Interior Lighting in LEED v4 is much more holistic than its rough equivalent in prior versions of the rating system. This credit aims to bring visual comfort in LEED-certified buildings up to the same standards applied to other aspects of the interior environment, such as thermal comfort and indoor air quality. That’s because occupants in spaces with high-quality lighting tend to be more satisfied with the overall indoor environment, more alert and productive during the day, and healthier over time.
On the surface, it looks like there’s a lot in this credit to take in, but its mix-and-match approach ultimately provides flexibility.
Note that this credit covers only electrical lighting; a separate but complementary credit, EQc7, deals with natural daylighting.
We’ll start by going through the metrics and terminology, and then think about when and how to actually apply all this.
Not In the LEED Reference Guide
Check the credit language and the LEED Reference Guide for more technical detail on this credit appropriate for lighting designers. Here we’ll provide less-technical background and context.
Option 1: Lighting control for occupants
Have you ever been in a situation where you couldn’t see a presentation, only to have the speaker dim the lights so much that you couldn’t take notes? Option 1 of the credit aims to resolve everyday problems like this one, where different occupants in a shared space might have different lighting needs at the same time.
This option has separate criteria for individual occupant spaces and multioccupant spaces. However, project teams should be careful to review the space type categories at the beginning of the EQ section in the Reference Guide before developing an approach here. Some spaces, like individual workstations in an open office, fall under the “individual occupant” category and require above-and-beyond standard practice to comply.
The requirements for multioccupant spaces generally align with ASHRAE 90.1-2010, so projects should have no problem meeting these criteria. General lighting should be separated into multiple zones and be able to provide at least three different lighting levels. The credit language makes it clear that users need to be able to watch the lighting respond while flipping the switches in order for the lighting system to qualify for the credit. This closes a major loophole from LEED 2009 by ruling out limited-access schemes in open offices, large event spaces, etc. where occupants had to request lighting changes through the operations staff, which meant that the lights weren’t actually controllable by occupants.
Each individual occupant space must also have its own lighting controls with at least three different lighting levels. For separate rooms such as private offices, this may be accomplished at the room level. For larger spaces with individual workstations, individual fixtures must be provided for each workstation. This can be accomplished with task lights that have at least three settings (on-off isn’t enough!) or through a more complex building-integrated control system with individually-controllable overhead lighting.
Option 2: Selecting fixtures for better light quality
This Option requires the team to pick 4 of 8 strategies.
The first four “lighting quality” choices (A through D) have to do with the specifications of individual fixtures. Lighting designers can take care of these requirements when developing the fixture schedules. To document the credit requirements, include the number of fixtures, space type, and connected load per fixture in the schedule for each fixture type. The second four (E through H) relate to the surface reflectance of the space and/or furnishings, which generally fall under the interior designers’ purview.
Direct vs Indirect Lighting (Strategies A and D)
Strategy A specifies fixtures with limited light output above the diagonal, while Strategy D favors the use of indirect fixtures. Any fixtures that meet Strategy D are excluded from the requirements of Strategy A. So what’s the actual impact of choosing to pursue both of these, and what should be emphasized?
Glare mitigation (Strategy A): Strategy A is intended to reduce glare into the luminaire either from below or above. In general, this requires that fixtures have a limited luminous intensity (measured in candelas) from 45 degrees away from the fixture. If this information is not listed on cut sheets, it may need to be read from the manufacturer’s IES file.
Remember, all the calculations are in installed watts, and should cover only regularly occupied spaces. Be careful to make sure that the space classifications and areas in this credit match the rest of your LEED application. Fixtures in non-regularly occupied spaces are therefore excluded. Fixture types that do not need to be added to the wattage total in the calculations include wall washers, adjustable fixtures (such as task lamps), or indirect fixtures which are not visible from above.
Uplighting (Strategy D): promotes the use of uplighting. Uplighting reduces perceived contrast to make a room look brighter and reduce eye strain. For true uplights, 100% of the wattage should be included. For direct-indirect fixtures, the wattage should be prorated based on the percentage of uplighting only—so a fixture that has 10% downlighting and 90% uplighting would contribute only 90% of its wattage towards the overall requirement.
CRI and Rated Life (Strategies B and C)
CRI (Strategy B): CRI, or Color Rendering Index, is a measurement of the ability of a light source to accurately re-create colors when compared with sunlight. This in turn depends on the fullness of the light spectrum. While low-CRI sources tend to provide a desaturated or even greenish light (think of old tube fluorescents), high-CRI sources provide a true color. CRI has become an important index for measuring LED lighting quality, which varies greatly, and the 80 CRI target in the credit requirements aligns with the Energy Star specification for LED lighting.
Many newer fluorescent lamps also meet these requirements, and it’s worth the effort to find them for any spaces where visual tasks are important. However, it’s much harder to find high-intensity lighting that meets the CRI requirements, making this requirement more difficult for projects with a large amount of outdoor metal halide or HID fixtures. If your project has a lot of outdoor or garage lighting, opt for LEDs to meet these requirements and save some energy!
Rated Life (Strategy C): Choosing lamps with a long rated life is good for the environment and good for the wallet, but how does it contribute to lighting quality? Because the light output of a fixture actually changes over time, lamps with longer rated lifespans are better able to maintain design lighting levels. A rated life of 24,000 hours is a reasonable benchmark for a high-quality fluorescent lamp, while a good LED lamp should have a rated life of about 50,000 hours. This strategy makes sense to pursue on any project interested in lower utility costs, better lighting quality, and less maintenance.
Maximizing light in a space (Strategies E through H)
The second four “lighting quality” choices (E through H) focus on strategies for optimizing lighting through choice of interior surfaces. You can have as many great lighting fixtures as you’d like, but once light leaves the fixture, it’s down to the interior design of the space to create a visually comfortable environment.
Surface Reflectance (Strategies E and F): These two strategies are about selecting appropriate reflectance values for architectural and furniture surfaces in order to create even light levels. Request Light Reflectance Values (LRV) from finish (Strategy E) and furniture (Strategy F) manufacturers or find them on specification sheets. As a rule of thumb, LRVs are higher for surfaces with lighter colors or glossier finishes, and lower for matte and darker surfaces. Finishes with higher LRVs will bounce more light and appear brighter than those with lower LRVs. Many paint and ceiling tile manufacturers list the LRV on product data sheets, but for carpet or other fabric wall covering, you may have to request this data.
Both of these strategies are great for spaces with lower lighting levels, as lighter surfaces can improve the way humans “see” light, and are relatively easy to pursue. Lighter surfaces and finishes are easily specified, and the credit still allows room for accent materials. This strategy should be assessed in tandem with the intended aesthetic, use, and lighting design of the space.
Illuminance Ratios (Strategies G and H): Having a high difference in illuminance on surfaces in the same view can cause glare and eye strain. Imagine a glowing screen in a dark room compared to a glowing screen in a bright room: the screen is still giving off the same light, but it looks way too bright when you’re in the dark. Strategies G (for walls) and H (for ceilings) are based on illuminance ratios, a way of comparing illuminance levels from different surfaces to predict this type of eyestrain.
Spaces that have to comply with requirements
What spaces need to comply with lighting requirements?
In this credit, different options apply to different space types. Depending on your project needs, you may want to select the options which work best for your lighting design.
High-CRI lighting (Option 2, Strategy B) and high rated life for lamps (Option 2, Strategy C) apply to all spaces in the project. Option 1 and Option 2, Strategies A and D–H apply to regularly occupied spaces only, leaving more flexibility for design accents in non-regularly-occupied transition spaces such as corridors. Option 1 has separate requirements for both regularly occupied individual and multi-occupant spaces, but the Option 2 strategies do not make a distinction, which may limit design flexibility for spaces like conference rooms. See the table for another view of this.
What’s New in LEED v4.1
Should I Upgrade?
This credit is unchanged between v4 and v4.1, so there is no reason to do a one-off credit upgrade.