Commercial lighting, controls and energy codes

Lighting is the most visible part of a commercial electrical installation and, together with its controls, one of the largest. In two decades it has changed almost completely: fluorescent and high-intensity discharge lamps with magnetic ballasts have given way to LED luminaires with electronic drivers, and simple wall switches to occupancy sensors, daylight controls and networked lighting systems mandated by energy codes. This lesson covers lighting branch circuits and voltages, LED drivers and their electrical behavior, dimming and control protocols, the energy code requirements for lighting power and controls, outdoor and sign lighting, and the practical work of installing, commissioning and troubleshooting modern lighting systems. Emergency lighting was covered in Lesson 9.

Lighting circuits and voltages

In US commercial buildings, general lighting is usually supplied at 277 V, line to neutral from a 480Y/277 V system, which reduces current and voltage drop compared with 120 V. 210.6 limits branch circuit voltages for luminaires (for example, 277 V lighting is permitted in commercial and industrial occupancies under specified mounting conditions, and dwelling units are limited to 120 V for luminaires). Article 410 covers luminaires, including wiring, support, recessed luminaires and clearance to insulation, and luminaires in damp and wet locations.

Lighting loads in offices, stores and warehouses are continuous (Lesson 1), so branch circuits are loaded to no more than 80% of the overcurrent device rating. Multiwire branch circuits sharing a neutral are common for lighting and need a means to disconnect all ungrounded conductors simultaneously (handle-tied or multipole breakers), and the shared neutral must be sized for harmonic currents from electronic drivers (Lesson 1 discussed neutral sizing).

LED luminaires and drivers

An LED luminaire contains LED arrays, which need a regulated DC current, and a driver, an electronic power supply that converts the AC supply to that current. The driver, not the LEDs, determines most of the luminaire's electrical behavior:

• Inrush current: when switched on, the driver's input capacitors charge, drawing a very brief current spike that can be tens of amperes per driver for a fraction of a millisecond. Many drivers switched together on one circuit can trip breakers or weld relay and switch contacts, so manufacturers specify the maximum number of drivers per breaker and controls are rated for LED inrush.
• Power factor and harmonics: good drivers have a power factor above 0.9 and total harmonic distortion of input current below about 20%; cheap drivers can be much worse, increasing neutral current and transformer heating.
• Operating voltage range: many commercial drivers accept 120 to 277 V; others are designed for 347 V or 480 V, and the voltage on the label must match the circuit.
• Lifetime: LED luminaires are rated by L70 (hours until light output falls to 70% of initial), often 50,000 to 100,000 hours; drivers, especially their electrolytic capacitors, often fail first, particularly in hot locations.

Dimming and control protocols

Most commercial LED drivers are dimmable, controlled by one of several methods:

Control wiring must be installed according to its classification. Class 2 0-10 V wiring may need separation from line-voltage conductors in the same luminaire or box unless the cable and devices are suitably rated, which manufacturers address with barriers or Class 1 rated control conductors. The polarity of 0-10 V wiring (violet and gray wires by common convention) must be correct, and long control runs may need shielded cable to avoid flicker from induced noise.

Lighting controls required by energy codes

Energy codes require controls that turn lights off or down when they are not needed. Typical requirements in current codes include:

• Automatic shutoff: occupancy or vacancy sensors in offices, classrooms, conference rooms, washrooms and storage rooms, or time scheduling elsewhere, so that lights turn off when spaces are empty.
• Partial-off or reduced levels: in warehouses, corridors, stairwells and parking garages, sensors reduce light output by at least about 50% when unoccupied.
• Daylight responsive controls: in areas near windows and skylights (daylight zones), photosensors dim the lights in response to available daylight.
• Local control and multilevel dimming in most spaces, so occupants can reduce light when full output is not needed.
• Exterior lighting controls: automatic shutoff during daylight and reduction late at night.
• Receptacle control in some codes: a portion of receptacles in offices automatically switched off when spaces are unoccupied, with marking.

In the US, the International Energy Conservation Code (IECC) or ASHRAE 90.1, as adopted by each state or city, sets lighting power limits and control requirements; California has its own Title 24, Part 6, with extensive control and acceptance testing requirements. Acceptance testing of lighting controls by certified technicians is required in some jurisdictions.

Lighting power density

Energy codes also limit the installed lighting power, expressed as lighting power density (LPD) in W/m² (or W/ft²) for the building type or for each space type. Modern LED designs typically achieve 4 to 8 W/m² in offices, well below the code limits.

Installing and commissioning lighting controls

Many lighting complaints come from controls that were installed but not commissioned: sensors with default settings that turn lights off on people sitting quietly at desks, daylight sensors that dim too much or flicker, and schedules that do not match the building's hours. Good practice:

• Choose the right sensor technology: passive infrared (PIR) needs line of sight and detects movement; ultrasonic and microwave sensors detect smaller movements and see around obstacles but can be triggered by air movement; dual-technology sensors combine them.
• Place sensors according to manufacturer coverage patterns, away from HVAC diffusers and doorways where people walk past.
• Set time delays appropriately, often 15 to 20 minutes in offices, shorter in washrooms and storage, within the maximum allowed by the energy code.
• Calibrate daylight sensors with the space furnished and at representative times, setting the target light level and dimming limits.
• Program schedules, overrides and integration with the building automation system, and train the owner's staff.
• Document settings and provide control drawings, because networked systems with hundreds of devices are difficult to troubleshoot without records.

Outdoor and site lighting

Parking lot and site lighting brings its own issues: long circuits with significant voltage drop, poles that must be bonded and installed on engineered bases, hand holes and junction boxes exposed to water, and luminaires exposed to lightning and surges (surge protective devices in the driver or at the pole are common). Pole wiring needs fusing at each pole in many designs, and pole hand holes must be bonded and covered. Lighting near property lines and sky must comply with local bylaws on light trespass and glare, often using full-cutoff luminaires and lower color temperatures (3,000 K or less) to reduce sky glow and effects on wildlife, as dark-sky guidelines recommend.

Signs and outline lighting

Electric signs and outline lighting have specific rules: each sign must have a disconnecting means within sight of the sign or lockable, signs and their power supplies must be certified, branch circuits supplying signs in commercial buildings with entrances accessible to pedestrians are often required by the code to be provided at each entrance, and LED sign power supplies and their secondary wiring have their own installation rules.

NEC Article 600 covers electric signs and outline lighting, including the required sign outlet at each entrance of commercial occupancies (600.5), the disconnecting means within sight of the sign or lockable (600.6), and Class 2 LED sign illumination systems.