Strobe candela &
spacing calculator.
Compare candela, mounting, and placement for a room—not just a hallway.
Example device setting for one centered wall strobe in a 40 × 30 ft room; reference output 60 cd. Change the inputs to compare layouts.
Illustrative plan view. The shaded region is the modeled room or grid cell, not a photometric contour.
What makes the room count
A 30 × 30 ft room can require 34 cd from a single wall strobe. A 30 cd device setting is below that reference minimum; choose the next suitable listed setting. A centered ceiling strobe uses a different, mounting-height-dependent reference.
Compare the arrangement
Wall mode compares one centered appliance with a four-wall arrangement. Ceiling mode supports a centered device, an offset device, or a grid based on your chosen candela. Corridor mode applies the manufacturer’s straight-corridor reference separately.
How the reference lookup works
For room sizing, the larger dimension selects the enclosing square. An offset ceiling device uses twice its greatest perpendicular distance to a wall. Heights round up to the next 10, 20, or 30 ft reference band; values are never interpolated.
Ceiling mode uses conservative manufacturer reference sizes of 20, 30, 50, and 70 ft, plus verified 40 ft and 44 ft rows at heights up to 10 ft. It may select a higher candela than a fuller code table. Values are planning references, not a certification of compliance.
Before using the layout
Confirm the adopted NFPA 72 edition and actual appliance listing. This planner excludes sleeping rooms, irregular spaces, obstructions, and performance-based designs. It does not evaluate audibility or intelligibility. Review synchronization, circuit capacity, and voltage drop separately. A grid or multiple wall appliances require coordinated synchronization as applicable.
View manufacturer references
Potter wall-mount installation reference, Table A
System Sensor application guide, January 2015, Sections 5–7
Potter ceiling-mount installation reference, Table A
These manufacturer references cite earlier NFPA editions. Verify the requirements in force for your project before final selection.
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Common questions
What is the difference between required candela and a selectable device setting?
The reference output is a design lookup; a device offers specific listed settings. Select an available setting at or above the applicable requirement. A 34 cd requirement is not satisfied by a 30 cd setting.
Why can wall and ceiling strobes need different candela?
Their placement and light distribution are evaluated differently. Ceiling selection also depends on mounting height and distance to the walls. Do not reuse a wall setting automatically for a ceiling appliance.
Does adding up the candela of several strobes prove coverage?
No. Location, arrangement, listing, and applicable spacing criteria still govern. The planner compares specific arrangements rather than treating candela as an area total.
Does the calculator check audible notification too?
No. Its room and corridor calculations address visible notification planning. Sound pressure, ambient noise, frequency requirements, and speech intelligibility need separate evaluation.