This Radiance simulation for the Sustainability Base at the NASA Ames Research Center in Moffet Field, California, predicts illuminance levels throughout the interior. Image – Loisos+UbbelohdeA space with good daylighting is healthier, more pleasant, and more productive for occupants. Making use of more daylight also means less reliance on electric lighting, which can account for a significant portion of total energy use in many building types.
This credit is often targeted as it has a number of synergies with other LEED credits, including EQc8: Quality views, EQc6: Interior lighting, EAc2: Optimize energy performance, IPc1: Integrative process, and SSc1: Site assessment.
Discussing daylighting considerations early in the design process is key for achieving this credit because the design choices that have the biggest impact on daylighting are typically made early in the project timeline. These include choices like building shape, orientation, and window-to-wall ratio.
The three options available for this credit each reference different industry metrics and methodologies. As with other LEED credits, compliance paths that are more challenging or require greater effort but that bring more precision are worth more points.
Conducting a full annual computer daylight simulation is likely the best option for most projects. Compared to the other options, it offers more potential points and provides a better understanding of the daylighting performance of the space without requiring any significant extra modeling efforts.
The two metrics in this option, both calculated over the course of a full year, represent opposing design targets that must be balanced to achieve high-performance daylighting. sDA(Spatial Daylight AutonomyA metric describing annual sufficiency of ambient daylight levels in interior environments. It is defined as the percentage of an analysis area (the area where calculations are performed, typically across an entire space) that meets a minimum daylight illuminance level for a specified fraction of the operating hours per year (i.e., the Daylight Autonomy value following Reinhart & Walkenhorst, 2001). The illluminance level and time fraction are included as subscripts, as in sDA300, 50%. The sDA value is expressed as a percentage of area.) is intended to measure the amount of area that receives enough daylight for people to work comfortably without additional electric lighting. sDA300/50% is defined as the percentage of the analyzed space receiving at least 300 luxMeasurement of lumens per square meter., or 28 footcandles, for at least 50% of annual occupied hours.
ASE(Annual Solar Exposure) is a measure that indicates the amount of area that receives too much direct sun over the course of the year. ASE1000/250 is defined as the percentage of the analyzed space that receives above 1,000 lux for 250 occupied hours or more in a year. To meet credit requirements, the ASE threshold must be met for each individual space, or at most, for each separate floor.
Illuminance is a basic measure of how much light an area is receiving at a particular point in time, measured in foot candles or lux. Illuminance is a useful metric for lighting designers and architects who need to visualize how the space will be experienced at any given moment. For Option 2, fewer points are available because illuminance levels are required to be modeled for only two points on a single day (9 a.m. and 3 p.m. on the equinox), which gives a less complete indication of the daylighting performance than a full annual simulation. As part of a credit compliance strategy, this can be a good backup option because buildings that don’t meet the thresholds of Option 1 might still meet Option 2. It may also provide flexibility in selecting a daylight modeling program, since the calculations for ASE and sDA are more advanced.
Option 3 is also based on illuminance, but measurements are taken during occupancy at two different times within a year instead of modeled in advance. Note that although the measurements don’t need to be at any specific time of year, they must be several months apart. The measurements must also be taken post-occupancy, after all furniture and glare control devices are installed, which may cause coordination problems.
Building orientation: A thin building with a long axis oriented east-west will be the best starting position for good daylighting. Keep in mind that for many latitudes, daylighting will reach a depth into the space of about 1.5 to 2 times the window head height.
Window-to-wall (WWR) ratio: There is no single “best” window-to-wall ratio for daylighting, because the WWR impacts the balance between spatial daylight autonomy and direct sun, which can bring heat and glare. WWRs of 30%–50% are typically sufficient for good daylighting, while higher ratios (think all-glass façades) generally create problems for managing the additional direct sunlight.
For optimal design, the WWR should vary on different walls depending on orientation and climate. In the northern hemisphere, southern walls benefit from high WWR as long as they are adequately shaded (in the southern hemisphere, northern walls should be shaded). Northern walls with high WWR are great for providing diffuse daylight without glare. Eastern and western windows can be tricky to shade and can therefore cause significant glare problems. In general, eastern and western walls should have a low WWR.
Roof overhang/horizontal louvers: Horizontal shading elements, such as roof overhangs and louvers, can be very effective at reducing direct sunlight penetration around midday. However, horizontal shading is not as effective at blocking morning or afternoon sun on the eastern and western facades. For most latitudes, horizontal shading is not typically necessary on the facade opposite the sun (north in the northern hemisphere, south in the southern hemisphere).
Vertical fins: In higher latitudes, vertical shading elements are generally more effective at blocking eastern and western sun than horizontal elements.
Light-appropriate programming: Only 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. are analyzed for this credit. Even with the best building design, it is likely that some spaces will either be lacking in daylight autonomy or will get too much direct sunlight. This isn’t a problem if those spaces aren't areas where people spend time working or studying. Darker interior areas can be used for stairs or elevators, bathrooms, storage closets, copy rooms, video conferencing rooms, or similar areas.
Private offices at the perimeter reduce the daylight that penetrates into common areas. Selecting glass partitions can compensate for this, but avoiding this situation early on by placing private offices in the interior is ideal. Perimeter areas with too much direct sun can be difficult to program, but using those areas as circulation space or break areas can be good options.
Reflectance values: Choosing materials with higher reflectance values (such as lighter paint colors or lighter wood tones) will bring daylight further into the space.
Visual light transmittance (VLT) values: Reducing the VLT value of the exterior glazing to manage glare will decrease visible light levels in the building. Unfortunately, in most cases, reducing the VLT will have a much larger practical impact on beneficial daylight autonomy than on reducing undesirable direct sun. Therefore, low VLT glazing should not be a primary strategy for dealing with direct sun.
Separate daylight and vision glazing: The optimal configuration for views and daylighting are not necessarily the same. By separating both functions, you can manage daylight without sacrificing views through selecting separate glazing specifications or control strategies.
Estimated construction costs for key daylighting strategies Source – BuildingGreen's Cost of LEED v4 ReportLight shelves: Interior light shelves can be a good strategy for optimizing daylight because they both reduce direct light near a window and also increase reflected light levels further into a space, potentially doubling the depth of daylight penetration. Although they can be beneficial, light shelves alone won’t usually have a large enough impact to save a building with poor daylighting. Instead, they should be used in conjunction with other elements of good design as a means for further enhancing daylighting in a space.
One important thing to keep in mind is that manual glare-control devices, such as blinds, are required for all regularly occupied spaces regardless of the outcome of the daylight analysis.
But, these must be excluded when determining glare through computer modeling. This means that blinds cannot be the only form of glare control employed in the building, and teams need to mitigate glare through other design methods.
Circadian rhythmThe rhythm of an organism's vital functions with relation to the daily cycle of the natural environment. is another lighting design consideration worth discussing with the project team. Exposure to certain amounts and frequencies of light trigger chemical responses in the human body that help regulate one’s daily biological clock. Proper lighting design can help occupants be awake and alert during the day and sleep better at night. Electric light fixtures can contribute to a healthy circadian rhythm, but not surprisingly, our bodies respond more strongly to the wavelengths of natural daylight.The WELL Building Standard is a good source for additional information about circadian lighting design.
Although this was acceptable for LEED v2009 projects because thresholds were added to each type of compliance method, you will now need to just pick one option to follow. If your modeling program allows, try out both thresholds to see what will be more beneficial for your project.
No. The compliant square footage would be the worst-case scenario between the two times. For example, a 900 ft2 space located on the western side of a building is 100% compliant at 9 a.m. but only 50% compliant at 3 p.m. The compliant square footage in this case is 450 ft2.
It’s not a requirement to model any type of furniture, and in general it’s recommended to start modeling before the furniture layout is finalized in order to have the best chance for success. However, if there are concerns that there might not be enough light on desks with the high partitions, or even if the high partitions are part of a glare mitigation strategy, they can be included.
Glare control devices need to either be controlled manually or have a manual override to accommodate different individual preferences for lighting levels. In other words, they have to be real controls! For this reason, while exterior fixed overhangs and louvers can be helpful in achieving daylighting thresholds, you’ll still need to provide glare control devices that are accessible to occupants to comply with credit requirements.
Yes, you’ll need to complete this calculator if you’re attempting either credit. You’ll also need to submit a summary report from your daylight modeling program, or floor plans showing measurements taken if pursuing Option 3. Either report should confirm the compliant floor area in each space.
The LEED v4 Reference Guide has additional guidance on how to classify spaces and how to determine which spaces are included for each IEQ credit. For this credit, daylight modeling or measurements must be conducted in all regularly-occupied spaces, which is any place where people spend an hour or more per day conducting typical activities. Regularly-occupied spaces that are only used for video presentations, like teleconferencing rooms or auditoriums, can be excluded from this credit.
LEED doesn’t require certain software to run the compliance calculation. However, the simulation should be able to run under “clear sky” conditions and calculate illuminance levels at 2'–6" above finished floor (AFF).
To connect building occupants with the outdoors, reinforce circadian rhythms, and reduce the use of electrical lighting by introducing daylight into the space.
Provide manual or automatic (with manual override) glare-control devices for all 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..
Select one of the following three options.
Demonstrate through annual computer simulations that spatial daylight autonomy300/50% (sDASpatial daylight autonomy: a metric describing annual sufficiency of ambient daylight levels in interior environments. It is defined as the percentage of an analysis area (the area where calculations are performed, typically across an entire space) that meets a minimum daylight illuminance level for a specified fraction of the operating hours per year (i.e., the Daylight Autonomy value following Reinhart & Walkenhorst, 2001). The illluminance level and time fraction are included as subscripts, as in sDA300, 50%. The sDA value is expressed as a percentage of area.300/50%) of at least 55%, 75%, or 90% is achieved. Use regularly occupied floor area. Points are awarded according to Table 1.
Demonstrate through annual computer simulations that annual sunlight exposureA metric that describes the potential for visual discomfort in interior work environments. It is defined as the percentage of an analysis area that exceeds a specified direct sunlight illuminance level more than a specified number of hours per year.1000,250 (ASEAnnual sunlight exposure: a metric that describes the potential for visual discomfort in interior work environments. It is defined as the percentage of an analysis area that exceeds a specified direct sunlight illuminance level more than a specified number of hours per year.1000,250) of no more than 10% is achieved. Use the regularly occupied floor area that is daylit per the sDA300/50% simulations.
The sDA and ASE calculation grids should be no more than 2 feet (60 cm) square and laid out across the regularly occupied area at a work plane height of 30 inches (76 cm) above finished floor (unless otherwise defined). Use an hourly time-step analysis based on typical meteorological year data, or an equivalent, for the nearest available weather station.
Include any permanent interior obstructions and movable furniture and partitionsMovable furniture and partitions are those that can be moved to provide access to the view by the user without the need for tools or assistance from special trades and facilities management..
Demonstrate through computer modeling that illuminance levels will be between 300 luxMeasurement of lumens per square meter. and 3,000 lux for 9 a.m. and 3 p.m., both on a clear-sky day at the equinox, for the floor area indicated in Table 2. Use regularly occupied floor area.
Calculate illuminance intensity for sun (direct component) and sky (diffuse component) for clear-sky conditions as follows:
Exclude blinds or shades from the model.
Include any permanent interior obstructions and movable furniture and partitions.
Achieve illuminance levels between 300 lux and 3,000 lux for the floor area indicated in Table 3.
With furniture, fixtures, and equipment in place, measure illuminance levels as follows:
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