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What is It?

Daylighting means using direct sunlight to illuminate the interior of a building to meet occupant light requirements. This is accomplished by strategically placing windows, skylights and reflective surfaces in a way that maximizes the amount of sunlight that can be brought into a space in a controlled manner. Studies have shown that people are happier, healthier, and more productive when provided with ample natural light. Daylighting requires an effective balancing of potential (net) energy gains/losses, comparing losses in heating and cooling due to the lower R values of windows and skylights required for natural daylight, (compared to fully insulated walls and roofs), to the energy losses associated with powering electrical lighting necessary due to the lack of (day)light.

  • Also known as: sun lighting, natural lighting.

Why is it Important?

Daylighting is important to sustainability because it:

  • Reduces energy use from artificial lighting.
  • Reduces internal gains associated with the heat produced from electric lights.
  • When used in conjunction with properly designed and shaded thermal windows, does not add significant heat gain to a space.
  • Is proven to be directly correlated to higher productivity levels.
  • Is shown to result in healthier indoor environments when used properly.

When to Use It?

It is appropriate to use daylighting when:

  • The building has access to daylight. For example, if a building is heavily shaded by trees, or other buildings, the potential for daylighting would be greatly diminished.
  • Work tasks by the building occupants require very precise and/or very high lighting levels.

Green Garage Use of Daylighting

Sustainability Goals

The sustainability goals for the daylighting are:

  • Connect people with the natural this case the sun and outdoor plants. For example, when clouds move over the building, the interior will naturally become slightly darker, as one would expect.
  • Make sure that everyone inside has a view of the outdoors...again, to be connected.
  • Meet at least 80% of our lighting needs through natural daylighting.
  • Allow the net-Zero energy goals to be accomplished.
  • Respect and preserve the historic elements of the building.

Strategy and Conceptual Design

Daylighting Strategy
  • Only place light where it is needed. Supporting Christopher Alexander's - Tapestry of Light and Dark ([Lighting Requirements Pattern 135])recommendations (see the book A Pattern Language).
  • Meet the lighting requirements with natural lighting from two sources:
    • Windows at the perimeter of the building
    • Solatubes in the interior areas greater than 25 feet from the perimeter
Window Daylighting Design
Example Window Design for Daylighting - WWR = 20% / Height = 11ft

Our windows were intentionally designed to maximize the daylight they allow into the building while balancing the lower thermal properties of the windows versus the normal wall. All the original windows of the Green Garage were bricked/blocked in during the mid-1960's. In it's original historic condition, most of the interior light came from the windows, which were many and large, covering most of the perimeter of the historic building. We decided to place the new windows in these openings.

The window daylighting design:

  • The Window-to-Wall ratio (WWR) would be 27%. It was determined that this was the highest WWR possible for achieving a net-zero energy building and the lowest WWR possible if we were to achieve our daylighting goals of >80% of our lighting demand.
  • Bottom height of the windows (where they start) would be 4ft off the floor in the office and warehouse areas. This meets the general guidelines for desk height. It also is where the historic windows started and there is an existing window sill at this height.
  • Top height of the windows is 11 ft above the floor. This allows the light to reach approximately 27.5ft (2.5 x the height) into the building. This was about as high as we could go without coming into conflict with the wall-roof junction area. This area was already complex with the historic barrel roof design.
  • Visual Light Transmittance (VLT)- the glass is targeted to have a VLT of 0.50. A little higher (say 0.70) on the south side would be helpful if available.

Some of the daylighting design constraints:

  • No external shades/shelves can be placed on the south side, as the building is on the property line and they would extend over a public alley right of way.
  • There is a 45ft tall building 20 feet to the south of our building that shades the entire south side of our building from September to March.
  • The historic commission controls what can be placed on the outside of our building.

There is more information on windows available on our Sustainable Window Design page.

Solatube Daylighting Design
Solatube Photometrics - V3

We first examined skylights/roof monitors, but quickly concluded they had relatively low value because of the low light levels they generate versus the high thermal energy they created due to their low R values (R5), versus our roof design of R55. Additionally they added great design complexity to the barrel roof design, which was already quite complex. This was initially disappointing to dismiss the monitor skylights, as we planned on trying to replicate some of the historic monitors, but it was not to be.

So we then went with the Solatube idea and found that we could get our required light levels and minimize the thermal losses because the tubes require a smaller opening to produce the required light. Working with a local supplier, Gasser XXXX, we analyzed the space and developed a design using the Solatube product to meet our needs. It is shown in the diagram to the right. It includes 16 Solatube tubes that are 21" in diameter. They used the 330DS instead of the new 750DS. We'll need to do a final plan once the performance data is available for the 750DS. We assumed the R value = 5. We got this from an EPA report - this was not for the new 750DS product.

There may be a need to place controls on several of the Solatube tubes to be able to block the light when a presentation is being done.

The SIP manufacturer indicated that they could cut the holes in the SIPs needed for the Solatubes during the manufacturing process.

Daylighting Footcandle Estimates

Daylighting Estimate (in fc)- Window + Solatube Light ... more>>

We combined the photometric modeling of the Solatubes with the daylighting estimates from the window design to crudely estimate the footcandle levels throughout the building. We call it the Daylighting Map. It is on a 5' x 5' grid. The perimeter of the building is dominated by the lighting levels from the windows while the interior is primarily from the Solatube photometric modeling. We measured the light levels in our current building and determined the light levels at one foot intervals away from the existing glass door to determine how the light falls off. We learned that it falls off quite quickly. So we did not assume much gain from the windows beyond the 2.5 times the height levels.

We used a spreadsheet model because it was simple, free, and allowed us to focus on the major daylighting issues. We believe that we will certainly need to do some refinement of this once the building is built and we experience the lighting levels.

Daylighting Footcandle Estimates Spreadsheet

Integration Design

Integrating daylighting with the other lighting components does require significant thought. Some of the controls will be manual (even behavioral) and some will be automated. The key integration areas are:

  • Roof integration required to put the tubes through the roof in the correct positions.
  • Placement of the electrical lighting on controls that turn them on when the indoor footcandle measurement drops below 10 fc. It could be by lighting zone - but at least by building. It could also be a step down approach that phases the artificial light in, versus an on-off approach.
  • There is also the possibility to physically integrate the electrical lighting with the Solatube product. There is work being done by Full Spectrum Solutions to integrate their induction lighting with Solatube tubes. So the Solatube tube would become the induction lighting fixture and the Solatube diffuser would become the lamp lens. It would have a control to bring on the artificial light when the natural light fell below a level.

Supporting Science

The detailed daylighting calculations are shown in pages included here. We thank Jamie Pachla for her great contributions to our understanding of how to work with daylighting through a better understanding of the interrelationship of our design with the lighting effects through her photometric modeling.

Proposed Materials / Suppliers

Development Story

The Daylighting - Development Story page contains many images and videos documenting the process used at the Green Garage to design, build and operate our daylighting conceptual design.

Related Internal Links


To Do's

  • Link to google spreadsheet
  • Jamie's data
  • Put the building elevations into the page
  • Resources
  • Short Video and image to top of page
  • Upload images onto Development Story page
  • Daylighting footcandle estimates spreadsheet link is incorrect in 2 places(I think - Peggy)

Peggy edited this page :)