Lighting and lighting controls

Lighting is the most visible part of the electrical system and one of the most closely regulated for energy. In two decades the industry has moved almost entirely from fluorescent and incandescent sources to light-emitting diodes (LEDs), and from simple wall switches to networked controls that dim lights by daylight and occupancy and report energy use. Lighting also has life safety roles: emergency lighting and exit signs guide people out when the power fails.

For the constructor, lighting brings large quantities of fixtures with long submittal lists, tight ceiling coordination with ducts, sprinklers and diffusers, controls programming and commissioning, and inspections of emergency lighting. Substitutions are common and need care, because a cheaper fixture can change light levels, glare, energy compliance and controls compatibility.

Light, lumens and illuminance

Lighting has its own vocabulary. Luminous flux, measured in lumens (lm), is the total light a source emits. Efficacy, in lumens per watt, measures how efficiently it does so; modern LED fixtures commonly exceed 100 lm/W, roughly double the efficacy of the fluorescent fixtures they replaced. Illuminance is the light falling on a surface.

US practice measures illuminance in footcandles (lumens per square foot), with lux used in some specifications (1 footcandle = 10.76 lux).

Recommended light levels come from the Illuminating Engineering Society (IES) and depend on the task: around 300 to 500 lux (30 to 50 footcandles) for general office work, less for corridors, more for detailed tasks. Quality matters as much as quantity: glare, uniformity, color rendering (CRI or TM-30 metrics), color temperature (warm 2,700 to 3,000 K, neutral 3,500 to 4,000 K) and flicker all affect comfort and productivity.

Estimating fixture quantities: the lumen method

Designers use lighting software for layouts, but the lumen method gives a quick estimate of how many fixtures a room needs. It accounts for how much of each fixture's light reaches the work plane (the coefficient of utilization, CU) and how light output falls with age and dirt (the light loss factor, LLF).

Lighting power density and energy codes

Energy codes limit the electrical power that lighting may use, expressed as lighting power density (LPD): installed lighting watts divided by floor area. Codes allow either a whole-building allowance or a space-by-space allowance. LED technology has driven allowances down sharply over the past decade.

ASHRAE 90.1-2022 and the IECC 2024 set interior lighting power allowances by building area or space type and require automatic shutoff, occupancy-based controls and daylight responsive controls in many spaces.

Substituting a fixture with lower efficacy, for example a decorative fixture at 60 lm/W instead of 120 lm/W, can double the installed watts for the same light and break compliance. Energy code compliance forms are part of the permit and are often checked again at substantial completion.

Lighting controls

Controls cut lighting energy by turning lights off or down when they are not needed. Common strategies are:

• Occupancy sensors, which turn lights on when people enter and off when the space is empty, and vacancy sensors, which require manual on but turn lights off automatically.
• Daylight harvesting, which dims fixtures near windows and skylights when daylight is sufficient, using photosensors.
• Time scheduling, which turns lights off after hours with override switches.
• Task tuning or high-end trim, which sets maximum output below 100 percent where full output is not needed.
• Networked lighting controls, in which each fixture or zone communicates over wired or wireless networks, allowing reprogramming, energy reporting and integration with the BAS.

Daylight zones are defined by the geometry of windows and skylights. A common rule in energy codes is that the primary sidelit zone extends from the window wall a distance equal to the window head height, so a window head at 2.7 meters (9 ft) creates a daylight zone about 2.7 meters deep along the façade.

Controls are a frequent commissioning problem: sensors placed where they cannot see occupants, photosensors calibrated wrongly so lights stay dim on cloudy days, or time-outs set so short that lights switch off on people at desks. Functional testing of a sample of each control type, with documented settings, is part of good practice and is required by many energy codes.

Fixtures, drivers and dimming

LED fixtures contain the LED modules and a driver, an electronic power supply that converts line voltage to the low-voltage direct current the LEDs need and provides dimming. Common dimming methods are 0–10 V analog control, digital protocols such as DALI, and phase dimming for some small fixtures. Driver and control compatibility must be checked at submittal, because mismatches cause flicker, poor dimming range or failure. LED fixtures also create harmonic currents and high inrush current at switch-on, which affects breaker selection and the number of fixtures on a circuit.

Emergency lighting and exit signs

Emergency lighting illuminates exit routes when normal power fails, from batteries in unit equipment or fixtures, from a central battery system or from the emergency generator. Exit signs mark the way out.

In the United States, the IBC (Section 1008) and NFPA 101 require emergency lighting along the means of egress with an initial average of at least 1 footcandle (about 11 lux) and a minimum of 0.1 footcandle at floor level, for at least 90 minutes. Exit signs may be red or green depending on local rules and must be listed to UL 924.

Emergency lighting is tested at completion by simulating a power failure for the full duration and checking light levels along exit routes, often at night with a light meter. Monthly and annual tests follow in service. Construction managers should plan these tests early, because failures found late can require additional fixtures or heads.

Exterior and site lighting

Parking lots, walkways and building façades need lighting for safety and security, but codes and municipalities increasingly limit light trespass and sky glow. Dark-sky principles, such as full cut-off fixtures, warm color temperatures and curfew dimming, are written into many municipal by-laws and green building programs. Site lighting also involves poles, bases, underground conduit and coordination with civil work and landscaping.

Lighting quality: color, glare and flicker

Quantity of light is only part of the story. Color rendering index (CRI) measures how faithfully a light source shows colors compared with a reference source; 80 is common for offices and 90 or higher for retail, healthcare and galleries. Correlated color temperature (CCT), in kelvins, describes whether light looks warm (2,700 to 3,000 K) or cool (4,000 to 5,000 K), and projects usually standardize one or two values so that fixtures from different makers match. Mixing color temperatures in a single space is a common and visible installation error.

Glare comes from bright sources in the field of view and is controlled with fixture optics, shielding and placement; the unified glare rating (UGR) is often specified for offices. Flicker, rapid fluctuation of light output that can cause headaches even when it is not noticed, depends on the LED driver and dimming method. Specifications increasingly limit flicker, and substitutions that change drivers should be reviewed for it.

Submittals, substitutions and mock-ups

Lighting is one of the most substituted trades, because fixtures from different makers can look similar on paper. A substitution must match light output, distribution, efficacy, CRI, CCT, dimming compatibility, emergency options, finish and warranty, and it must still meet the lighting power density the energy compliance was based on. For important spaces, a mock-up of a few fixtures on site, viewed with the owner and designer, settles questions about appearance and glare before hundreds of fixtures are ordered.