Okay, that's a good question, and the ambiguity in the wording is understandable. Based on industry practice and the intent of emergency lighting, here's the likely interpretation of "measured along the path of egress"

"Measured along the path of egress" means along the actual path people would use to exit, taking into account the required width of the egress path.

Here's a breakdown of why: Practicality and Intended Use

Emergency lighting is intended to allow safe evacuation. People don't evacuate along a single, infinitely thin line. They evacuate within a corridor, hallway, or stairway. The lighting needs to adequately illuminate the entire width of that escape route.

Minimum Illumination Requirement

The .1 foot-candle minimum requirement is key. If you only measured along a theoretical center line, you could have a spot on the edge of the egress path that is dangerously dark, even if the center line passes the .1 fc test.

Photometric Maps

The very fact that they're asking for a photometric map indicates they want to see the light levels across the entire area of the egress path, not just a line. A map shows the distribution of light.

Code Intent

The core concept of egress is to provide a safe, unobstructed pathway out of a building. An area that is not sufficiently lit is not safe.

How to Interpret the Requirements for Your Photometric Plan

Here's how to approach meeting the requirements of the comments:1.

Define the Path of Egress

Accurately determine and clearly indicate the exact path of egress on your plans. This includes the width of corridors, stairways, and any other part of the escape route. This should be based on your architectural drawings and code requirements for egress width.2.

Create the Photometric Grid

Your lighting design software will create a grid for analysis. Your photometric map will show the light levels at points across the path of egress at floor level. The grid points shouldn’t be too spaced out so you don’t miss a dim point.3.

Analyze the Results



Average Illumination

Calculate the average foot-candle level across the entire area of the egress path. This average must be at least 1 foot-candle.

Minimum Illumination

Examine the photometric map carefully. Make sure that at every point within the egress path (that falls within your grid) you have at least 0.1 foot-candle. The key word is "any point".
4.

Adjust Lighting as Needed

If you don't meet both the average and minimum requirements, adjust your lighting design (number of fixtures, type of fixtures, placement of fixtures) and re-run the photometric analysis.5.

Submit the Photometric Map

Your photometric map should visually show the foot-candle levels throughout the egress path, making it clear that you meet both the average and minimum requirements. Include a legend so the reviewer can easily interpret the color-coding of the map.

In summary, focus on providing uniform lighting across the width of the egress path, ensuring both the average and minimum illumination requirements are met across that area. Do not take "path of egress" to simply mean a single line.Important Considerations



Local Code Official

While the above is a general interpretation, it's ALWAYS best to confirm this interpretation with your local building code official or the person who made the comment. Ask for clarification if you're unsure. A quick phone call or email can save you significant time and rework. Say something like, "To ensure we're meeting the requirements, we're interpreting 'measured along the path of egress' to mean that the 0.1 foot-candle minimum must be met at every point within the entire width of the egress path. Is that correct?"

Software Defaults: Be careful of default settings in your lighting design software. Make sure it's set up to calculate light levels at the correct height above the floor and that the grid spacing is appropriate for your application.By clarifying with the code official and focusing on area illumination rather than just a line, you'll have a much better chance of getting your permit approved. Good luck! Flag for review