Lighting system design
- Analyze eight key factors that must be considered when specifying lighting systems.
- Recall that codes, standards, siting, controls, and many other factors must be taken into account in each design.
- Create a lighting design that meets the owner’s needs and adheres to required code.
Designing lighting for a building may seem simple at first, but there are several items a lighting designer must consider. Where should someone new to lighting design start? The eight key factors in lighting design include:
- The owner’s project requirements (OPR) that include project costs and schedule
- The basis of design (BOD)
- Codes and standards, including energy guidelines
- Sustainability certifications (U.S. Green Building Council’s LEED, Energy Star, etc.)
- Recommended lighting levels
- Lifecycle costs
- Safety and security
- Maintenance and warranty.
Factor 1: OPR
The first step in a successful lighting design is to obtain the OPR. This is a document prepared by the owner of the building. This can also be the tenant if the space being designed is a tenant space that is rented. The OPR explains how the owner would like the space to be used and operated. The OPR should include:
- The goal for the design of the project
- How the building/space will be used
- The budget cost of the project (construction and soft costs)
- The schedule for construction completion
- Energy efficiency goals (e.g., Energy Star)
- Standards and codes including energy codes
- Sustainability goals
- Types of materials to be used
- Return on investment (ROI) and lifecycle costs requirements
- Safety and security requirements
- Training requirements
- Warranty requirements.
Most projects do not incorporate an OPR. This can lead to an owner receiving a building/tenant space after construction is completed that does not meet what the owner had envisioned. This can lead to costly redesigns, increased costs, and construction delays. An OPR that is provided prior to design is critical to the success of a project.
The majority of projects have an OPR only when the project is pursuing LEED certification. LEED’s Fundamental Commissioning prerequisite requires that an OPR be completed. The commissioning authority (CxA) is required to have the OPR so that the commissioning team can validate that what is being designed and built meets the owner’s vision through the OPR.
The OPR is essential to a successful project, yet few projects use this important document. In fact, some LEED projects develop the OPR after the design has already started. In many of these cases, the energy consultant or CxA is contracted and brought onto the team after the design has already started.
The CxA’s role is to represent the owner. Many times the CxA’s contract lies with the architectural and/or engineering firm, and occasionally with the contractor. Regardless of with whom the contract lies, the CxA needs to ensure that the design does not begin until the OPR is completed.
Here is a sample preliminary OPR’s lighting goals for the lighting system for a commercial office building:
- Lighting design including energy efficiency and controls shall conform to ASHRAE Standard 90.1-2010.
- Maximize daylighting to all employees. Use daylighting controls and light switches for all private offices.
- Use LED lighting.
- Meet or exceed the recommended lighting levels in the Illuminating Engineering Society (IES) Lighting Handbook based upon people 25 to 65 yr old.
- Use 3,500 K color temperature for all lighting.
- Minimum of 80 color rendering index (CRI) for all lamps and light sources.
- Provide night lighting at all entrance doors to the building.
- Project is targeting LEED-NC v3 Silver certification at a minimum.
Factor 2: BOD
The BOD is a document developed by the architectural and engineering firms and before the schematic design phase. It is based on the OPR and describes the technical approach planned to meet the OPR. The BOD contains the design parameters to be used and identifies the parties involved. It lists who is responsible for each component of the design. For example, the BOD may state the lighting designer is responsible for the coordination and design of the lighting system.
LEED also requires the BOD as part of the Fundamental Commissioning prerequisite. This allows the CxA to determine how the design team plans to meet the OPR.The BOD should list applicable codes and standards if they are not found in the OPR. For example, an OPR may state, "provide an energy-efficient building." The BOD may state the design intent is to exceed ASHRAE Standard 90.1-2013 by 10%. It also should describe how the design intent will be met. A BOD for the above example may state the design will use high-performance lighting such as LEDs with efficacies with daylighting controls and occupancy/vacancy sensors.
Factor 3: Codes and standards
The sample OPR described earlier states that lighting controls are to be installed for all private offices. The OPR calls for light switches to be used for private offices. It does not state what type of control to use for non-offices. Some various types of controls are: on/off light switches, bi-level switches, dimmers, occupancy/vacancy sensors, and a time-of-day lighting controller.
The lighting designer will need to have the owner expand upon this preliminary OPR by asking specific questions such as: What type of lighting controls are desired? The lighting designer also needs to take into account the codes and sustainability goals such as LEED certification and/or Energy Star goals.
In our example, the owner is requiring that light switches instead of occupancy sensors be installed in private offices. But an energy code required for the project such as ASHRAE 90.1-2013 may require that occupancy sensors be installed in private offices. It is still possible to incorporate a light switch to control the lighting, but energy codes may dictate that an occupancy or vacancy sensor be used in conjunction with a light switch.
For example, a conference room may be required to switch the artificial lighting off when it is unoccupied due to an energy code. However, there may be a presentation in the room requiring some or all the lighting fixtures in the room to be turned off. An occupancy sensor can incorporate a switch to manually turn off the lighting. Figure 1 shows an occupancy sensor that has two manual on/off switches to control two separate loads; for example, one load can be the row of lighting fixtures closest to the presentation screen (if it is circuited in this manner). This switch can be changed to the off position by manually pushing the button for this load. The second switch could then control the rest of the room’s lighting fixtures.
The U.S. Dept. of Energy’s Building Energy Codes Program is a great resource to determine the energy code for a project. The lighting designer needs to ensure that the entire design team is using the same energy code. Many states allow either ASHRAE Standard 90.1 or the International Energy Conservation Code (IECC) to be used as the energy code for a project.
A clear BOD can help prevent the design of the lighting system meeting one energy code and the rest of the design team using another energy code as their basis of design. For example, a lighting designer may base the lighting system design on ASHRAE 90.1-2013 and complete the necessary Dept. of Energy COMcheck lighting compliance forms. The lighting designer then finds out, usually at the permitting stage, that the rest of the design team is using another energy code such as the 2015 edition of IECC. It is important that the OPR or BOD clarify the energy code to be used for design to avoid rework and project delays.
It is critical once the energy code has been identified that the lighting designer reviews and incorporates all the requirements of the code including lighting power density (Watts per square foot) and controls for the project. This will allow the designer to determine if the OPR can be met.
The lighting designer should inform the owner that occupancy sensors are required by the energy code for the project’s private offices. However, the lighting designer should try to determine why the owner had issues with occupancy sensors on a past project to avoid having similar issues with the new project. For example, the owner may have had a previous undesirable project that had occupancy sensors that turned lights off in a private office when the occupant was still in the room. The owner may resist having a design use occupancy sensors based upon this past undesirable experience.
PIR technology is a line-of-sight beam that reacts to heat motion across the sensor’s field of view. Figure 2 depicts a typical wall-occupancy PIR sensor’s coverage pattern. PIR technology works best in small enclosed rooms with a high level of occupant movement. A room occupant seated and typing at a desk is an example of minor motion. An example of a major motion is a person walking in and out of a room/space. Another example of major motion is sitting or standing with constant gestures or movements.A common issue with an occupancy sensor is locating a passive infrared (PIR) sensor too far away from the area where there is minor motion by the occupants. Another common issue is installing an occupancy sensor in a private office that has its coverage extending out to a corridor with the office door open. This can lead to the lighting fixtures in the office inadvertently turning on when building occupants walk past the office door but do not enter the office.
Figure 3 shows a floor plan of a typical office with a combination-wall PIR occupancy sensor and wall light switch. This layout depicts what the owner in our article had installed in his office building with the occupancy sensor issues.
The ideal location for the PIR occupancy sensor is shown in Figure 4. This layout allows the wall-mounted sensor to detect an occupant walking into the room (major movements) and is also close enough to the occupant’s main desk to detect the small minor movements. This layout in Figure 4 should have better results than the wall-mounted sensor located next to the door with the task area outside of the minor movement zone (Figure 3).
Figure 5 shows a typical wall-occupancy ultrasonic sensor’s coverage pattern. Another improvement would be to use an occupancy/vacancy sensor with dual technology including PIR and ultrasonic with self-adaptive technology. Ultrasonic technology senses when an occupant is in the room/space by bouncing ultrasonic waves off of objects (such as walls) and detecting a frequency shift in the transmitted and reflected waves. Ultrasonic sensors are good at detecting minor motions.
Dual-technology occupancy sensors using both PIR and ultrasonic technologies require that both technologies detect an occupant in a room/area to turn the lighting on. And only one of the technologies is needed to continually sense an occupant to keep the lighting on. The layout in Figure 6 is a typical dual-technology wall-occupancy sensor’s coverage areas.
Self-adaptive technology is where the sensor analyzes occupancy patterns and automatically tunes the sensor to have the greatest accuracy.
Other considerations for occupancy sensors include:
- PIR sensors should not be located within 4 ft of air vents.
- Ultrasonic sensors should be located at least 6 ft away from air vents.
- The door should be in clear view of an occupancy sensor, and the door (when open) cannot block the sensor’s view.
- Avoid having the sensor looking out the door entrance/exit. This can cause the sensor to detect people walking in the corridor by the open door and lead to undesirable results.
Ensure that tall furniture such as bookcases do not obstruct a sensor’s view. The lighting designer, through discussions with the owner, can help the owner "buy in" to using occupancy sensors in private offices, which are already required by the energy code for this sample project. It is helpful that a lighting designer explain to the owner how a past project’s issues may have been related to the incorrect placement of the occupancy sensors and that the new design will incorporate the correct placement of the sensors.
NFPA 70: National Electrical Code (NEC) has been adopted in all 50 states and is the benchmark for electrical design, installation, and inspection to protect people and property from electrical hazards. The NEC requirements for luminaires should be incorporated into the lighting system design. For example, the NEC requires in Article 110.26(D) that lighting in electrical rooms shall not be controlled by automatic means only, such as an occupancy sensor.
Buildings that are conforming to ASHRAE Standard 189.1: Standard for the Design of High-Performance Green Buildings are required to have occupancy sensors that automatically reduce lighting power in certain areas, such as a 50% reduction in hotel hallways, storage, and library stack areas.
Factor 4: Lighting levels
The IES is the recognized authoritative reference on the science and application of lighting. The IES Lighting Handbook is a guideline, not a code. It has an application section that provides recommended lighting levels based upon the type of space and the use of the space, as well as the age of the majority of the occupants in the space. Generally, the older the occupants, the higher the recommended lighting levels.
The lighting designer should use the IES Lighting Handbook to determine the lighting levels required for each space/room. There are several methods a lighting designer can use including software that can calculate the average, minimum, maximum, and ratios (maximum-to-minimum, average-to-minimum, etc.) of lighting levels.
Most lighting fixtures have an IES computer file that is used by lighting software to model and calculate lighting levels for a particular lighting fixture. A lighting designer should use the lighting fixture’s maintained lumens instead of initial lumens when using the IES file and modeling software. It is important that the IES file being used matches the configuration and options used for each lighting fixture.
The lighting designer can and should make appropriate variances to the guidelines in the IES Lighting Handbook for specific applications that have multiple variables.
Factor 5: Color temperature and CRI
Lately, many owners have been requiring their projects use LED lighting. These owners have heard that LEDs save money with their longevity and low maintenance costs. Does this mean that LEDs are the best solution?
The cost of LED light sources continues to lower over time while the efficacy (lumens per Watt) increases. But does this mean that LEDs are the right choice for every application?
Lighting designers should understand through the OPR what color temperatures and CRI to incorporate into the design. Most LEDs are most energy-efficient at higher color temperatures (more than 4,000 K). The lighting designer should choose the color temperature for each lighting fixture so that it aligns with the OPR and BOD. For example, lower color temperatures (2,700 K) would work well in a relatively dim bar with a central fireplace.
The color temperature should be the same for each area/room. Mixing color temperatures is not regarded as good design and can produce undesirable results.
The lighting designer also needs to ensure that the lighting compliance forms as well as any energy models (i.e., the LEED Minimum Energy Performance prerequisite) use the correct input wattage based upon the color temperature for the selected lighting fixture. For example, it is incorrect to choose the lower input wattage for an LED light source with a cool color temperature when completing a lighting compliance form when the lighting fixture with a warmer color temperature is selected and has a higher input wattage.
The lighting design shall also consider CRI when selecting light sources. Typically, the cost of a lamp increases as the CRI increases. The current CRI is a measure of eight (R1 to R8) color-reference samples, which are more pastel-colored. Many LED light sources have difficulty rendering saturated colors, such as strong reds. Color references R9 through R12 (saturated solids) are not measured in CRI, but the value of R9 (red) is important when specifying LED light sources.
CRI and R9 values should be dependent upon the type of environment the LED light source will be placed. Higher CRI (85+) and R9 (80+) values are generally required for retail environments. Strong red tones with the R9 value are prevalent in skin tones, clothes, meats, and store produce.
Projects that may be over the construction budget may include "value engineering" to reduce costs. It may be more cost-effective to use a light source like a ceramic metal halide lamp with high R9 color rendering than an LED light source with similar R9 color rendering.
Factor 6: ROI and lifecycle costs
ROI and lifecycle costs may be specified in the OPR. Many owners would consider a higher upfront cost for certain lighting fixtures and/or controls if a certain ROI is achieved.
Owners may request a lifecycle-cost analysis through the OPR. The lifecycle costs include the material costs required for replacement of lamps, ballasts, drivers, etc., including the labor costs for replacing these items.
For example, a building lighting renovation project is expected to last for 10 to 15 yr. Does it make sense to go with products that last at least 20 yr at a higher initial cost for this example? Instead, it may be better to use a less expensive product with a shorter useful life, but higher reliability. Sustainability also should be taken into account when choosing products based upon a longer useful life.
LED systems that have easy serviceability usually have a modular design that allows components to be replaced or upgraded easily. A technician’s time and rate for replacing parts should be accounted for in the lifecycle-cost analysis.
Factor 7: Safety and security
A lighting designer should confirm if the OPR contains safety- and security-related items. If it does not, the designer should ask that these items be added.
In our example, the OPR states that night lighting be installed at all entrance doors to the building. Night lighting typically means the lighting is to be on at night for safety and security as well as for convenience.
Codes may dictate that emergency lighting-either through a built-in battery pack, through a life safety system incorporating a generator and automatic transfer switch, or with an inverter-illuminate the path of egress inside and outside the building. The lighting designer needs to be aware of these codes (such as the local building codes) that require emergency lighting be installed.
Factor 8: Maintenance and warranty
A lighting designer should determine from the OPR the owner’s desires for maintenance and warranty. For example, how long is the desired warranty period? Longer warranties may increase project costs.
The maintenance of a lighting fixture should be considered by the lighting designer. A design may incorporate a low ballast factor along with a low-wattage fluorescent lamp. Will maintenance personnel know to use replacement ballasts and lamps with the correct specifications?
O&M manuals should be specified by the lighting designer to be provided to the owner by the contractor. The manuals should be reviewed by the lighting designer to ensure the correct lighting fixtures, controls, etc. cut-sheets and manuals. The information in the O&M manual should include the ballast and lamp criteria so a maintenance technician can install the correct parts.
Training should be provided to the owner’s maintenance staff and is usually found in the OPR. This training can help maintenance personnel understand group relamping and other recommended maintenance practices.
Michael Chow is the founder and owner of Metro CD Engineering. He holds a BSEE from Ohio Northern University, is a member of the Consulting-Specifying Engineer editorial advisory board, and is a 2009 40 Under 40 winner. Chow has won six IES Illumination Awards of Merit including four awards in 2015.