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.
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.
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.
To this end, both individual task lights and multi-occupant space lights must now have a dimmer or a mid-level setting in addition to turning “on” and “off.” This allows different users to get a higher level of lighting for focused tasks without needing to over-light the entire room—improving lighting quality while also saving energy.Additionally, the credit closes a major loophole from v2009 by ruling out controls that aren’t actually controllable by occupants. The new 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 rules out limited-access schemes in open offices, large event spaces, etc. where occupants had to request lighting changes through the building operations staff.
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.
Strategy A specifies fixtures with limited light output above the horizontal, 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?
In reality, although these seem like contradictory goals, they’re both just trying to keep people from looking directly at bright lights. Strategy A is really only concerned with fixtures that you can see from above, like pendant lamps in an atrium. If you don’t have a situation like this in your project, you should have no problems here.
The majority of spaces will fall into the requirements for Strategy D. Indirect lighting is a common strategy to evenly distribute high lighting levels by bouncing light off surfaces. This can reduce perceived contrast and make a room look brighter overall. Recessed troffer fixtures and can lights are still allowed for Strategy D as long as they don’t represent more than 25% of the lighting load. If recessed troffers are the primary lighting system in your project, you can always meet Strategy A without meeting Strategy D.
CRIColor-rendering index, or CRI, is a scale of 0 to 100, used by manufacturers of fluorescent, metal halide, and other non-incandescent lighting equipment to describe the visual effect of the light on colored surfaces. Natural daylight is assigned a CRI of 100. (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 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 fluorescent fixtures 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. Because Option B requires 100% of project lighting to meet the target CRI value, this option may be difficult for projects with a large amount of outdoor, garage, or back-of-house lighting.
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? As anyone who’s documented the Reduced Mercury in Lamps credit from LEED v2009 knows, 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 reducing long-term operational costs.
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 high-reflectance 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, LR values are higher for surfaces with lighter colors or glossier finishes, and lower for matte and darker surfaces. Finishes with higher LR values will bounce more light and appear brighter than those with lower LR values.
Both of these strategies are great for spaces with lower lighting levels and are relatively easy to pursue. But if your project is over-lit through too much electric lighting or daylight, adding more reflective finishes may actually increase glare and cause problems for visual comfort. This is a consideration that should be assessed in tandem with the intended aesthetic, use, and lighting strategy of the space.
Illuminance Ratios (Strategies F and G): 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 F (for walls) and G (for ceilings) are based on illuminance ratios, a way of comparing illuminance levels from different surfaces to predict this type of eyestrain.
These are the most intensive strategies included in this credit because they require detailed lighting measurements or simulation to determine the illuminance ratios in regularly occupied spacesEnclosed space intended for human activities, excluding those spaces that are intended primarily for other purposes, such as storage rooms and equipment rooms, and that are only occupied occasionally and for short periods of time. Occupied spaces are further classified as regularly occupied or nonregularly occupied spaces based on the duration of the occupancy, individual or multioccupant based on the quantity of occupants, and densely or nondensely occupied spaces based on the concentration of occupants in the space.. However, they are also the most rigorous ways of determining whether or not lighting schemes will actually provide even, high-quality lighting. Just like with an energy or daylight model, pursuing the calculations for either of these two strategies will be more valuable if adopted early in the design process.
Look on the manufacturer’s specification sheet. It’s a separate measurement from color temperature and light intensity.
Adjustable lights are excluded from the requirements for direct vs. indirect lighting but do need to be included for CRI and lamp life.
The requirements aren’t too unreasonable and can be achieved by balancing out darker colors with glossier textures (or vice versa). In fact, the reflectance values in this credit are on par with those listed as “default” finishes for evaluating daylighting in Core & Shell buildings. Because the thresholds are based on an area-weighted calculation, there’s also some flexibility in selecting accent materials and providing variety that way.
The controls, lamp specifications, and surface reflectance strategies are all appropriate for spaces that incorporate daylighting and will even help with your daylighting strategy.
A high level of controllability provides an opportunity for energy savings when there is enough daylight to meet occupant needs, and high surface reflectance values will likely increase the reach of existing daylight. High-CRI lights will blend in well with high-CRI daylight. The illuminance ratios in Strategies F and G may be more complicated to pursue, but if the daylight model indicates that glare is a big concern, it might be a good idea for your design to take a closer look at illuminance levels in the occupants’ fields of view.
No. The contribution of daylight is excluded from the three lighting level requirements in lighting controls. Lighting systems must be able to meet the controllability requirements separate from any operable shades. This applies to both individual workstations and multi-occupant spacesMulti-occupant spaces are places of egress, congregation, or where occupants pursue overlapping or collaborative tasks. Multi occupant spaces may be regularly or non-regularly occupied spaces..
Yes, as long as having only one circuit on provides between 30%–70% of the maximum lighting level.
In some spaces with simple geometry, you can actually perform these calculations by hand (see the IESNA handbook for formulae and more details). You can even measure them directly using a photometer. There are also some lighting design and daylighting simulation programs that perform these calculations. Look for a program that runs on a radiosity or ray-tracing engine, will model point source lighting, and will calculate illuminance on any specified plane.
To promote occupants’ productivity, comfort, and well-being by providing high-quality lighting.
Select one or both of the following two options.
For at least 90% of individual occupant spacesIn individual occupant spaces, occupants perform distinct tasks from one another. Such spaces may be contained within multi-occupant spaces and should be treated separately where possible. Individual occupant spaces may be regularly or non-regularly occupied spaces., provide individual lighting controls that enable occupants to adjust the lighting to suit their individual tasks and preferences, with at least three lighting levels or scenes (on, off, midlevel). Midlevel is 30% to 70% of the maximum illumination level (not including daylight contributions).
For all shared multioccupant spaces, meet all of the following requirements.
Choose four of the following strategies.
A sample cutsheet shows the kind of data you'll need to document light reflectance values (LRV) for interior products.
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