Daylighting Beyond LEED Part 1

I've recently submitted a Credit Interpretation Request to the USGBC from which I hope they will clear up some ambiguous requirements with credit EQ 8.1 - Daylight & Views - Option 2. To assist I've attached some images that help visualize the different sky conditions primarily used by daylight simulation tools. It will also help to have your LEED NC 2.2 reference manual with you as you read through the CIR.


"LEED reference material does not give clear guidance on how to use analysis software for documentation, and we are simply asking for general clarification regarding technical requirements. The numbers below correspond to the analysis steps in the reference manual.
From EQ 8.1 Option 2—Daylight Simulation Model:

1. Regarding materials, a problem comes up when we have a core and shell project where the reflectance values of internal materials are unknown. Could there be suggested default values to use in this instance?

2. The analysis grid 30” off of the ground is reasonable but the reference manual does not describe placing an actual work plane in the analysis model. Without an actual work plane there can be instances where a floor-to-ceiling glazing allows light to bounce further into back than if the spaces were filled with furniture or desks. A recently published book on the subject states “Since Option 2 LEED-NC Version 2.2 requires 25 foot-candles of daylight in 75% of regularly occupied areas at the workplane level…the simulation models should have the workplanes incorporated…” The image in this book shows a modeled workplane in the middle of the space with the caption “A model used for qualifying for the LEED daylighting credit.” Nowhere in LEED literature have I found an indication that we should model the plane, though doing so will affect the results.

3. “Clear sky conditions at 12:00 noon on the equinox (March 21/September 21)” is thought not to be technical enough by many experts. Perhaps LEED should cite using CIE Clear Sky as one option, or the Perez All-Weather Sky Model as another option, but with either it needs to specify how the location is defined:

• If we use a CIE Clear Sky (static simulation) option we must find “design sky illuminance” values. There are many ways to find this value but we should have a clear indication of an accepted source(s).


• If we use the Perez Model (static simulation) we incorporate actual weather data and our calculations are potentially more accurate. But with a static simulation we only calculate for 1 specific day and that day could be cloudy, so how could we approach this credit if we want our results based on weather data? Do we want our results based on weather data?
  It’s our opinion that analysis tools are sophisticated enough that LEED should require dynamic simulations which calculate annual daylight autonomy values from weather data.

4. Item 4 proves misleading when you get to 5.

5. This allows us to include the percentage of the floor area above the threshold even if the entire room is not above, contrary to item 4. This misunderstanding has generated multiple CIRs already, none of which explain it clearly. Am I right to assume that all area above the threshold can be counted, as long as we define these areas separately? Option 3 is more clear about this issue.

Item 5 also brings up a question of how to calculate the floor area from a grid of points. Some software programs do this for you but only after interpolating the values between points using contour lines. It should be explained how to derive compliant area based on point readings, and perhaps we should be warned that points falling within walls or columns will read “0” which throws off the data (your example image, Figure 2 on page 384 of LEED-NC 2.2 shows a reading of “0” for a point falls inside a column). Option 3—Daylight Measurement is also unclear about how to translate points into area, could you please be more specific?"