2021 IECC Section C405.2
Lighting controls make sure lights are off when nobody needs them and dimmed when daylight or a task allows. Section C405.2 of the 2021 IECC sets the controls, and the inspector checks them in the field: sensors that turn lights off, time switches with the right features, dimming for daylight near windows, and separate switching for display and task lighting. Lesson 10 covers how much lighting power is allowed. This lesson is about how it is controlled. Local adoption governs which edition applies (Lesson 1).
C405.2 gives two ways to comply. The first is the set of controls in C405.2.1 through C405.2.7. The second uses luminaire-level lighting controls, where each luminaire can sense occupancy, dim when the space is empty, sense daylight and electric light to hold a target level, and be tuned for setpoints, time delays, and zoning, plus the sensor, specific-application, and manual control rules. Not covered: security and emergency areas that must stay lit, interior exit stairways, ramps, and exit passageways, and normally-off emergency egress lighting.
C405.2.1 lists the spaces that need occupant sensors: classrooms and training rooms, conference and multipurpose rooms, copy and print rooms, lounges and breakrooms, enclosed offices, open plan offices, restrooms, storage rooms, locker rooms, corridors, warehouse storage areas, and any other space of 300 square feet or less enclosed by floor-to-ceiling partitions. Under C405.2.1.1 the sensor must turn lights off within 20 minutes after everyone leaves, the lights must come on by a manual switch or automatically at no more than 50 percent power, and occupants must have a manual control to turn lights off. Full automatic-on with no manual control is allowed in corridors, interior parking areas, stairways, restrooms, locker rooms, lobbies, library stacks, and places where manual operation would endanger safety or security.
An open plan office under 300 square feet follows the general rule. A larger one (C405.2.1.3) is divided into control zones of no more than 600 square feet. A zone may come on automatically when occupied, other zones may stay off or come on to 20 percent of full power or less, and each zone must turn off or drop to 20 percent or less within 20 minutes after occupants leave it. In a warehouse (C405.2.1.2) each aisleway is controlled separately and drops to 50 percent or less within 20 minutes of vacancy, with a time switch turning off what the sensors do not. Corridor sensors (C405.2.1.4) reduce lighting to 50 percent or less within 20 minutes, except corridors with under 2 footcandles at the darkest floor point with all lights on.
Any area without a compliant occupant sensor needs a time switch (C405.2.2), except luminaires with specific application controls, patient care spaces, spaces where automatic shutoff would endanger safety or security, lighting meant to run continuously, and shop and laboratory classrooms. A time switch (C405.2.2.1) has a 7-day clock with seven day types, an automatic holiday shutoff of at least 24 hours, and at least 10 hours of program backup. Its override switch is manual, keeps lights on for no more than 2 hours, and serves no more than 5,000 square feet. In mall concourses, auditoriums, sales areas, manufacturing facilities, and sports arenas a captive key override may run longer, over an area under 20,000 square feet.
Where there is no occupant sensor, general lighting also needs a manual light-reduction control (C405.2.3) that cuts the load by at least 50 percent evenly, by continuous dimming to under 20 percent, by switching to 30 to 70 percent power, or by switching alternate luminaires or rows. Exceptions include daylight-controlled luminaires, and, with a manual control, a space with one luminaire under 60 W, spaces under 0.45 W per square foot, and corridors, lobbies, electrical rooms, and mechanical rooms.
C405.2.4 requires daylight-responsive control of general lighting in a space that has more than 150 W of general lighting in its primary sidelit zones, more than 300 W in its sidelit zones, or more than 150 W in its toplit zones. Exceptions include patient care spaces, sidelit zones on the first floor in Groups A-2 and M, and new buildings whose connected lighting power is not greater than the adjusted allowance from Equation 4-9. Under C405.2.4.1 the controls must dim continuously from full output to 15 percent or lower and be able to shut lights off; toplit and sidelit lights, and primary and secondary zone lights, are controlled separately; sidelit zones facing different cardinal orientations are controlled independently (with up to 150 W allowed to be combined per space); the controls must be calibrated from inside the space; and if an occupant sensor has dropped lights to an unoccupied setpoint, daylight control may not raise them above it.
A sidelit zone (C405.2.4.2) is the floor area beside a wall window. The primary zone reaches into the room up to 1.0 times the height from the floor to the top of the window, and beyond each edge of the window along the wall up to 0.5 times that height, stopping at any full-height wall; the secondary zone lies behind it, out to 2.0 times the head height. A window creates a zone only if it is at least 24 square feet, its visible transmittance is at least 0.20, nothing blocks daylight closer than half the height from the window bottom to the top of the obstruction, and any overhang has a projection factor of no more than 1.0 (north) or 1.5 (other orientations). A toplit zone (C405.2.4.3) extends beyond a skylight up to 0.7 times the ceiling height, and the skylight's visible transmittance times its opening area divided by the zone area must be at least 0.008.
Worked example. A Houston office wall has a window 8 feet wide and 4 feet tall with its top 8 feet above the floor, so head height is 8 feet. The window is 32 square feet, which is over 24. The primary zone is 8 feet deep (1.0 x 8) and extends 4 feet (0.5 x 8) past each edge, so it is 8 + 4 + 4 = 16 feet wide, or 16 x 8 = 128 square feet if no wall interrupts it. The general lighting in that primary zone totals 180 W, which exceeds 150 W, so daylight-responsive control is required unless an exception applies. The secondary zone reaches to 16 feet from the wall.
Display and accent lighting, display case lighting, supplemental task lighting such as under-cabinet lights, and lighting for sale or demonstration need an occupant sensor or time switch plus a manual control separate from the general lighting (C405.2.5). Sleeping units switch off all permanently installed luminaires and switched receptacles within 20 minutes after occupants leave, unless card-key controlled. Manual controls must be readily accessible and located where the lights are visible or labeled with the area and status (C405.2.6). Exterior lighting (C405.2.7) needs daylight shutoff, and facade and landscape lighting must turn off from no later than 1 hour after closing to no earlier than 1 hour before opening. Other exterior lighting cuts wattage by at least 50 percent at a set time or after 15 minutes without activity, and parking luminaires over 78 W mounted 24 feet or lower drop 50 percent after 15 minutes without activity, with no more than 1,500 W controlled together. Parking garage lighting (C405.2.8) drops by at least 30 percent after 20 minutes without activity in zones of 3,600 square feet or less.
In the field
GCHS is reviewing a lighting retrofit for a community center with a large open room, two classrooms, a lobby, and a south wall of windows. On the plans the reviewer looks for a sensor symbol in every classroom, the open room split into control zones of 600 square feet or less, a time switch for the lobby, and separately switched lights along the window wall. In the field the inspector walks in, waits for the lights to drop, checks that the daylight sensor is not aimed at a light fixture and can be calibrated, and confirms the override button on the time switch is a 2 hour one. Alteration rules for existing buildings come in Lesson 13.
1. An inspector reviews a new Group B building with a 240 square foot enclosed private office that has a wall switch only. What does C405.2.1 require for this office?
2. How long may an occupant sensor in a Group B conference room wait after the last person leaves before it must turn the lights off, under C405.2.1.1?
3. A 20 foot by 15 foot Group B conference room has a sensor that turns the lights on automatically when someone enters. What limit applies to automatic turn-on under C405.2.1.1?
4. Which space may use full automatic-on lighting with no manual control under the exception to C405.2.1.1?
5. A Group B building has a 1,200 square foot open plan office controlled by occupant sensors. What is the largest floor area of one lighting control zone under C405.2.1.3?
6. When a person enters one control zone of a large open plan office, what may the general lighting in the other unoccupied zones do under C405.2.1.3?
7. An occupant sensor in a Group B corridor with 6 footcandles at the darkest point (all lights on) is reducing lighting when the corridor is empty. To what level must it reduce lighting power within 20 minutes under C405.2.1.4?
8. The override switch on a time switch that controls lighting in a Group B office allows the lights to stay on for how long at most under C405.2.2.1?
9. An inspector finds one time-switch override button controlling 8,000 square feet of open office lighting in a Group B building. What is the finding under C405.2.2.1?
10. Which feature is required of a time switch under C405.2.2.1?
11. A Group B office space has 130 W of general lighting in its primary sidelit daylight zone and 180 W in its secondary sidelit zone, and no exception applies. Is daylight-responsive control required under C405.2.4?
12. Under C405.2.4.1, daylight-responsive controls must be able to dim lights continuously from full output down to what level or lower?
13. An inspector measures a window 8 feet wide and 4 feet tall with its top 8 feet above the floor in a Group B office. No full-height wall is closer. How deep is the primary sidelit daylight zone under C405.2.4.2?
14. Which window would not create a sidelit daylight zone because of its size or glass under C405.2.4.2?