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IDL - Bozeman eNEWS - April 2013 - Vol. 6 No. 4

Entries in daylighting (12)


Daylighting and LEED v4: What this means for design and allied professionals

As of July 2013 the USGBC voting body overwhelmingly approved the new LEED v4 rating system.  In November the new rating system will be launched at the Greenbuild Conference in Philadelphia.  Introducing the system will be Scot Horst, Vice-President of LEED at the USGBC.  At the conference LEED will present updated v4 exam information, reference guides, and educational resources.  More information about the conference and its schedule can be found on the Greenbuild website listed below.  With change there comes dire speculation about how the new rating system will be implemented.  Beginning in November, LEED v4 and LEED 2009 will concurrently accept applications for project certification.  LEED 2009 will accept applications until June 1, 2015, at which time LEED v4 will become the exclusive certification rating system.  Most importantly, however, the major question most design professionals and members of the allied professions are asking themselves is, “What does this mean for me?”  In response the Bozeman Integrated Design Lab is examining the new Daylighting credit structure.  Provided is a basic summary of what has changed in the Daylighting credit for those professionals seeking LEED v4 certified projects.


The changes to the daylighting credit are, for the most part, relatively simple.  Most obviously is that the daylighting and view credits previously known as IEQ Credit 8.1: Daylight and Views-Daylight, has become simply EQ Credit: Daylight.  “Views” is now a separate credit.  Within this v4 credit, there are a few structural changes.  First, the illuminance units have been switched from the English unit “footcandles” (fc) to the SI-unit “lux”.  Additionally, the acceptable illuminance value range has been narrowed to 300-3000 lux (approximately 28 fc to 280 fc).  Another important change is the elimination of “Option 2. Prescriptive” as a choice for the verification of daylighting values.  This option has been replaced by a new simulation called “Spatial Daylight Autonomy and Annual Sunlight Exposure.”  Spatial daylight autonomy (sDA) is a standard requiring 50% of occupiable hours during the year be adequately daylit in a project (between 300-3000 lux).  The caveat, however, is controlling Annual Sunlight Exposure (ASE), which is the percentage of square footage in regularly occupied spaces that has direct sunlight during the year.  LEED v4 will require that illuminance values of 1000 lux and above must not exceed 250 occupied hours during the year, and must not exist in more than 10% of the occupiable floor area.  Occupiable hours will be typically considered between 8 a.m. and 6 p.m.  Two points can be gained if the sDA value is achievable in 55% of regularly occupied space, and three points can be gained if the sDA value is achievable in 75% of occupied space.  The hierarchy of points has been carried through to the other two traditional LEED 2009 verification options: “Illuminance Calculations” and “Measurement.” 


While these changes are topical, they will certainly require familiarization.  In order to help mitigate confusion, Figure 1.illustrates some of the new terminology in the daylighting credit, and Figure 2.breaks down the new hierarchy of points.  The Integrated Design Lab in Bozeman is committed to aiding design and allied professionals understand the possibilities for designing with daylight regardless of LEED certification.  However, the lab welcomes your questions and advice on the new LEED v4 rating system.  In future e-news sections, the lab will be addressing changes to the views credit in v4 as well as following up on information that emerges from v4’s implementation.




Spatial Daylight Autonomy

     LEED v4 Abbreviation: sDA 300, 50%

*Standard that requires 50% of occupiable hours during the year be adequately daylit


*In the LEED v4 abbreviation “sDA 300, 50%” the “300” is the lux value and the “50%” percentage of occupiable hours.  Therefore sDA 300 lux, 50% of occupiable hours

Annual Sunlight Exposure

     LEED v4 Abbreviation: ASE 1000, 250

*Standard that requires regularly occupied spaces to not have too much direct sunlight, which causes glare and can increase cooling loads


*In the LEED v4 abbreviation “ASE 1000, 250” the “1000” is the lux value considered direct sunlight and the “250” is the maximum number of occupiable hours direct sunlight can be present in an area.  Therefore ASE 1000 lux, 250 hours

Figure 1. Terminology of Option 1: Simulation



NC, CS, Schools Retail, Data Centers, Warehouses and Distribution Centers, Hospitality

sDA (regularly occupied floor area)

Points Possible

55 %


75 %




Calculation: Regularly Occupied, Daylit Floor Area


75 %


90 %




Measurement: Regularly Occupied, Daylit Floor Area


75 %


90 %


Figure 2. Revised Hierarchy of Points Possible


Greenbuild International Conference and Expo 2013



Daylighting Guide for Commerical Offices - Part 2

Window Covering Design

Window covering is another important aspect when designing for daylight spaces.  Spaces must be designed to block glare, allow the view, and achieve energy savings at the same time.  Exterior shading devices are the best option to keep the space cool because they block the heat gain before it enters the space.


To block glare, select a window covering that is opaque enough to block the sun, such as fabric window covering that has 3% or less openness.  Horizontal blinds could also be used but tend to block more of the view than fabric shades.


Manually operated systems can be effective if properly used.  Since they rely on constant user attention to maintain glare control, these systems are usually installed in private offices or in “worst-case” scenarios.   This typically results in poor daylight performance and elimination of views throughout much of the year.


Automated glare control has the advantage of being deployed only when needed and retracting without the user intervening.  This creates greater energy savings when coupled with daylight controls while also allowing for longer periods of unobstructed views to the exterior.



TIP for Shading and Exposure

Northern Exposure – Shading typically isn’t needed with the exception of buildings angled to the east or west which may require shading on the north side in the early morning or late afternoon.

Southern Exposure – Less variable sun angles, making it easier to design shading systems.  Good access to strong illumination.

Eastern/Western Exposure – Shading design is difficult but critical for occupant comfort.


Influence of Furniture

Workstations must be kept low (42” or less) and directed parallel to the daylight source to ensure the views to the exterior.  Where higher panels (48” or greater) are needed or desired for privacy, they should be oriented perpendicular to the perimeter glazing.  Creating this workstation orientation allows for the most efficient use of natural daylight.

Workstations should be designed so that the occupant’s task view is parallel to the perimeter glazing, meaning that the daylight is coming from either side of the occupants view instead of straight ahead or behind.  This helps lessen the contrast between the task view plane (dark) and the daylight penetrating the glazing (bright).  This also helps prevent the shadow of the view from falling on the task view plane.


Interior Surface Finishes

When choosing interior finishes, the walls are another important surface to remember.  The “back wall” (wall opposite of the glazing) of a space is crucial to the perception of the space, since it is the furthest from the glazing and attains the smallest amount of daylight.  If this wall is brighter in appearance (higher reflectance value,) it will help balance out the bright glazing wall.  Having a lower contrast between the glazing wall and the back wall will give the perception of a larger space.  With this perception, occupants will be less likely to turn on the electric lighting.

            This effect can be done with the remaining walls and ceiling to make the space appear brighter.  However, the larger the space, the more difficult this effect becomes due to the inherent initial contrast.


Electric Lighting and Control Integration

Different Types of Controls

Photocell Controls: Automatically adjusts the light output based on detected illuminance.  This can be configured as step lighting (on/off) or be configured with a dimming capability.

Occupancy Sensors:  Turn lights on and off by detecting motion within the space.

Vacancy Sensor:  Requires user to manually turn on lights, but will automatically turn lights off after a pre-set duration.


A good rule of thumb for control systems is to place occupancy sensors in spaces with low occupancy numbers, such as private offices and bathrooms.  Spaces with low occupancy numbers (private offices being the best example) also utilize vacancy sensors.  Daylight sensors, or photocell controls, work best in spaces with large occupancy numbers.  This is due to the way the control works by automatically adjusting the electric lighting to coincide with the daylight addition.  This creates an environment that is self-efficient and is not dependent on the occupants of the space.  


Guidelines for specific spaces are as follows:

Open Office Areas: Where daylight is present, utilize daylighting controls.

Workstations: Utilize occupancy sensor controlled plug strips to control plug loads.

Restroom/Copy/Storage:  Install occupancy sensor controlled lighting.

Private Offices/Conference Room/Break Rooms: Install vacancy sensor controlled lighting.


Organizing Lighting Controls

            A daylight “control zone” is a group of fixtures in locations of similar daylight availability that are controlled together via a photocell to reduce light output when daylight is present, thus reducing the energy consumption.

            Automated lighting controls should be prioritized to areas where daylight contribution is expected to be high over time and where individual occupant control of lighting is not realistic, such as open office areas or lobby areas.

To read the full article, click here.


Daylighting Guide for Commercial Offices - Part 1

Benefits of Daylit Offices

Providing a daylit space creates a healthier and higher quality interior environment.  Increased individual productivity and human comfort is also found with daylit spaces.  Natural daylight allows for mental and visual stimulation necessary for proper regulation of human brain chemistry.  In addition to health benefits, allowing daylight to enter the space shows substantial energy savings throughout the building.

Design Inquiries for Designing Daylit Offices

Before you begin the spatial programming of the building, a few items should be in the forefront of your mind when deciding.  These inquiries include interior surface design and selection, shading for glare control, and shading for thermal comfort and heat gain control.  Interior surface selection has the opportunity to increase the daylight appearance dramatically, while shading control allows the building to effectively take advantage of natural daylight.

Best Practice Foot Candle Levels

Another thing to keep in mind when designing daylit spaces are the common lighting levels for different spaces.  The following footcandle levels describe the “best practice levels,” or in other words, the goals to achieve as opposed to the average level attained. 

            Reception Area:  5 fc   

           Working Spaces for Simple Visual Tasks:  10 fc

            Performance of Visual Tasks of High Contrast and Large Size:  30 fc

            Performance of Visual Tasks of High Contrast and Small Size or Visual Tasks of Low Contrast and Large Size:  50 fc

            Performance of Visual Tasks of Low Contrast and Small Size:  100 fc

Programming Criteria

When spatially programming the space, ask the following of each space:  Is daylight important for this space?  Are views to the exterior important?  How frequently is this space used?  What time of the day and time of the year will the space be occupied?

An example spatial programming might include the following:  Open Office Space – Daylight and view desired, occupants have individual glare control.  Private Office Space – Daylight and view desired, occupants have individual glare control.  Support Spaces – Minimal daylight or view opportunities required.  Building Core Spaces – No daylight or view opportunities are necessary.

After you have specified the spaces that desire daylight, ask the following of each of the daylight spaces:  What are the minimum daylight requirements?  How crucial is direct sun control?  What is the minimum footcandle level for the task that is performed in this space?  What might be the ideal solar orientation?  What might be the best strategy for providing daylight?  Side lighting?  Top lighting?  Are there maximum light levels required?

TIP for Programming Spaces  

“Daylight and view are typically preferred in areas that are most heavily occupied for extended periods of time, such as open office areas.  Corridors, circulation paths, break areas, copy/print zones or other short term gathering spaces may be tolerate of direct sunlight whereas fixed workstations or reception desks will almost never remain comfortable with the presence of direct sun.”

Space Planning

It is well known that open offices are typically occupied for almost the entire work day, while private offices are only occupied one-third of the time.  Also, since open office layouts are communal spaces, the shading blinds are not adjusted frequently.  This differs from private offices where the ownership is clearly defined, and the blinds are adjusted frequently.  The following values are the recommended distances from the glazing (illumination source) needed to provide adequate daylight and views to all spaces in need.

Locate open office areas within 18-20 feet of the perimeter zone (glazing wall) and at areas where direct sun penetration is limited (North) or less varied (South).

Position individual offices where low direct sun may otherwise be problematic (East and West), while allowing for individual control within the space with manual shading devices.

Top Lighting Strategies

Studies show that top lighting provides the most effective daylight into the building.  Designing them to be a diffuse light source easily takes care of any glare potential.  Compared to side lighting, top lighting covers a much larger area of the space.

Stay alert for part 2, discussing window coverings, shading and exposure tips, furniture influence, and daylighting controls.  For read the full article, click here.


Refining the Southern Window

Breaking down a southern window into components helps to design efficient windows.  These components can be arranged in multiple ways, to design a specific design detailed to the project. 

1.  The Daylight Window and the View Window

The Daylight window’s primary function is to provide a maximum amount of daylight deep into the space from the perimeter.  This window is located above the View Window, or generally above 7’-8’.  Glazing specifications are recommended to be a window glass with a high visible transmission value (Tvis 70% or higher), to allow the most light through the window.  Also, a low solar heat gain coefficient (SHGC .38 or less).

The View window’s primary function is to provide a view to the exterior from the interior.  This window is generally located within the view frame of the occupants, 3.5’ sill height and 6’-7’ head height.  This gives the occupants a view to relax their eyes, reducing eyestrain, while also giving a connection to the outdoor environment.  The glazing specifications for this window are generally tinted to a transmission value of 50%.  This reduction in light transmission reduces the contrast between the brighter window and the darker interior wall surfaces.

2.  Shade the View Window to Block Direct Sun, Eliminate Glare, and Reduce Solar Gain.

An exterior overhang that is about as deep as the window is high (1:1 ratio) will shade a south facing window during the summer months, which will dramatically reduce solar heat gain into the interior. 

In building types such as schools and offices, where the occupant hours are limited to the mornings through early afternoons (until 3 pm), this strategy can be used on the West Elevations.  By the time the sun comes around to the west side, with the sun altitude low enough, the building will be unoccupied.  Heat gain incurred after this time can be night flushed and the space will be cool by the next morning.

3.  Use an Interior Light Shelf to Provide Diffuse Daylight

Interior light shelves provide three major benefits, they block direct sun from penetrating the space through the upper daylight window, they reduce light levels at the perimeter, and they reflect diffuse daylight onto the ceiling plane.  All these benefits together combine to give the space a more diffuse, uniform lighting level.  Illuminating the surfaces such as the walls and ceiling plane makes the space look larger and brighter than it is actually.

A bright white or translucent, matte finish surface is recommended to provide the best light diffusing quality.  This material specification will have less contrast with the bright exterior also.

4.  Provide Adjustable Louver Blinds at the Upper Daylight Window

Interior louver blinds in the upper daylight window can provide direct sun control without significantly reducing the amount of diffuse daylight into the space.  They can be adjusted seasonally or when low sun angles penetrate the space.  They can be specified as mechanical units or manual.

5.  Use a Roll-Down Shade to Control Direct Sun in the View Window

An interior roll-down shade can control direct sun in the view window without significantly reducing the view to the exterior.  It is recommended to use a dark colored surface on the interior of the shade fabric.  This allows for a comfortable view through the fabric, while allowing room darkening capabilities.  Many newer fabrics provide a dark interior surface while maintaining a light exterior surface.  The bright light exterior surface helps reduce heat gain into the space. 

For more information and to read the full article with diagrams, click here.


10 Steps to Improving Your Lighting

Developing a single strategy or equation for lighting design is difficult due to the unique specifics of each project.  Following is a list of ten simple steps to improve any lighting design.

  1. Switch from cool and warm white lamps to Rare Earth (RE).  Rare Earth lamps give better color quality and produce more light.
  2. Switch from magnetic ballasts to electronic.  Electronic ballasts help eliminate flicker and hum, which are very common user complaints.
  3. Put more light on ceilings and walls.  Brighter walls and ceilings make the space appear larger and uniform brightness can reduce glare problems, which lead to user eyestrain.
  4. Add paint to your lighting tools.  Lighter color values improve the reflectance of the wall surface, improve the efficiency of your lighting design, and make spaces brighter.
  5. Include daylight in your lighting design.  Daylight has many benefits, including better color than electric lighting, a connection to seasonal rhythms, and increased occupant health.
  6. Illuminate architectural details and artwork.  This technique gives users a sense of depth, shadow, and contrast for visual variety, which is needed for the eye to stay interested and awake.
  7. Determine who will use the space.  The age of the occupants changes the amount of light needed for seeing and the amount of glare that can be tolerated.
  8. Determine what the users will be seeing.  Visual tasks are the first step to defining when, where, and how the light should be distributed.
  9. Calculate the lighting performance of your designs.  Lighting software is easily available and manual hand calculations are not difficult to complete.  Good estimates of the lighting distribution in the space are critical in order to determine an adequate lighting design.
  10. Know when to hire a lighting professional – and do so.  Good lighting designers offer a range of solutions, knowledge of equipment, creative applications, and comprehensive project management.

For the complete list, click here.  And for more information on specific questions or projects, please contact us at the IDL_Bozeman.