Option 3 - Measurement

There is not specific time to take the measurements. However, to get the most out of the measurements it is suggested that the measurements be taken under clear sky conditions as close to noon as possible. All windows in all spaces being included in the calculations require some form glare control device such as roller shades. These need to be controlled either manually or automatically.

Todd on the Supplemental Daylight and Views Calculation Spreadsheet provided by USGBC, for Option 3 Measurement the "Glare Control Type" column is under "For spaces with illuminance levels above 500fc". For Option 2 Prescriptive the "Glare Control Type" column is under "For spaces with VLT x WFR > 0.18". In both options it looks like "Glare Control Type" information is only provided for spaces that have too much daylight and are too bright. Do we enter glare control for all spaces? I would think there would be some situations where glare control is not needed (small windows on the north side of the building or windows with a very low VLT eg: 0.4). Also, we cannot include spaces over 0.18 or 500fc so I do not understand what these columns are included for. Thanks, Rebecca

Rebecca, I'm currently trying to get clarification on this exact issue. I should have a solid answer within two weeks. The daylight calculator is not consistent with the Reference Guide or the addenda from 5/09/11. Nowhere in any of the requirements does is state that "automated shades are required for spaces above the limits in all three options. This is what i have been trying to get consistent. If you scroll over the the box it states " View preserving automated shares are required for regularly occupied spaces with daylight illuminance values above 500fc". It says automated, it says required. So based on that and how it is noted, you would have to provide automated shades. Automated, not manual. Now what i have not confirmed yet is whether the average illuminance has to be over 500fc or whether just some calc points over 500fc would require shades to be installed. This is unclear and needs to be specific. This is one of my questions. If its just one point then you will need to install in almost all spaces. Spaces on the west, south , and east facades, even with exterior shading will always have a point or two over 500fc because of using both 9am and 3pm. Measurement option not likely. With the prescriptive path, well, if your over 0.18 you need automated shades. Now if you read the reference guide and the addenda, it states that glare control devices should be installed for high contrast scenarios. Well what type of glare, what level of glare, and what is considered high contrast? Do i reference IESNA and the definitions and contrast ratios? This is the issue i have, without specifically defining these values, one could argue whether or not shades are needed. What we do, and this is based on own work, is have some form of shade installed in all spaces. Glare comes in all forms, natural and unnatural. Even though your space may look norht, what about reflections from cars, buildings, and even off of snow. What would the occupants be able to do then. Even though a space is facing north, and depending on the atmosphere condition, could cause discomfort. Occupant, every occupant is different as to what they believe is comfortable viewing. So by providing shades in all spaces, you cover all scenarios and occupant needs. As far as to what to do with the shades as far as documentation, i say that the reference guide and addendas override any credit form or calculator. The credit form and calculator are just tools to help document. Hope this helps.

Rebecca, From my experience, you only have to include glare control devices for spaces that surpass the 0.18 threshold. You can include these spaces as long as you have automated view-preserving shades. In the columns for glare control devices you would just write the type of shades and select "yes" for the view-preserving shades column. Todd, I think only the spaces that go beyond 500fc have to have the shades, not every space based on an average. Is this what you're asking?

Lauren, The issue is that the calculator is not clear on the issue as whether its based on an average of each space or whether its based on either individual calculation or measurement points. Its not clear. So if i have a space using simulations, and i have some area in the space that has over 500 fc, do i need shades, or does the overall average. Its all a little fuzzy with room for assumptions, which should not be. It needs to be clearly defined to be consistent.

Rebecca, I don't enter anything in the Glare Control Type or the "View Preserving Automated Shades?" question columns unless I have a space that reaches the upper thresholds (0.180 or 500 at any point in the space). It is assumed that if your calculations come in below these numbers that you don't have glare (a very bad assumption, but that is the way the credit is written.) You will notice that only an answer of Yes to the "View Preserving Automated Shades?" question transfers the sf that you have entered that is over the thresholds under "Floor Area with Daylight Illuminance Levels Above 500 fc (sf)" to the column "Total Daylighted Area, Measurement (sf)." This means that you CAN include this space in your daylighted area if you have these shades and you cannot if you don't. This is also written directly into the credit. I agree the wording of the credit needs clarification, that most everything trumps the spreadsheet tool, and that there needs to be greater consistency between them. I don't see anything that would suggest an average value to me. The spreadsheet has two clear columns asking for floor area between 10-500 or over 500. I guess the words "for spaces with illuminance levels above 500" could be confusing, but because the Yes and No under "View Preserving Automated Shades?" act only on the "floor area above 500" column, this cannot mean average.

The words assume and assumption appear quite often in this discussion. When we are assuming one thing, and USGBC is assuming another, the outcome is only good if the assumption is the same. The issue is that no one should have to assume anything and this issue can be easily addressed. The original version of the calculator was quite clear, when they revised it in June 12, it got fuzzy.

Todd, Lauren and Jill, Thank you for your timely responses and discussion on the topic. We do not have any automated shades, we only have interior manual shades and fixed exterior sunshades for glare control. What I understand from the discussion is if none of our spaces are over 0.18 or 500fc we do not have to complete the "Glare Control Type" column. Todd when I scroll over the box on the spreadsheet I do not get message "View preserving automated shares are required for regularly occupied spaces with daylight luminance values above 500fc". As Jill points out SF over 0.18 and 500fc is included as daylighted area if you check yes to view preserving automated shades, but it is not included if you provide a description for glare control type (eg; exterior fixed sunshades) and check no or N/A to view preserving automated shades. The reference guide lists fixed exterior shading devices, exterior light shelves, interior light shelves, louvers, manual view preserving shades or operable draperies as common glare control devices. Does anyone know why the SF that utilizes these types of glare control does not count? By asking that question it occurred to me I should ask the next question, if you are pursuing the measurement option do you take measurements with the interior manual shades up or down? I had assumed you would measure with the shades up so the space would be the brightest. Thanks, Rebecca

I downloaded the latest version of the calculator in one of project that has just been recently registered. I get that note. Anyway, the reason you cannot include the square footage with the use of those glare control devices is because they are manual or fixed shading devices. Since you can;t trust the occupants to pull the blinds at a certain time, it doesn;t count. Measure with the blinds up. My whole issue is the wording which, with just clarification statements and some rewording would eliminate assumptions. When people are allowed to assume, there is no correct answer or the answer that is wanted is never obtained.

In addition to Tod's comment, the prescriptive method has many limitations. Does the exterior shading device help to reduce the glare? It is possible but the prescriptive method doesn't recognize that. My suggestion is if you have fixed shading devices, you can use simple sketchup modelling to assess whether there is direct light that penetrates to the rooms. If there is none, the simulation method can be used. If there is direct light, it is highly likely the rooms won't comply even we run the simulation. It is always recommended to bring a daylight expert in early design to assist the design process so he/she can provide design inputs and adjust the design. If it's too late in the design process, it is sometimes harder to make a justification because the architect and client will start questioning whether the point can be achieved without changing the design after they hire a daylight expert or run the simulations in the end of the design. If the intent is to provide a good daylight design and go beyond LEED, the luminance study and glare index calculation can be used during the design.