Lighting control requirements: What's current and what to expect
This article examines lighting control requirements in various codes and standards, commissioning these controls, and what engineers may expect in the future.
- Learn which codes dictate lighting controls and requirements.
- Understand the different lighting controls available for various applications.
- Understand compliance and functional testing requirements.
Energy codes require lighting engineers to design lighting systems that meet prescribed power allowances, use daylighting controls, control spaces through occupancy, and specify and perform functional testing in their lighting designs. ANSI/ASHRAE/IES Standard 90.1 and the International Energy Conservation Code (IECC) are the two most prevalent energy codes governing lighting, with some states having specific energy codes. This article examines lighting control requirements in various codes and standards, commissioning these controls, and what engineers may expect in the future. ASHRAE 90.1–2010 and IECC-2012 will be the focus.
ASHRAE and IECC both require spaces surrounded by ceiling height partitions (walls) to have an individual manual control (switches/dimmers). The control must be within the space or remote located with an indicator that identifies the space/area it serves. Exemptions to this requirement are for areas that must be continuously illuminated for safety/security and corridors or stairways used for means of egress.
In addition to the above requirement, light reduction is required.
ASHRAE 90.1 Section 126.96.36.199a requires a control step between 30% and 70%, which can be accomplished with a number of variations such as switching alternating lamp, dimming ballast/driver, or stepped ballast/driver. IECC-2012 Section C405.2.1.2 requires a control step of 50% with even illumination in the space and offers specific ways to accomplish this by controlling all lamps or luminaries; dual switching alternate rows of luminaries, alternate luminaries, or alternate lamps; switching the middle lamp luminaries independently of the outer lamps; or switching each luminaire or each lamp.
Exceptions to 188.8.131.52a are:
- Lights in corridors, electrical/mechanical rooms, public lobbies, restrooms, stairways, and storage rooms
- Spaces with only one luminaire with rated input power less than 100 W
- Space types with lighting power allowance of less than 0.6 W/sq ft.
Exceptions to C405.2.1.2 are:
- Areas that have only one luminaire, with rated power less than 100 W
- Areas that are controlled by an occupant-sensing device
- Corridors, equipment rooms, storerooms, restrooms, public lobbies, electrical rooms, or mechanical rooms
- Sleeping units
- Spaces that use less than 0.6 W/sq ft
- Daylighting spaces complying with C405.2.2.3.2.
Automatic lighting controls
In addition to manual controls, ASHRAE 90.1 and IECC require automatic controls for interior lighting. Automatic time control and occupancy based (occupancy sensors) are methods that can be used to comply. Requirements are defined in IECC Section C405.2.2 and ASHRAE 90.1 Section 9.4.1.
IECC mandates automatic time switch devices in addition to manual controls. This can be accomplished using lighting control systems (LCS), building automation systems (BAS), and/or digital time switches. When an automatic time switch control device is used, an override is to be located in a readily accessible space with a maximum override up to 2 hours. Overrides are to be zoned up to 5,000 sq ft. In malls, arcades, auditoriums, single tenant retail spaces, industrial facilities, and arenas, the override can exceed two hours with a captive key and can be zoned more than 20,000 sq ft.
This IECC mandate may not be the most efficient or practical method for most spaces such as private offices and classrooms. IECC allows engineers to design with occupancy sensors in lieu of time switch based devices and systems. Occupancy sensors per C405.2.2.2 are required in all classrooms, conference/meeting rooms, employee lunch and break rooms, private offices, restrooms, storage rooms, janitorial closets, and other spaces 300 sq ft or smaller enclosed by ceiling height partitions. Occupancy sensors for these spaces shall turn the lights off after 30 minutes of being unoccupied. In addition, the occupancy sensor must be manual-on or 50% auto-on/50% manual-on. (Manual-on occupancy sensors are also known as vacancy sensors.) Full automatic-on is acceptable in public corridors, stairways, restrooms, primary building entrance areas, lobbies, and where occupants would be endangered due to safety and security.
Exceptions to C405.2.2.1 and C405.2.2.2 for automatic time switches and occupancy sensors are in sleeping areas where patient care is directly provided, continuous operation/occupancy, or where automatic shut-off would endanger occupant safety and security (see Table 1).
ASHRAE 90.1 is very similar to the requirements of IECC with the following differences. Automatic schedule based controls shall be zoned up to 25,000 sq ft but for no more than one floor. A signal from an alarm/security system can override the lights to off during unoccupied hours. See Table 2 for the areas that require the lighting to turn off after 30 minutes of all occupants leaving a space.
Exceptions to these are spaces with multi-scene control systems, shop and laboratory classrooms, spaces that would endanger occupants’ safety and security, and lighting required for 24-hour operation.
ASHRAE 90.1 mandatory provision 9.4 outlines the requirements for lighting controls. A general statement in the first paragraph requires that any automatic control device for building interiors be either manual-on or controlled to automatically turn on to not more than 50%. Full automatic-on is only allowed public corridors and stairwells, restrooms, primary building entrance areas, and lobbies. In addition, full automatic-on is allowed where manual-on operation would endanger the safety and security of the occupants.
There are several ways to satisfy this mandate, one of which for a small room is to use a stand-alone vacancy sensor in lieu of an occupancy sensor. Vacancy sensors require manual-on by pressing or toggling a switch. If occupancy is not detected after a selected time period, the lights will turn off and must again be manually turned on. Wall-mounted vacancy sensors are almost identical to wall-mounted occupancy sensors. These devices use the same technology, with the exception of how the lights are turned on. Both of these devices can be manually turned off using the pushbutton switch.
For larger and more complex rooms such as school classrooms that also require daylighting zones, a lighting control system or BAS may be necessary. Using a wall-mounted or ceiling-mounted occupancy sensor and momentary switches (as vacancy switches) would be the minimum condition.
Daylight zone control
Per IECC, daylight zones are required and must have individual control (manual or automatic) of the lights independent of general area lighting and controlled per C405.2.2.3.1 (manual daylighting controls) or C405.2.2.3.2 (automatic daylighting controls). Each daylight control zone has to be ≤2500 sq ft. Contiguous daylight zones adjacent to vertical fenestrations can be controlled by a single controlling device if the zone doesn’t include areas facing more than two adjacent orientations (i.e., north, east, south, and west). Daylight zones under skylights >15 ft from the perimeter must be controlled separately from daylight zones adjacent to vertical fenestrations.
Exceptions to this rule are daylight spaces either enclosed by walls or ceiling height partitions or containing one or two light fixtures. General lighting would not have to have a separate switch.
Natural top lighting
When natural daylighting is used for top lighting (skylights, tubular daylighting devices, etc.), ASHRAE 90.1- 2010 Section 184.108.40.206 and IECC-2012 Section C402.3.2.1 require automatic daylighting controls. Both codes are very similar. The lighting in the daylit area must be separately controlled by at least one multilevel photocontrol and be remotely controlled and readily accessible. The artificial lighting must be continuously dimmable or step dimmed. Both require a minimum of one step no greater than 35%, and ASHRAE requires a second step between 50% and 70%. There are many fluorescent ballast and LED drivers that can provide either required continuous diming or stepped dimming. For the daylighting controls, the light fixtures can have integral light sensors or one light sensor for a zone (group) of light fixtures.
ASHRAE exceptions to 220.127.116.11 are:
- Daylighted areas under skylights where it is documented that existing adjacent structures or natural objects block direct beam sunlight for more than 1,500 daytime hours per year between 8 a.m. and 4 p.m.
- Daylighted areas where the skylight effective aperture (EA) is less than 0.6%
- Building Climate Zone 8 with daylight areas totaling less than 1,500 sq ft in an enclosed space.
IECC exceptions to C402.3.2.1 are:
- Buildings in Climate Zones 6 through 8
- Spaces where the designated general lighting power densities are less than 0.5 W/sq ft
- Areas where it is documented that existing structures or natural objects block direct beam sunlight on at least half of the roof over the enclosed area for more than 1,500 daytime hours per year between 8 a.m. and 4 p.m.
Spaces where the daylight zone under rooftop monitors is greater than 50% of the enclosed space floor area.