LED lighting and control system design considerations
- Review lighting control design requirements.
- Explore the IES Handbook and ASHRAE Standard 90.1.
- Evaluate the modeling methods for lighting design.
As much as the previous generation of electrical engineers and lighting designers may hate to admit, the days of multilamp T8 or T12 fluorescent fixtures—with 6- to 8-ft on-center spacings, accent wall sconces, multilamp chandeliers, and wiring line voltage switches—are no longer the norm.
The energy-conscious standards, such as ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, International Energy Conservation Code (IECC), and California’s Title 24, have made it more difficult to consider specifying incandescent, most fluorescent, and high-intensity discharge (HID) fixtures in modern designs. The LED revolution also brings smart, plug-and-play-style lighting devices and control systems that minimize installation and commission time, resulting in a cleaner and smarter product for the client.
The trade-off for this revolution is increased design times due to lighting-power density (LPD) restrictions per space, becoming more familiar with the various lighting control and networked systems offered by major manufacturers, and reviewing and designing to the applicable standards that many state and federal projects are now requiring.
It can be a delicate balancing act between meeting the required foot-candle levels, staying under the watts-per-square-foot LPD limits using an appropriate fixture, using the appropriate driver size, incorporating the required controls, and finally showing this in a clear and concise manner on construction drawings so a contractor can decipher what it is you’ve tried to design. It is also an educational effort for installation contractors to verify that the fixture has the correct driver installed, as the fixture from the outside looks the same. It is no longer two, three, or four lamps that are easy to distinguish.
Here are some general principles to follow when reviewing requirements for a new construction or renovation lighting design project:
- Most spaces now require more lighting controls than a simple on/off toggle switch. There are many control systems available that make design and installation easier.
- To meet the LPD limits of the new ASHRAE 90.1 edition, IECC, or California Title 24, you’ll most likely want to use LED fixtures instead of more energy-intensive lighting options.
- Overlighting a space can be as undesirable as underlighting a space. Aim to be within +/-10% of the target foot-candles typically found in the Illuminating Engineering Society (IES) Lighting Handbook.
- With so many options for LED lighting fixtures, even obscure architectural fixtures can be used and still meet codes.
- Minimize glare from intensive computer screen areas by looking at indirect and direct fixtures with shielding on the downlight side of the fixture.
- Clients appreciate rendered 3-D images of their new facilities showing the lighting within. With minimal effort, adding some small details and color can look impressive. Three-dimensional-rendered models are not an option for all consultants.
Standards driving design
Two main standards driving the design of lighting and lighting control systems are the IES Illuminating Handbook (2011) and ASHRAE 90.1, Chapters 8 and 9 (2007, 2010, 2013, 2016). For military projects, the Unified Facilities Criteria (UFC) documents, such as UFC 3-530-01: Interior and exterior lighting systems and controls, with Change 3, also show requirements for what is expected in facilities. Various state, city, campus or client-provided standards also must be considered.
The 2011 version of the IES Handbook provides recommended foot-candle levels for various indoor and outdoor spaces. It’s a great source for everything from a dormitory bedroom to an outdoor mechanical yard at a manufacturing plant. Unless the client has their own required foot-candle levels spelled out, they typically reference this as a source for lighting levels.
ASHRAE 90.1, Chapters 6, 8, and 9, were developed to drastically reduce overall building energy usage by imposing strict controls to HVAC, lighting, and power.
For lighting, ASHRAE 90.1 provides required LPD limits and control schemes for several common space types. Note that ASHRAE 90.1 has four versions listed above because state adoption of the standard varies and may reference one of those versions that are referenced. Each version becomes more strict, lowering LPD limits on spaces and increasing control requirements all in the name of energy savings.
If a building is pursuing LEED certification, the energy-model credit specifies a percentage lower than what is allowed in ASHRAE 90.1. To help cut building-wide energy usage, lighting designers can attempt to limit their LPD as much as possible by using more efficient fixtures to contribute to overall energy savings. As the LEED certification level goes up, so does the energy savings required in the building-wide energy model. For example, when ASHRAE 90.1-2007 applies, one could comfortably use typical multilamp 28-W fluorescent tube fixtures, line voltage switching, and other basic controls and still meet code. The 2010 version introduced automatic receptacle controls, drastically cut down the LPD limits, added occupancy- and daylight-sensor requirements, and added bilevel switching requirements, effectively expelling line voltage systems. These added control measures force the designer to completely reimagine how to control lighting.
Lighting control design requirements
The following is an overview of the basic lighting control requirements and devices to consider during design and is by no means an exhaustive code review. There are many exceptions to certain control requirements including 24-hour operation and security or safety concerns, among others. Exceptions should be cleared with the client prior to removing them from the design. Reference Chapters 6, 8, and 9 of ASHRAE 90.1 for more information, exceptions, and sequences of operation for specific space types. The control requirements and devices are:
- Occupancy sensors are mounted in the ceiling or on a wall switch, available in passive infrared (PIR) or “dual-technology,” which incorporates PIR plus either a microphonics or ultrasonic sensor. PIR is limited to line-of-sight movement only, so it is not a good choice in areas with lots of obstructions like tall cubicle walls, large equipment, or restroom stall doors. Microphonics uses a tiny microphone to detect sound, while ultrasonic sensors emit high-frequency sound waves to detect motion. The sensors operate by turning on the lights in the space upon occupancy to a level determined in ASHRAE 90.1 and turning them off automatically after 20 to 30 minutes when unoccupied. Most space types in a commercial application, aside from mechanical/electrical rooms, require occupancy sensors.
- Daylight sensors are mounted in the ceiling, ideally with lights between the sensor and a window. They operate by taking a reading of total available light in the space. Throughout the day, sensors dim the artificial lights to where the artificial light level plus the sunlight level in the space meets the programmed foot-candle either at the work surface (generally 30 in. above the floor) or on the floor, depending on space usage. Per the 2016 version of ASHRAE 90.1, any space with windows or skylights and total lighting wattage in the sunlit area greater or equal than 150 W requires daylight-sensor control.
- Automatic receptacle control was introduced in ASHRAE 90.1-2010 and consists of a relay pack that controls 50% of the electrical receptacles in the space. Let’s consider two different ways how a private office with four duplex receptacles is controlled:
- Two full duplex receptacles will be controlled.
- The bottom (or top) receptacle on each of four duplex receptacles is controlled.
- Controlled receptacles shall be marked with the International Power Symbol per NFPA 70: National Electric Code (NEC), Article 406.3 (E). The receptacles can be tied to the operation of the occupancy sensor in the space or they can be incorporated into a scheduled time-of-day shutdown. In the case of occupancy sensor-controlled receptacles, they turn on upon occupancy and turn off after 20 to 30 minutes of being unoccupied. These receptacles are a good choice to plug in noncritical loads, such as a desk lamp that may inadvertently be left on. (per ASHRAE 90.1-2016). A best practice is to bring this up early in the design process so clients are not blindsided.
- Bilevel lighting control is a method of having at least two separate lighting-output levels for a space, one of which may be automatic upon entry while the second is manual. A smart switch with full dimming capabilities also meets this requirement, provided the automatic operation is no higher than 50%. When an occupant enters the space, the lights come on to 50% output automatically. If the occupant wants full light output, they manually hit the second-level button (or dimmer buttons) on the wall switch. This requirement is in place to prevent wasted energy on someone stopping in briefly and leaving immediately. For example, a janitor closet, where the janitor would open the door, grab a broom and leave, triggering the occupancy sensor. This requirement can be programmed into the system or be a pre-installed option on a relay pack.
- Automatic HVAC shutdown is another requirement of ASHRAE 90.1 in Chapter 6. Typically provided on a building management system (BMS) time-of-day schedule, another option is to integrate HVAC operation in spaces with lighting control occupancy sensors. Many lighting control systems offer options for this integration. If the lighting control system sensor is used, the lighting controls notify the HVAC/BMS to turn on in the space. When the occupancy sensor times out after 20 to 30 minutes, the signal is sent to the HVAC/BMS to turn off or lower HVAC to the space, saving energy from running HVAC in an empty room for extended periods. There are various interface protocol options, and the choice will depend on how the mechanical BMS is set up. A simple contact closure hard-wired to the BMS can be used from a per-room relay basis, or the preferred method is to use a BACnet (or other) interface module that resides on the lighting control system network that converts the signal to the correct protocol for the particular BMS. Then logic is used for input into the spaces for HVAC control. Always confer with your mechanical engineer on the project to confirm his or her preferred protocol. This strategy is typically used in most occupied spaces like offices, conference rooms, control rooms, and break rooms.
Once most states upgraded from the ASHRAE 90.1-2007 energy standard to the 2010 edition, the lighting industry produced more intelligent lighting control systems that met the new standard. Several manufacturers offer a base control system with 0 to 10 V-enabled dimming drivers for the fixtures and daisy-chained Power over Ethernet (PoE) Category-5e (CAT-5e)-enabled control devices including occupancy sensors, daylight sensors, and wall switches; all controlled by a small dimming relay pack mounted above the ceiling. These connected devices can all operate with minimal or no preprogramming.
Various so-called smart-switch options replace 3- and 4-way line voltage switching, as multiple zones can be controlled within the same switch instead of having to wire multiple line voltage switches. These switches can include occupancy sensors, dimming buttons, and programmable scene buttons or they can even be a small graphic touch screen, which allows multiple scenes with added control options available. The smart switches are typically powered from the room controller through the category cabling, with devices containing 2-RJ45 ports. The touch-screen option may require an additional small power supply, depending on the manufacturer.
With these system devices, we can easily incorporate HVAC and automatic receptacle control all within the same system. Need emergency lighting fixtures via an NFPA 110: Standard for Emergency and Standby Power Systems generator or UL 924: Standard for Emergency Lighting and Power Equipment–listed lighting inverter system? There’s an emergency relay pack for that, too. Each space can operate alone on its own network or be tied together with several rooms. With just a few additional networking devices available from the lighting control manufacturer, the entire building’s lighting control can be connected on a single network and feed back to a central control computer. Depending on the system options chosen, even a smartphone with protected credentials can control each individual light in an entire building.
Some manufacturers are replacing 0 to 10 V dimming cables with CAT-5e or CAT-6 cables and powering the lights and dimming with the same CAT cable. The possibilities are virtually unlimited and can be client-driven, resulting in a totally customizable system that meets client needs. Since most installations will not require overly complicated controls, these plug-and-play-style systems minimize contractor wiring and commission time.
Figure 1, for example, shows a schematic of how a private office could be interconnected to all the smart devices with CAT-5e cable and using 0 to 10 V dimming controls.
Lighting–power density and foot–candles
LPD, watts per square foot limits are provided by ASHRAE 90.1 and provide a framework of how many watts per square foot a fixture can use to light a space of a certain size and type. The LPD ranges vary from very low for a janitor closet or storage room to much higher for a classroom or workshop. The limits are generally met easily with LED fixtures.
Although ASHRAE 90.1 offers limits on specific space types, compliance operates on the entire building. The designer has the option to use the building method, a single LPD for the whole building based on the type of building, or the space-by-space method using different LPD limits for each space type to calculate the total LPD.
The designer can use the ASHRAE 90.1 Interactive Compliance Form to incorporate the LPD limits to a total of allowed lighting watts for the building. Despite which method is used, if the entire building’s actual lighting LPD level is lower than the allowed LPD, the designer is compliant. If using the space-by-space method, there’s no reason to worry if one or two rooms are slightly over the limit. It is common to be 25% to 40% or more under the allowed watts for a large project with many different space types. This percentage savings below ASHRAE 90.1 becomes much more important when designing for LEED projects, as previously discussed.
Foot-candles are a measure of illuminance at a chosen horizontal plane in a space. Three main calculation plane heights we see are at the floor surface for corridors and lobbies, at 30 in. for the desk level in office space, and 42 in. for mechanical space. Many different calculation planes are required for different space types and are described in the IES Handbook.
Choosing the right lighting fixture
There are many types of lighting fixtures and options to choose from to meet the needs of a space. Consider these factors when choosing fixtures:
Communication: It’s important to communicate with the mechanical engineer regarding the design temperature of an industrial space, especially at the ceiling, as heat rises. Some industrial fixtures have different temperature ratings based on the distance they’re suspended from the ceiling. It’s also important to consider how the space will be used to avoid any possible damage to the fixtures.
Also consider wire guard covers for the industrial areas and vandal-resistant lens covers or housings for the more public options. Typically, an industrial-style or outdoor fixture will have these options available as an add-on.
Location type: If the space is considered a hazardous location, it may be necessary to have an appropriately sealed and UL-listed fixture for the classification of these types of spaces. Many manufacturers offer these rated fixtures, but they may be more expensive.
Ceiling type: Is it a drop-in acoustic tile ceiling or gypsum board? The fixture you choose should be not only appropriate for the space but should minimize installation costs for a contractor. Installing recessed fixtures in gypsum board ceilings can increase construction costs considerably for a larger project. Try to choose a surface-mounted or suspended fixture if you have gypsum board ceilings and the space doesn’t need recessed fixtures. An exception to this rule might be in restrooms, where you want a clean design. Recessed linear strip fixtures are a good idea in restrooms for this reason.
Consider the LED Kelvin temperature rating (K-temp): This is a measure of the light’s color output, from a warmer orange to cooler blue with daylight at the end of the spectrum. Some examples of temperatures in lighting design are warmer high-pressure sodium fixtures (typically 2000 to 2200 K), typical office setting (3500 to 5000 K), and a cooler blue/white 6000+ K. Most LED fixtures have several K-Temp packages for the same fixture.
Avoid mixing K-Temps and color rendering index (CRI) ratings, since both can cause different effects regarding how items appear in color in a building unless the application calls for it. It can be disorienting to walk from a 4000-K office into a hallway that’s 2700 K and then into the kitchen where it’s 5500 K. If the project is a partial renovation, consider matching the K-Temp to what is already installed to be consistent.
Because of all the current lighting options, it’s more difficult to consider a contractor’s substitutions or other lighting options from another manufacturer. Previously, a two-lamp fluorescent was standard regardless of the manufacturer. Now it becomes more essential to list minimum lumen output and maximum wattage input in a fixture schedule. With strict LPD limits, it is imperative for manufacturer representatives providing substitutions to use due diligence and light modeling software to prove their proposed fixtures meet or outperform the basis-of-design fixtures.
Three-dimensional modeling design
Three-dimensional modeling of the building and spaces is crucial to confirming a design is accurate and code-compliant.
There are a lot of options for light modeling software. Most major manufacturers have photometric files for each of their fixtures, which can be downloaded and imported into your chosen software. These files represent how a fixture looks and performs in a real-world installation.
The key to making a great 3-D design is adding in representations of actual objects in the space:
- Large equipment like tanks, generators, switchgear, pumps
- Equipment racks in communications rooms
- Lockers and large shelving
- Restroom stall doors and shower curtains.
This is important because, while the design of an empty room may meet code, there could be dark areas once the space is populated with actual equipment and obstructions. Maybe the initial design failed to account for where the rows of motor control center sections were going to be placed, and now lights are installed directly above the equipment, rendering the design ineffective for the light placements. These problem areas are avoided by modeling planned obstructions if budget allows (Figure 2).
Consider the fixture light-loss factor (LLF) when modeling. All lighting fixtures have a drop-off of applicable light output over time due to dirty lenses, reflectors, ballast or LED driver depreciation, and actual lamp-source failure. LED drivers and lamps tend to have better performance toward their end of life than their predecessors. For a long time, a recommended LLF was 0.7 (70% of rated light output), but this was based around less-efficient fixtures and lamp/ballast sources with shorter life spans. When we model lighting designs, we want to model for the worst-case scenario. The worst case for light fixtures is at their end of life. The designer can adjust the LLF of the fixtures in modeling software so the output is reduced.
By adding color and predesigned objects to specific areas of the modeled environment, the model can impress clients with actual reflectivity values. Adding something as minimal as green grass color to an outdoor lighting project can make a big, gray, blocky model more realistic. For example, add yellow-colored generators, safety-yellow equipment pads, school-colored lockers, desks in a classroom, a wood floor on a basketball court, or people standing around to show scale. These make a difference and clients appreciate the presentation.
Approaches to control systems and construction drawings
The easiest way to convey how a lighting system is designed to a contractor or a cost estimator is to standardize how to show these systems.
As different clients and projects require different levels of detail, there are a couple methods that seem to work well.
One approach is to provide a table with different sequences of operations (SO) and assigning room numbers to the proper SO section. For the plans, only show the lights, smart switch locations, and occupancy/daylight-sensor locations. This approach holds the contractor responsible for providing the appropriate relays and networking devices to achieve the assigned SO per room based on the selected template.
A challenge with this approach is that it makes it difficult to provide an accurate cost estimate. If specifications aren’t tight enough, this may invoke several information requests from the contractor, or a change order. As a result, the engineer may be forced to count all the devices, prolonging the process, which also adds to the budget.
Another approach uses the same plan-drawing approach, showing only the major devices per room. However, this design is based on an actual lighting control system available from a major manufacturer. All the devices necessary for the design could be accounted for in a table broken down by room on one axis and by device on the other axis. Provide modified typical wiring-schematic template plans in details for the various rooms in the project and assign the applicable room numbers to each schematic. Reference Figure 1 for an example.
These schematic plans show an example room and its associated SO with the required relays, cabling types, and connections to the control devices and appropriate switches. This information is helpful for cost estimators and contractors to visualize the parts and labor that will be required for the project. Depending on the client, the designer can provide part numbers of the basis-of-design manufacturers or provide function name only (for example, dimming relay, wall switch with PIR, etc.). To avoid sole-sourced products, provide acceptable product options from different manufacturers that would be considered equal in performance and include notes allowing substitutions with prior approval to bid, providing the alternative system meets the SO for the spaces shown.
Designers want to avoid mistakes and try to think of everything that could go wrong, but it’s hard to learn without experiencing the process a few times.
For example, a common design approach in restrooms is to put wall-wash lights in the ceiling along the walls above sinks and toilets. In a recent project, 4-in.-wide LED strip fixtures were recessed in the acoustic tile ceiling along the walls. The owner was not happy with the lighting in the restroom because he could see the wobbly, uneven tile work on the walls. The solution was to move the lights away from the walls to the next T-bar. In this case, it wasn’t technically the lighting that was the problem, but the tile contractor’s work. It’s something to consider if there is intricate tile work in restrooms or on other walls.
LED lighting and control systems are evolving and becoming smarter each year. Designers need to stay current on lighting design options and methods while being code-compliant. Codes are becoming more stringent and software design is offering more options for deliverables. Coordinating with mechanical engineers is important because the systems can now be interconnected. Tighten up fixture schedules and specifications to avoid headaches entertaining substitutions. This all costs designers time, but the product is a long-lasting system that can look great and make clients happy.