D.7.2  Lighting System Design

The architectural design of a high-performance building maximizes the use of daylighting in the building. The engineering design integrates the electric lighting system design with the architectural design to supplement the changing daylighting levels and maintain constant prescribed lighting levels in the space, using the most efficient lighting technologies and control strategies available. Always design the lighting system before designing the HVAC system.
The first step in lighting design is to determine the visual needs of the space and identify what type of lighting to use. Lighting types are divided into four categories:

  • Ambient lighting - typically used for circulation and general lighting to give a “sense of space.”  Design ambient lighting systems before designing systems to accommodate the other lighting types.

  • Task lighting - used where clearly defined lighting levels are required to complete detailed work, such as paperwork, reading, or bench-top experiments.

  • Accent lighting - used for architectural purposes to add emphasis or focus to a space or to highlight a display.

  • Emergency or egress lighting - used to provide a pathway for exiting a building if an emergency arises.

D.7.2.1  Ambient Lighting

Ambient lighting systems can be easily integrated with the available daylighting. In a well-designed building, daylighting can offset most or all of the daytime ambient lighting loads. Use the following four steps to design ambient lighting systems.

  • Define the daylighting zones. Evaluate the location of the windows. Align the daylighting zones parallel to the windows with breaks at 5 feet, 10 feet, and 20 feet away from the windows. Place zone separations at corners where windows change orientation. Also, carefully evaluate the daylighting penetration into private offices or other small, enclosed rooms. Light levels measured in daylighting zones will determine how much electric lighting is needed to supplement the daylighting.

  • Define the occupancy zones. The occupancy zones do not necessarily have to match the daylighting zones. The occupancy zone is typically a room, such as a private office or a group of open offices. The sensors located in the occupancy zones turn the electric lights on when the daylighting is not sufficient to meet the prescribed luminance level if there are people in the zone.

  • Determine the minimum ambient lighting levels. Design a lighting system to complement the available daylighting in each occupancy zone. The space use will determine how much ambient light is needed (refer to the Illuminating Engineering Society of North America (IESNA) guidelines for detailed lighting level recommendations). The ambient lighting level in good daylighting designs may be less, but provides an equivalent feeling of brightness, than the level conventionally specified for a nondaylit space. Strive to design for less than 0.7 W/ft2 for ambient lighting system power densities. Guide-lines for determining ambient lighting levels are:

  • Provide lower ambient lighting levels in private offices and other areas where the occupants rely on task lighting to complete most of their work.

  • Provide higher ambient lighting levels in densely occupied work areas. Distribute the ambient light uniformly in these spaces from directions that will minimize glare and reflections on the work surface. For example, position workstations between the rows of ceiling-mounted luminaires. Light coming from the sides of rather than directly in line with the viewing direction will reduce veiling reflection potential.

  • Plan for fluctuating lighting levels in daylit circulation spaces, as long as the minimum lighting levels allow for safe movement when there are people in the space. All circulation spaces can have sensors to turn the electric lights off when daylight is available or when the space is not occupied.

  • Be cautious that a common lighting design error is to supply too much electric light to an area. Proper lighting levels lead to less energy-intensive electric lighting systems and introduce less waste heat into the space, which in turn decreases the space cooling loads.

  • Select lighting fixtures. Fixture designs can provide high lighting efficiency while also meeting the other lighting objectives of the installation. Use efficient fixtures with appropriate distribution, glare control, and visual characteristics for the lowest possible power input. Work with the architectural designers to select fixtures that achieve the desired ambient quality while minimizing lighting energy requirements. Also, select fixtures that are capable of dimming the light output so they only supply the light needed to supplement available daylight.

  • Direct, ceiling-recessed fixtures are commonly used in office and laboratory spaces; however, their use is discouraged because of poor lighting quality. If these fixtures must be used with a ceiling plenum-type return air stream, select fixtures with heat removal capabilities. The light output of fluorescent lamps decreases when operating at temperatures higher than room temperature. Ventilated fixtures help keep the lamps at a lower temperature, thereby allowing the lighting equipment to operate more efficiently by directing some of the heat from the lamps into the return air stream instead of into the space.

  • Indirect lighting fixtures provide very uniform light levels, eliminate excessive reflections on the task, and minimize shadows (especially from the head and hands). They provide good flexibility for future space rearrangements because of the uniform light level. Indirect lighting fixtures use about 15 percent more energy than direct fixtures to achieve a given lighting level because the light must bounce off the ceiling. However, indirect lighting fixtures provide a better quality of light, so the lighting levels and power densities can be reduced.

  • The recommended lighting fixture for most Fort Carson applications combines the direct and indirect approaches. These fixtures provide both upward and downward light. Their efficiency is about equal to a good direct lighting fixture with the uniformity and glare control of indirect lighting. The direct portion can provide some brightness and adequate shielding to provide good visual comfort and avoid glare. Ideally, the indirect portion does not create hot spots or excessive luminance on the ceiling. Typically, the best direct portion is 20 percent to 50 percent of the light, while the remainder is indirect.

Click to enlarge image
Direct and Indirect Lighting

Select direct/indirect fixtures that allow airflow through the fixture past the bulbs to minimize dirt accumulation. Note that not all direct/indirect fixtures are designed to resist dirt accumulation.


D.7.2.1.1  HID Lighting

Standard HID lamps do not work well with daylight or occupancy controls because of the long starting and restrike times. Consider HID lighting in high bay areas with no daylight that need to be continuously illuminated, and for exterior applications.

D.7.2.1.2  Fluorescent Lighting

Fluorescent lighting is the best type of lighting for most applications at Fort Carson (usually linear fluorescent lamps). It can be easily controlled and integrated with the daylighting design. Linear fluorescent lamps are classified by tube diameter, wattage, color rendering index (CRI), and color temperature, where:

  • Tube diameter is measured in 1/8" increments (e.g., the diameter of T-8 lamps is 1" and the diameter of T-5 lamps is 5/8").

  • Wattage is the power required to operate the lamp. The wattage is usually stamped on the lamp itself or on the package in which the lamp is shipped. Note that the lamp wattage is different from the system wattage, which includes auxiliary equipment such as the ballasts.

  • CRI is the ratio of the light source to a standard reference source. A CRI of over 80 for a fluorescent lamp is considered very good color rendering, while some high-pressure sodium (HPS) lamps have CRIs in the 20s.

  • Color temperature gives a general idea of the visual color of the lamp (warm - more red - 2000 to 3000 K, or cool - more blue - 4000 K and above), while color rendering is how accurately a lamp renders colors in the environment.

 

D.7.2.2  Task Lighting

Task lighting provides additional illumination to areas where individuals perform difficult visual tasks, such as working at a desk or completing detailed laboratory activities. Steps to designing good task lighting systems are:

  • Determine where task lighting is needed. To achieve the most energy savings, use separate lighting fixtures to provide additional task lighting only where the building occupants need it instead of depending on the ambient lighting system to provide enough light to complete detailed tasks.

  • Balance task and ambient lighting levels. To help maintain visual comfort, the task illumination must not be more than three times that of the ambient illumination.

  • Provide automatic and manual controls. Task lighting is best controlled with occupancy sensors and manual user controls.

 

D.7.2.3  Accent Lighting

Accent lighting highlights aesthetic features in the space or give the space a certain desired “feel.” Accent lighting system design guidelines are:

  • Limit the amount of accent lighting. For the amount of useful light it provides, accent lighting often consumes more power than ambient or task lighting systems.

  • Use occupancy sensors to control accent lighting. Ensure that the accent lighting is on only when there are people in the space.

  • Select low-energy fixtures. Select the lowest-wattage fixtures possible to achieve the desired effect for all accent lighting.

  • Balance accent and ambient lighting levels. Reduce the ambient lighting levels near accent lighting to improve contrast.

 

D.7.2.4  Safety Lighting

Safety lighting (sometimes called “emergency lighting”) allows people to enter a space, occupy it, and move through or exit it without endangering their physical well-being. Building codes require that potential hazards, circulation areas, entrances, and exits must be illuminated. Guidelines for designing safety lighting systems are:

  • Select low-energy safety lighting fixtures. Use high-efficacy lamps in efficient fixtures and provide safety lighting only to the required lighting level.

  • Operate safety lighting only when needed. Use occupancy sensors and photo sensors to control safety lighting.

  • Place all safety lighting on separate lighting circuits. Separating circuits leads to the ability to turn off the safety lighting when it is not needed.

 

D.7.2.5  Lighting Controls

Lighting controls match the light output to the occupancy schedule and illumination requirements. The controls minimize the actual energy consumption without compromising the quality of lighting in the space. There are two types of controls:

  • Manual controls are appropriate for spaces that have lamps with long starting and restrike times, such as high-intensity discharge (HID) lamps. They may also be appropriate for spaces that require occupant light control, such as equipment rooms and laser laboratories; however, manual controls are usually not recommended.

  • Automatic controls are more appropriate for spaces where daylighting is the primary lighting source and spaces having differing occupancy schedules, such as offices, break rooms, and restrooms.

On-off or step-function lighting controls are best suited for spaces where occupants are in the space for a short period or when sudden shifts in lighting levels will not disturb the occupants. Circulation areas, restrooms, interior laboratories, and service rooms are good candidates for on-off or step-function lighting controls. These lighting control functions can be either manual or automatic.
Dimming function lighting controls are best suited for blending electrically generated light with daylight to provide the designed illumination level. Conference rooms and interior private offices with no daylighting are examples of the few places where manual dimming is appropriate. In these special cases, an occupancy sensor turns the electric lights on and off and the occupants may have manual dimming controls to set the lighting at the appropriate level.
The best dimming controls are automatic and continuous. Continuous dimming avoids instantaneous jumps in lighting levels that can be distracting to the occupant. Ideally, the lighting control system is capable of dimming the lights based on lighting level, and turning off the lights if the space is unoccupied.

 

D.7.2.6  Steps for Effective Lighting System Design

1. Review the F&OR document for the space use description.

2. Define the reason for the lighting.

Ambient - circulation and general lighting

Task - areas where detailed work is done

Accent - architectural use only (minimal)

Safety or emergency egress lighting

3. Design the ambient lighting system.

Define daylighting zones

Define occupancy sensor zones

Determine minimum ambient lighting levels

Select lighting fixtures

4. Design the task lighting system

Determine where task lighting is needed

Balance task and ambient lighting levels

Provide automatic and manual controls

5. Design the accent lighting system.

Limit the amount of accent lighting

Use occupancy sensors to control accent lighting

Select low-energy fixtures

Reduce, ambient light levels when there is accent lighting

6. Design the safety lighting system.

Select low-energy safety lighting fixtures

Operate safety lighting only when needed

Place all safety lighting on separate lighting circuits

7. Verify the design by evaluating lighting power densities W/ft2.

 

Appendix D.7  Lighting, HVAC, and Plumbing