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some applications, such as corridors and interior parking areas. The 2024 IECC identifies three special applications for occupant sensors, with particular requirements: Warehouse storage areas: The sensor must reduce lighting power by no more than 50 percent within 20 minutes of the area being vacated. Lighting in each aisle must be controlled independently. Lights that are not turned Off by occupant sensors must be controlled via a time-switch enacting scheduling. A manual control must be provided that enables occupants to turn the lighting Off. Open Offices: When a sensor in a control zone detects occupancy, it may turn the lights On to full. When this happens, the lights in unoccupied zones in the open office may stay Off or turn On to no more than 20 percent full power. Within 20 minutes of a control zone being vacated, the lights must turn Off or uniformly reduce to no more than 20 percent of full power. When all occupants have vacated all zones, the control system must turn all general lighting Off, or a timeswitch may be assigned for this. Corridors: Unless the corridor is lighted with the bare amount of illumination required for safety, lighting power must be uniformly reduced by no more than 50 percent within 20 minutes of the space becoming unoccupied.
Time-switch controls (C405.2.2) Where occupant sensors are not installed, time-switch controls must be installed and programmed to automatically turn the lights Off when the space is predictably unoccupied based on a schedule, with notable exceptions. The control must feature a minimum seven-day clock, backup capability in the event of power interruption, and “holiday” programming. New to the 2024 IECC, for spaces where schedules aren’t available, the control system must be programmed to a schedule that turns the lights Off at least 12 hours per day. Users must be given override capability via a manual control device that is limited in zoning to 5,000 sq.ft. and keeps the lights On for no longer than two hours. Manual controls must be located so they are readily accessible to occupants and either enable the lights to be visible or otherwise indicate the area and status of the lights. In certain large facilities such as mall concourses and sports arenas, the override time may be longer (if the override is a captive key device) and the control area may be up to 20,000 sq.ft.
Dimming controls (C405.2.3) Previously titled “light reduction controls,” this section has been thoroughly revised in the 2024 IECC. Eliminating bilevel switching as an option, this version requires continuous dimming controls for general lighting in a list of spaces from classrooms to lobbies to offices (with an exception for lighting controlled by special application controls, which we’ll cover in detail later in this article). Dimming controls must be manual unless high-end trim lighting control is being implemented for the lighting. The lights must be continuously dimmable from full output to 10 percent of full power or lower, plus Off. Again, manual controls must be located such they are readily accessible to occupants and either 50
designing lighting
enable the lights to be visible or otherwise indicate the area and status of the lights.
Daylight-responsive controls (C405.2.4) The 2024 IECC requires that general lighting in daylight zones feature daylight-responsive controls that independently control the lighting, with exceptions. The IECC defines the dimensions of these daylight zones (primary and secondary) based on whether they are sidelit (adjacent to vertical fenestration such as windows) or toplit (under fenestration such as skylights). Daylight-responsive controls are required in daylight zones as defined by the code if the general lighting reaches a wattage threshold, which the 2024 IECC reduced from the 2021 version for primary sidelit and toplit zones. If the space has primary sidelit and/or toplit daylight zones containing more than 75W of general lighting, daylight-responsive control is required. If the total wattage of general lighting in primary and secondary sidelit daylight zones combined is more than 150W, again, control is required. The lighting in sidelit and toplit zones must be controlled independently, as must lighting in primary and secondary sidelit zones. In the 2024 version of the IECC, the calculated exception to daylight-responsive controls in trade for lowering the lighting power allowance was removed, and an exception added for enclosed office spaces smaller than 250 sq.ft. Controls must be automatic and provide continuous dimming down to at most 15 percent of full light output and be capable of turning the lights Off. Controls must be configured so they can be calibrated within the space, with the calibration means readily accessible. In warehouse storage areas and corridors where occupant sensing reduces lighting, daylight-responsive controls may reduce power further but not raise it above the level set by the occupant sensor.
Special applications (C405.2.5) The 2024 IECC designates control requirements for special applications such as display and accent lighting and supplemental task lighting. These luminaires must be controlled by either an occupant sensor or time-switch control for automatic shutoff, plus a manual control enabling them to be controlled separately from the general lighting. Lighting for nonvisual applications such as plant growth must be served by an independent time-switch control. However, note that Section C405.4 in the 2024 IECC calls out horticultural lighting and states that the luminaires in greenhouses must be controlled by a device that turns Off luminaires in response to daylight.
Interior parking garage lighting controls (C405.2.9) The 2024 IECC requires lighting controls in interior parking garages. Interior parking garage lighting must be controlled by either an occupant sensor or a time-switch control. Additionally, lighting power must be automatically reduced based on occupancy with a time delay of 20 minutes and a control zone limited to a maximum of 3,600 sq.ft. At entrances and exits where lighting is provided for visual adaptation between indoor and outdoor brightness levels, this lighting must be reduced by at least 50 percent between sunset to sunrise.
Sleeping and dwelling unit controls (C405.2.10) The 2024 IECC created a new special section for sleeping