ask them directly.
Does Madison's 50% fixture-change rule apply in other places?
No. Madison's distinction applies to compliance scope under its own ordinance, MGO 29.36. Other jurisdictions set their own rules, which may use different thresholds or none at all. Confirm the rule with the authority where your property sits.
What if nobody can find the original photometric plan?
Tell the designer up front that the baseline plan is missing. Then supply a current-condition layout with fixture locations, mounting heights, aiming, and the uses of each area. The designer can tell you what comparison those records support and what still needs to be measured.
Can my project team compare the replacement fixture without a designer?
Your team can compare documented facts: fixture locations, mounting heights, aiming, and the replacement's photometric files and configuration against what the old plan lists. Whether the result still meets the project's lighting goals, or any code requirement, is a conclusion for a lighting designer, engineer, or the local authority.
