Lighting Layout in a Sloped-Ceiling Manufacturing Bay
A 24,000 sq ft manufacturing bay has a 32-foot ridge with a 4:12 slope on both sides. The lighting design calls for 96 high-bay LED fixtures in a 12 by 8 grid, mounted 24 feet above finished floor, with emergency units on the same circuit as general lighting. The architect requires fixtures to be hosted to the roof structure so they remain perpendicular to the slope. Your modeler placed fixtures on the level's reference plane, so they appear level in plan but the sections show them horizontal, not perpendicular to the roof. The electrical engineer also wants to split the bay into two lighting control zones by aisle.
1. Explain the modeling consequence of placing fixtures on the level reference plane versus hosting to the sloped roof, and how to correct the layout without losing circuit assignments.
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Fixtures placed on a level reference plane have a work plane parallel to the floor. They will appear correct in plan but will be horizontal in section, so their photometric distribution is wrong relative to the sloped ceiling and the architect's perpendicular requirement is unmet. Hosting to the roof face sets the fixture's work plane to the sloped surface, so the fixture rotates with the slope and section views read correctly.
Correcting this without losing circuits: do not delete and re-place. Select the fixtures, use Pick New Host or set the work plane to the roof face, and re-place while preserving the existing circuit. Revit generally retains circuit membership when a device is rehosted, but verify in the System Browser and panel schedule afterward. If rehosting breaks circuits, reassign by selecting the circuit in the System Browser and using Edit Circuit to add the fixtures back.
Before rehosting, confirm the roof is a single face or that the fixtures are grouped by slope side, and check that the fixture family's light source definition is oriented to the family's host face, not a fixed direction.
2. The engineer wants two lighting control zones by aisle and emergency units on the general lighting circuit. Identify the circuiting risks and how you would structure circuits and switches.
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Two risks arise. First, if emergency units share a circuit with general lighting, a single breaker trip or switched leg de-energizes emergency illumination. Code and good practice typically require emergency illumination on a separate circuit or an approved emergency circuit so that general lighting failure does not remove egress lighting. The engineer's direction should be challenged and resolved before modeling.
Second, splitting by aisle means circuits must be organized by physical zone, not by modeler convenience. If circuits are created by selecting fixtures in a plan window, sloped geometry can cause missed or double-selected fixtures.
Approach: define two switch systems, one per aisle zone, and assign fixtures to circuits by zone. Use the System Browser to verify fixture counts per circuit against the design. Keep emergency units on a dedicated emergency circuit with its own breaker and, where required, a separate emergency panel or generator-backed source. Add circuit descriptions and zone names as parameters so the panel schedule reads clearly, and coordinate the switching arrangement with the architect's control intent.