A perfectly balanced drawing can still mark the wrong place to drill. In this office renovation, an AI-generated layout produced a useful starting line for three recessed lights, but an inspection above the ceiling revealed building-service piping in the proposed path. The entire three-light pattern had to move together before any 75 mm holes were made.
This field case from Goyang, Gyeonggi Province, shows how I used measured dimensions and ChatGPT to explain a lighting layout before drilling—and why the final decision still depended on an electrician checking the real ceiling.
It distributes a predetermined number of lights evenly along one straight run, using an end offset equal to half the center-to-center spacing. It does not calculate the required illuminance or determine how many lights a room needs.
Project at a Glance
1. Measuring the Available Run
The customer considered the office too dark and requested three additional recessed lights. The quantity had already been selected, so my immediate task was not to perform a complete photometric design. It was to arrange those three points evenly within the measured run and communicate the proposal clearly before drilling.
For a lighting design that must meet a specified lux level, additional information would be required: luminaire output and photometric data, mounting height, beam distribution, room reflectance, work-plane height, daylight, furniture, and the intended visual task. Those data were not recorded for this field case.
2. Calculating an Even Three-Light Pattern
When the end margin is set to one-half of the center spacing, the measured length can be divided by the number of lights:
Measured from one end of the 2,420 mm run, the theoretical light centers were approximately 403.3 mm, 1,210.0 mm, and 2,016.7 mm. In the field, marks may be rounded sensibly, but the total dimension should be checked rather than rounding every segment independently and accidentally adding or losing length.
The image showed visual balance, but it did not know the positions of piping, ducts, T-bars, framing, sprinklers, diffusers, or electrical conduits. Those conditions had to be inspected at the site.
3. Why the Entire Layout Moved
Before drilling, the ceiling space was checked and building-service piping was found where the proposed openings would have been made. Drilling on the original line could have damaged the piping or left too little clearance for the recessed-light openings and wiring.
Instead of moving only one light and destroying the rhythm of the row, all three points were shifted together by the width of one ceiling tile. This preserved the calculated spacing between the lights while relocating the complete pattern away from the obstruction.
If an obstruction affects a straight row, moving the entire set by the same amount can preserve center spacing and visual balance. The revised points still require individual clearance checks before drilling.
4. Drilling and Electrical Work Scope
After the revised locations were checked, three 75 mm openings were made and the power wiring was prepared for the future luminaires. My electrical work ended at that stage. The interior contractor had chosen to provide and install the actual light fittings separately.
For that reason, this article does not claim a luminaire wattage, color temperature, beam angle, final illuminance, completed installation, or successful lighting test. Those details were outside the recorded scope of my work.
A General Formula for This Layout Rule
For a straight run of length L containing N equally spaced light centers, with each end offset equal to half the center spacing:
The center of light number i, measured from the starting end, is E + (i − 1)S. This is a geometric layout convention, not a substitute for lighting design, product instructions, or site inspection.
Simple Example — Four Lights Across 2,400 mm
Suppose four lights will be arranged evenly across a straight 2,400 mm run.
Center spacing: 2,400 mm ÷ 4 lights = 600 mm
End offset: 600 mm ÷ 2 = 300 mm
300 mm
900 mm
1,500 mm
2,100 mm
The first light starts 300 mm from the beginning. Each following light is positioned at 600 mm center-to-center, leaving the same 300 mm offset at the opposite end.
Frequently Asked Questions
Does this formula tell me how many recessed lights I need?
No. It evenly positions a quantity that has already been selected. Determining quantity requires lighting-output and room-design information that was not available in this case.
Can the same method be used for four lights?
Yes, if the design goal is one straight row with half-spacing at both ends. For a 2,420 mm run, the center spacing would be 605 mm and each end offset would be 302.5 mm. Rounding both ends to 303 mm would create a 2,421 mm total, so the field marks must be reconciled with the actual length.
Why not move only the obstructed light?
Moving one point would change the center spacing and could make the row look uneven. Because the available ceiling allowed it, all three points were moved together by the same amount.
Did AI determine the final drilling locations?
No. AI helped calculate and visualize the initial proposal. The electrician determined the final locations after inspecting the ceiling and identifying the piping conflict.
Field Conclusion
AI made the initial spacing calculation easier to visualize and helped explain the plan before work began. Its most valuable role was communication—not authority. The generated layout could not inspect the void above the ceiling or accept responsibility for a drilling decision.
The practical lesson was simple: calculate first, inspect second, and drill only after the drawing and the physical site agree.
Document ID: EK-018
Published: July 29, 2026
Electric Korea
Korean Electrical Construction · Field Experience · Safety · Technical Education
Website: electrickorea.co.kr
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