Yes, views need to be through clear glass. Views through fritted or translucent glass is not acceptable since the view would be obscured.

If the owner is not providing them, then the requirement would fall to the tenant and have to be noted in the lease agreement to ensure the daylighting requirements are still met.

Just the area of the transparent glazing.

I have always done just the overall window rough-in dimensions.

"I have always done just the overall window rough-in dimensions." That means for me also opaque elements, which is in my opinion against the intent of the credit. But I can not find a official statement to this issue...

The reason you cannot find any official statement on this is because why would you take credit for opaque area which does not provide daylight to a space? You can say its against the intent of the credit. Is there anyway in which a reviewer could determine whether you are doing this or not?, No, unless you provide CAD files that can be measured.

Well if you are using the opaque elements of the window such as mullions and frames, then you should be reducing the VLT you are using because you are taking credit for an area which is not providing daylight to the space. Modeling protocol would be:

 the area of the sills, jambs, and mullions can be calculated and summed into an ‘occlusion area’. Then the net window area can be calculated and the ratio of the occluded area relative to the rough opening determined (occlusion area/gross window area = reduction factor). Then, the gross window area can be simulated with the reduction factor applied to the VLT of the specified glass. (E.G., If the gross window area or rough opening is equal to 100 square feet and the occlusion area is 5 square feet; a 5% reduction factor is applied to the VLT of the glass. Therefore glass with 70% VLT X 95% = 66.5% VLT.)
 When window framing details are not known, a 20% reduction factor should be assumed relative to the rough opening. For skylights, a 10% reduction factor should be assumed relative to the rough opening.

Would a typical mullion of like 1 inch make a difference, probably not, but larger frames of store fronts and curtain walls it would be.

Not to worry. No one is trying to "take credit for opaque area which does not provide daylight to a space."

If we can all agree that: 1. LEED is not the authority on daylighting, 2. the prescriptive method is intended as an easy, cheap way to determine credit compliance and not daylighting aptitude (an important distinction), and 3. the prescriptive method is crude, then I submit that it is not the intent of the prescriptive method that the design team spend their time calculating the area of every window pane, but that it is assumed by the creators of the prescriptive method that all windows have frames and mullions.

This forum is for LEED users. My statement is intended to help users use LEED. Reviewers have always had the option to review my calculations with drawings or to ask for more drawings to do so.

This is similar to the confusion over the simulation option and what it means to meet the minimum footcandle level at 3pm and 9pm. Even though it seems to me that the 75% should be met only with points that meet at both times, reviewers haven't been responding that way. It is all in the interpretation. I'm letting people know that reviewers have been responding to my interpretation that a certain amount of occlusion is already included in the prescriptive method.

I'm not sure where the 20% for windows or 10% for skylights comes from? Can you enlighten me?

I don;t worry whether people take credit or not. Much of the information provided must be accepted because we are all professionals who put our names on the results. Just like no one ever manipulates simulation parameters or other tweeks which cannot be asked for by the reviewer unless there is an unquestionable issue that has been submitted. It must be assumed that everyone is doing it the right way and are honest. There are a number of projects that have earned the daylight credit over the many versions that are very far from what many of us in the industry would consider well. if even daylit. But their case studies spout that their building is daylit and has earned the credit.

I agree with all you said, x4.

Reviewers don;t really have that option anymore of just calling out items that look questionable and asking for documentation that is not required. The days of credits being audited, just to be audited are in the past and to get documentation that is not required submitted needs to have pretty definitive case presented to get it.

Jill, the info i submitted is from a draft of a document that will probably be published here within a few months and has been the work of many daylight industry practitioners to create consistency across the board. I can;t specifically say how the 20 and 10% was established since i was not one of the contributors. But i'll try to find out.

There are no requirements as to when you should take the measurements. I would suggest that you take in under clear skies as close to solar noon as possible and near one of the equinoxes.

Under the Timeline Tab, Submittal Review, you will select credits which are complete for review. So to defer EQc8.1, do not select it to be submitted for review for the design review. When time to submit the construction review, select it for submission along with the other credit.

This also explained if you select help in the quick links when in the credit information tab.

You use the area in your daylight zone which is either determined by 2x the window height for the depth, or if there is an obstruction, i believe it is then a 63 degree angle. This is the area that is used in the calculations.

Cecillia,

See this guide by LEEDuser. http://www.leeduser.com/credit/NC-2009/IEQc8.1#doc-tab

And page 400 of this "Addendum Details". https://www.usgbc.org/ShowFile.aspx?DocumentID=9377

You use the floor area that makes the result come out between 0.150 and 0.180. If your initial result using the 140 sf comes out above 0.180, none of the area complies. If it comes out below 0.150, adjust the depth of your floor area down until the result is above 0.150. This is the area of the room that complies that you enter into the spreadsheet. You can break up the space how you like as long as each one is connected to a perimeter zone with a window.

Jill Dalglish wrote: "You use the floor area that makes the result come out between 0.150 and 0.180. If your initial result using the 140 sf comes out above 0.180, none of the area complies. If it comes out below 0.150, adjust the depth of your floor area down until the result is above 0.150."

Jill, just to clarify, are you saying that we are allowed to adjust 'bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. depth to core' as much as we want until we get a value between 0.15 and 0.18? Can you please clarify a bit if you don't mind, as this has not been my interpretation in the past - rather it has been that the depth is 2 x the wall height, or less based on a 63 deg angle if there is a dropped ceiling or other obstruction. This has always produced wildly different values for each zone, often out of the 0.15-0.18 range. As a result we have basically given up on the prescriptive path as it is far too rigid. If we have no control over the bay area or window area, we would basically need a different TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. for each zone, which is unrealistic. We have instead tried to learn Ecotect / Radiance to show compliance (which I think is more accurate / fun, but much more time consuming, and a big disappointment if you put in several hours of work just to see that you don't meet). In fact I have considered the rigidness of the prescriptive path is the US/CAGBCs way of saying "sure you can do it this way..but don't waste your time, it wont work unless you have a square box). If you are saying otherwise this may change a lot of our approach!

FYI, I am in Canada and using the LEED Canada Reference Guide, which is even more vague than the US version on this credit, proving to be very frustrating. As far as I can tell, our Ref Guide gives no indication to being able to adjust the bay area.

As much as I would rather be encouraging use of simulation instead because it is much more informative, I do understand that it is more costly than the prescriptive method.

So, the answer is Yes, and I finally found the link to the document again from LEED where I had originally seen it. Click here: https://www.usgbc.org/ShowFile.aspx?DocumentID=9377 then go to page 400. A little more than half way down the page, it says "If the result is between 0.150 and 0.180 the space counts as a daylight zone. If the result is between 0.000 and 0.150, a portion of the space is [compliant]. Calculate the [compliant] floor area as follows: Divide the calculated result by 0.150 and multiply by the floor area of the space. This fractional result represents the floor area to be counted as qualifying daylight area." This math is basically shrinking the area of the bayA bay is a component of a standard, rectilinear building design. It is the open area defined by a building element such as columns or a window. Typically, there are multiple identical bays in succession. to the point where it just meets 0.150.

There is no calculation solution for if you are over 0.180. You will need to modify your design to get it under the 0.180. And, I would say that if you are over the 0.180, you are *definitely* over-lighting with daylight and the project would benefit greatly from a re-design.

You still need to do the 63 degree calculation to determine your eligible head height.

What is your backing for saying that a space is definitely over-lighted when only using the prescriptive path? This is not to start any issues, (just a professional discussion) but since this method considers nothing in relation to climate, location, orientation, etc. and you have found a study or have yourself some examples that would make the number 0.180 a daylighting benchmark, i would like to know.

Jill,

Thanks a lot for the clarification ,that really hopes. Now to determine whether or not the CAGBC will accept this method.

We re-ran our prescriptive calcs for a MURB building using this method and are finding that the TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. which gives us the most compliant area is 0.31. This seems really low to me. In fact, I rarely see below 0.65 or so with a reasonable SC we like to see. Is this is a Tvis you would expect?

It seems to me that by allowing this method when you are below 0.15, and not when you are above 0.18, they are placing a real emphasis on glare reduction. I can't understand why glare is such an issue in these calculations, especially when they mandate glare control anyways. Anyone have any insight into this?

Todd, I am basing it on Cecilia's original question regarding a 140sf office with 0.7 TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing.. It is my professional opinion based on experience that in most climates, locations and orientations, this office does not NEED 36 sf of 0.7 VLT glazing for adequate daylight. In fact, I'm surprised that the original design with a 25 sf window doesn't comply. I can see an argument based on certain climates, locations, orientations, window and ceiling layouts where it might not be overlit. Again, the prescriptive method is a very poor method for evaluating daylighting, which I know you agree with. But, I do think that, just based on experience, if you achieve the 0.180 in the calculation, in most situations, you can do with reducing window size or VLT. Going the other direction is not as easy as I can see a lot of cases where a good daylighting design will come under the 0.150. What is your experience?

Ciaran, all of this information can be dug up from the usgbc.org web site. The link actually refers to the 5 May 11 addendum, not the full reference guide.

Adam, the glare control they require is for direct glare. I think what they are trying to accomplish with the restriction on going over the recommended VLT*WFRWindow-to-floor ratio (WFR) is the total area of the window (measured vertically from 30 inches above the finished floor to the top of the glass, multiplied by the width of the glass) divided by the floor area. is more of a "quantity" glare avoidance meaning that glare can come from high contrast but also purely high quantity of light. Here in Colorado, I only recommend VLT above about 40% for north facades, but I can see in Canada why you might want a higher corresponding SC value. I have seen VLT installed here at 18% facing south that almost looked too bright. It is all relative once you get inside the building and your eyes have adjusted to ambient levels (to a point.)

Thanks Jill,
I have found and have data from our own projects, both simulations and actual measurements, that many of the spaces would not earn the credit using the prescriptive path, yet are exemplary in simulations. We have gone back and done measurements in a few of our projects to verify our simulation methods and these spaces are meeting the requirements in overcast skies (measured) for about 50% of the space. Which was the design strategy in which we implemented.

Ciaran,
The prescriptive method is really meant for projects that are not truly integrating daylight into the design. You are correct that to meet it, you have to have these very low VLTs. Understand this prescriptive path is somewhat based on ASHRAEs' method of establishing the percentage window to wall ratio to reduce solar heat. (I believe it was ASHRAE) So a project not really considering the multiple factors of the impact of the sun on the building are somewhat forced into these low VLT type glazings.

Jill,
18% VLT and it was too bright? I know the air is thinner there, but that is like wearing sunglasses.

I did say "almost" too bright. Can you say that you've never had your sunglasses on and still had more than enough light? The view windows on this EnergySmart high school have a VLT of 18%. http://www.psd.k12.co.us/school/fossil-ridge-high-school

The windows on this fairly new high rise alternate between 20% and 8% (eight percent) VLT. When I was there and before I knew what the VLT's were, I guessed that the 8% glazing was 30%. http://www.xcelenergy.com/staticfiles/xe/Marketing/Files/CO-Bus-EDA-1800...

IT ALL DEPENDS ON HOW YOUR EYES ARE ADJUSTED. On an average day, if there are 5,000 fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. outside, 8% of that is 400 fc, right? Now, that is right inside the glass, but to look through it, it doesn't look dark.

Don't be afraid to lower your VLT and correspondingly your SHGCSolar heat gain coefficient (SHGC): The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. and save on cooling load. Prove it to yourself first by visiting buildings with low VLT and low SHGC.

Todd, what I was asking was, in your experience have you seen a space that was over the 0.180 by a prescriptive calc, and would be hurt lighting level-wise by cutting back on window area or lowering VLT?

Jill I have yet to use the prescriptive method in any of our projects so i cannot say that a space that is over 0.18 would be hurt by lowering the VLTs. I know many of our spaces would not meet the 0.15, yet are well daylit spaces from many aspects. So based on that i can see where a space over 0.18 would not be effected in providing adequate daylight by reducing one or both factors. Its worse to be over daylit then under daylit.

I;m not convinced on those very low VLT glazings. So you get a SHGCSolar heat gain coefficient (SHGC): The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of below 0.20 with such low VLT. I can use a VLT of between 60 and 70 and get a SHGC of between 0.25 and 0.30. In our experience and how we do things is that we bounce between the daylight sims and energy models on this matter to find the correct glazing that meets both the energy and daylight goals. What we have found is that once you get below a certain SHGC, the difference is negligible (weighing in other factors). The big difference is the savings from daylighting, and those low VLTs will not get you them. Everyone forgets about the frame and when you have a high performance glass in a cheap conductive frame you are not helping yourseld at all. There are so many variables and that is why cookie cutter buildings don;t work.

I have been in many buildings with these super low VLT glazings and i have yet to be in one where the lights where not on when the sun was out. Secondly the actual quality of view is dramatically decreased. Occupants in those spaces experience a dramatic difference between interior and exterior lighting levels. There have been studies on this and the next version of LEED is proposing a VLT lower limit to even earn the views credit.

I will say that is really dependent on the location and what the target daylight levels are. So if you are meeting what you targeted and have provided a good daylit environment for your occupants, then you have done the right thing.

A lower SHGCSolar heat gain coefficient (SHGC): The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. is only one reason for a using a lower VLT. The other is to not overpower the electric lighting design. It is very difficult to daylight most spaces 100% of the occupied hours. Therefore, you will be using some electric lighting to augment the daylighting. However, if you have 400 fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. on the wall next to the window and 100 fc on the wall away from the windows, the wall with 100 fc will appear dark and most occupants will want to turn on the lights in this situation. For this reason, lower VLT can result in higher daylight harvesting.

I'm not saying that low VLT's are appropriate in all cases. I'm just saying that they should be considered.

I'm not sure why you brought the frame into the conversation. Are you saying this affects the VLT somehow?

I have been in these buildings in many cases where the lights are off and the daylighting is nicely balanced across the space. I invite you to come out and experience them. Come up to the 20th floor of the Xcel Energy building and I will show you the beautiful view of the Rocky Mountains through the 8% and 20% VLT glazing. The view is not diminished.

I would like to read the studies you are referring to. Can you tell me where I can find them? Of course there is a dramatic difference between interior and exterior lighting, there usually is. What is the harm in this?

Thanks for the discussion! This is fun!

Jill I will glady take you up on coming out to Colorado to experience the scenery and the buildings so when i get the chance i shall.

I brought in the frames because it seems that when the discussion of energy and daylight is brought about they are not discussed as much as they should. It is all part of the system . So it was added topic in this great discussion.

I see, and agree about the contrast levels with the lower VLT used. An interesting concept in balancing out the daylight in spaces where daylight levels cannot be reached at the back of the space. So rather than overpower the occupant within 10 feet of the window wall just to meet 25 fcs near the back of the space. Use the electric light to make up the difference and provide all occupants a comfortable environment.

The Excel building has floor to ceiling glass, so the VLT is going to have to be lower, agree and see where you went this. Again, its about balancing all aspects together to achieve the goals set. I would not have recommended anything in high VLT range. My reference of 60-70 VLT would be for a project with an established sill height with a window to floor ratio of between 10-20% depending on the orientation. This would be to start.

Completely agree that you cannot daylight a space 100% of the time and meet all the other requirements without the aid of electric light. In fact daylight and electric light should work in harmony to achieve the required daylight and contrast levels.

I will dig up those reports that i have read on the quality of views and post them. I have also had discussion with others about the clarity of glass and the effects of visual quality. Its not that the view is obscured or blurred, it is the idea about the amount of light received by the eye and the reduction in the subtleties that occur with daylight as the sky changes and the sun moves. The basic idea is to provide a view to the exterior that is as close as it could be if you were outside. This relates to biophilia.

To be clear, I am not responsible for the Xcel Energy building but I have been in it with the glazing supplier.

Jill,
Two reports and a book,
A room wit a view: A review of the effects of windows on work and well being."

Heschong and Mahone" windows in office 2.6.10, page 120 in the results. However, you have to read alot of the report to come to the their conclusion on this.

Biophilic Design, Chapter 15, and the sections on windows.

There is one i read and of course i did not bookmark it or save it to our library, that really had some specifics on the effects of lower VLT glass and view.

One question with the Excel building, how is the view at night from the interior to the exterior? Sometimes, depending on the actually property of the glass, the reflections at night for one looking from the inside is terrible, its like looking in a mirror.

Thanks for the info.

A side note: "Xcel" is their misspelling, not mine.

I have not been in there at night. There is that potential.

I would not say that the prescriptive method is a means to calculate daylight. It is a method that is used to determined whether a space meets a certain set of criteria that would provide adequate levels of light. Its like the older glazing factorThe ratio of interior illuminance at a given point on a given plane (usually the work plane) to the exterior illuminance under known overcast sky conditions. LEED uses a simplified approach for its credit compliance calculations. The variables used to determine the daylight factor include the floor area, window area, window geometry, visible transmittance (Tvis) and window height. calculation where the area and property of the the space is used in a set formula to determine a number, nothing is based on any type of illuminance levels.

So if you are truly wanting to know the daylight levels of the space, simulations or actual measurements are the methods to use.

I would not use the prescriptive method if I designed a space which has exterior shading, light shelves, sloped ceilings, or any other implemented daylighting strategies. It, like you said, is just general.

If you have an open office space with just sidelighting, and or toplighting, and you just want to meet the credit requirement, then the precriptive method would be applicable.

I believe the prescriptive path would be what you want to follow to help you determine compliance if you don;t want to go with simulation.You would be using the daylight zone, which would be the depth from the window wall, twice the window height, or at a 63 degree angle.

From what you are saying, I'm assuming perimeter offices about 10 feet in depth, then a corridor with more interior offices. The prescriptive path will not work in shared daylighting scenarios, so only the offices along the perimeter can be looked at. If thats the case, you would probably need a bilateral daylighting scenario, which would be toplighting and sidelighting. Areas under skylights can be analyzed using the prescriptive path.

There are simulation programs which do not have such a large learning curve as those you have mentioned. SPOT is one which can do simply geometries. Not sure what other programs you are using or have. If you have AutoCadd, there is 3D Studio Max or Ecotect. The learning curve is not as large (my opinon) as others.

Since this project is in the earliest stage of design, i would use this opportunity to look at the daylight, not to earn a LEED credit, but to provide the best daylighting scenarios to the occupants and for energy savings. This requires more work in the design phase, and to be done correctly you really need to use simulation.

Hi Todd,

Thanks for the reply. In actuality we have 25' of open offices around the perimeter, 5' corridor, then 12' deep offices (glazed towards the open office to allow for "borrowed" light to come through) With this layout, between the perimeter glass to the back wall of the offices is 45' or so. the core itself contains a meeting room and there are a lot of offices which do not have daylight from perimeter windows because they are located in the core. I think your opinion is dead on, having skylighting would definitely benefit in terms of health and well being standpoint.

I'll take a look at SPOT for quick analysis. We've been getting a lot of assessment related issues early on in the process to decide on what space is viable for LEED and daylighting. I guess this will be worth the investment in time to learn something quick.

If there are any other suggestions I'd be pleased to hear it.

Cheers,
D

Just an update. I tried sketchup and Daysim and it seems to be working out except intuitively I should be getting light into the offices (fully glazed wall oriented towards where the daylight is coming through) and the readings in the offices are 0. has anyone got a method to deal with this? i made a wall in sketchup and added a default single pane glass on it but no reading of light coming through, it's acting as though it's a solid wall.

any ideas would be greatly appreciated.

Thanks,
D.

Not knowing the location or climate of the project, clerestories are something you may also consider. Depending on the ceiling height and the size of the skylight, it may cause glare issues (over daylit) in individual offices because of the skylights orientation to the sky dome and climate. Clerestories can help reduce this issue because of the geometry. Roof monitors can also be implemented and orientation needs to be considered to reduce the effects of direct solar penetration. Another option may be solar tubes. they are smaller than skylights and can provide a effective level of illuminance in individual offices or small conference rooms. But simulation or measurements would be needed to demonstrate LEED requirements.

Are you using the Daysim materials file for sketchup?

Yes, i'm using the Daysim materials provided by the Daysim skethcup plugin. i tried a basic model, it was okay, now im implementing rooms and with full height glass and it's not working.

Denise, i cannot accurately say what is wrong with your model without looking at it. I don;t typically use Sketchup to Daysim and have only really just used Daysim that way a few times. I usually go from Ecotect to Daysim. Here is the link to the Daysim forum that may help answer your specific question.

http://groups.google.com/group/daysim

Thanks Todd. I'll look into it. I should probably try Ecotect since we have it in the office. :)

Cheers.
D.

One piece of advice with using Ecotect and Daysim, keep your file names short and your paths to those files as short as possible to reduce any errors. I highly recommend reading the Daysim Tutorial on how to export from Ecotect to Daysim.

Hi Denise,
A good rule of thumb for daylighting and the LEED daylighting credit is that usable daylighting reaches back into a space about 1.5 - 2 times the head height of the window. In your case about 1.5 x 12' or 18' around the glazed perimeter. As you can see with your very wide floorplate, reaching the LEED credit is not really attainable with just the windows. (120' + 120' + (120'-(18'x2))) x 18' = 5832 sf or 41% of your total space of 14,400. Even subtracting out the non-regularly occupied space isn't likely to get you to the 75% required.

To address what you asked about the depth in the LEED 2009 CI reference guide on pages 58 and 59 they allude to a recommended depth as Todd and I are saying of 2 x the window head height. I agree, it does not address the issue very well.

One method is to use the downloadable Supplemental Daylight and Views Calculations spreadsheet. The other option is to just create your own, which i prefer because the downloadable one sometimes has issues.

Just include the space name and number, total regularly occupied space, compliant space at 9am, compliant space at 3pm, total compliant space. I also include the file name of the results that are uploaded for that space. Final calculations at the bottom.

Look in the Reference guide for LEEDv 2009 in EQc 8.1 and there is an example calculation result.

Jos,

Recently the Supplemental Daylight and Views Calculations spreadsheet has been updated and is much more robust now. I find it works well. It is available under credit information -- credit resources in LEED-Online. The latest version of this spreadsheet is only available if you are using the latest version of the form as well (generally v03 or higher) and it can be used for IEQc8.2 too, which means fewer uploads and more consistency.

I downloaded the spreadsheet form credit resources but it says 10 fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. instead of 25. Additionally it only has space for one case (9 am or 3 pm). It is a bit confusing. Any thoughts will be appreciated?

An Addendum from last year changed the minimum illuminance level from 25fc to 10fc. Not sure what version of the calculator you have, but with the one column, it would be the the square footage that is compliant at both 9am and 3pm, which would be lesser value at the respectable times.

The area of and close surrounding area of the reception desk must be included. The rest of the lobby can be excluded. All circulation areas, such as corridors and hallways can be excluded.

Can either of you help me out with understanding the 10% area exclusion option mentioned?

Jill did some digging on the templates and PIF forms and could not find a 10% exclusion option.

Robin,
What time of day did you take the measurements? I'm assuming they were done recently, in Oct or Nov? What is the transmission of your glazing? Do you have any shades or other glare protection and are they in place when you are doing the measurements? You need to have your glare mechanisms in place when you do your measurements. Are they automated? If you're shades are automated, you are excluded from having to be under the maximum. Are you taking the measurements in direct sun?

Your measurements are not outside of the normal range of direct sunlight. The swing is normal too.

For my own interest, do you feel there is too much daylighting and/or do you feel there is glare? I say "feel" because these things can be somewhat subjective. Your eyes might give you a different feeling from your light meter and your neighbor.

This is a good example of why the credit requires daylight to have glare control and be within a range of footcandles (min AND max.) Glare and over-lighting are the two main enemies of good daylighting. As you are over the max. fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. limit, it is unlikely you'll be able to swing the review team. What type of activities occur in the building? The only thing I can see that might convince them is if the activities require the amount of light you're getting per the IESNA Handbook. Which, in my recollection, is detailed surgery or hand drafting!

Close the blinds and retake the measurements early or late in the day (since this version of LEED doesn't prescribe a date or time to take measurements).

Let us know how it goes!

Hi Jill,

Thanks so much for your reply. The reference guide doesn't say that the glare control needs to be down when the measurements are taken so I had originally taken them will all of the blinds (manual and mechanized) up. I took the readings on September 7th from 11:30 - 1:30. There are blinds on every window, manual in open office areas for occupant control and mechanized on windows above head height and at the clerestories. Not sure what the TvisVisible light transmittance (VLT) (Tvis) is the ratio of total transmitted light to total incident light (i.e., the amount of visible spectrum, 380–780 nanometers of light passing through a glazing surface divided by the amount of light striking the glazing surface). The higher the Tvis value, the more incident light passes through the glazing. is for the existing glazing- it's definitely not clear. I will take the readings again with blinds down - ugh!!

The users are computer programmers and they keep the blinds down all the time. Amazingly, the space doesn't feel overlit even with the shades up. It feels really great. It was bewildering taking the readings and having them be so high because it feels nice in the space - not like your standing on the surface of the sun! :)

We have had zero complaints from what is a very sensitive user group with regard to light levels and glare. This tenant is very attuned to their employees comfort and have already sent out surveys soliciting this kind of feedback from them. Everyone LOVES the daylighting. No complaints about glare or light levels.

Our lighting power reduction, including the task lights is 46% below ASHRAE. I know they are saving more than that becasue the lights are only on for an hour in the morning and a couple of hours at the end of the day (especially this time of year). Great success story for daylighting - hopefully the second round of measurements will reflect this!

Any thoughts on an acceptable fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. range I should look for with the blinds down?

Thanks again for your help!!!
Robin

You're right, it doesn't say if the blinds should be down or up. This to me means it is your choice. Glad to hear this level is acceptable and there are no glare problems. The only other thing I would double check is that your meter is on fc1. A footcandle (fc) is a measure of light falling on a given surface. One footcandle is defined as the quantity of light falling on a 1-square-foot area from a 1 candela light source at a distance of 1 foot (which equals 1 lumen per square foot). Footcandles can be measured both horizontally and vertically by a footcandle meter or light meter. 2. The non-metric measurement of lumens per square foot, one footcandle is the amount of light that is received one foot from a light source called a candela, which is based on the light output of a standardized candle. A common range for interior lighting is 10 to 100 footcandles, while exterior daytime levels can range from 100 to over 10,000 footcandles. Footcandles decrease with distance from the light source. The metric equivalent of a foot candle is 10.76 lux, or lumens per square meter. and not luxMeasurement of lumens per square meter.. I can't say what to expect for the blinds down because I don't know the transmittance of the blinds - hopefully below the 500 fc. Great job on the lighting power density. Good luck!

People will be more acceptable to higher daylight levels then electric lighting levels. So 50fc of electric lighting on a surface may seem glary or even too much, but daylight levels of 50 or even 100 are perceived differently and are more accepted. We are animals, therefore natural occurrences are accepted by us.

Two stories worth of glazing along with a bilateral lighting condition is the reason for such high illuminance levels. Typically one would not have that much glazing for computer use. I would look at levels with the blinds half down to be similar to single story glazing.

The reality with LEED is that not every project can earn every credit nor can every credit be tailored to meet every type of project or condition.

Hi Michael,

This credit focuses on "regularly occupied spacesRegularly occupied spaces are areas where one or more individuals normally spend time (more than one hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building.." So, you would not include the area of the walls... unless they are movable and some of the time may be occupied area?

Your not missing anything, what you are getting is the frustration with the prescriptive method. It is a formula, that does not consider climate, site orientation, interior reflectances, etc. It is meant to be used by projects, and you are correct, to reduce over or under daylighting space. Projects that ignore all apsects of daylight and create glass boxes will have a hard time meeting the prescriptive path. We have projects that meet LEED requirements through simulation, and actual measurements that would not have earned the credit using the prescriptive path. If we would have designed the space to meet the prescriptive path requirements, it would actualy be under daylit. North facing spaces in cloudy climates require more glazing and higher VLTs. If you truly want to daylight a space, then simulations or models is the best option.

Have you tried multiple zones in a space

What do you mean by there will be a problem with the sensor file? You can either create a sensor file using a text editor manually based on what you want your sensor coordinates to be or the SketchUp plugin su2ds will automatically create one for you based on the plane and spacing you define. See http://code.google.com/p/su2ds/

I want to say Daysim is your best bet but Sept 21 9am and 3pm may or may not be clear sky conditions (as the credit vaguely requires) depending on the weather conditions in the weather file. Directly in Radiance you can define the sky condition you want. IES-VE might be a good candidate.

Thanks Ramana. I now have the Sketchup plugin that will allow me to automatically create the text file.

I'll look into Radiance and IES-VE.

You're welcome Susan. AGI 32 is another tool that comes to mind.

Exporting to Daysim will give you Daylight Autonomy, which is based upon a year's worth of sky data for a location. The requirement is for a specific time and time condition, which Daysim does not create.

I would export your model into Ecotec, and then export to Radiance. Ecotec automatically creates the sensor file which is then used in Radiance and Daysim. You will be able to specify date, time, and sky condition in Radiance. However, your units will be in luxMeasurement of lumens per square meter., so you will need to revise the input lux data, which you write a simple formula in the calculation grid import table. This will convert your lux to footcandles. You could also leave it in lux and explain the levels to the reviewer.

Susan, as you can see, daylight modeling is nearly as complicated as energy modeling. Do you hire out for energy modeling? I would recommend the same for daylight modeling. Once you figure out all that is listed here, you still need experience to help you understand the results. Why spend your time and money on training and software when it is a small, specialized portion of your project? Plus, you will develop relationships with these experts who are also experts in glazing and lighting.

At first glance, it sounds like your meeting rooms, private offices, and open office areas would be regularly occupied spacesRegularly occupied spaces are areas where one or more individuals normally spend time (more than one hour per person per day on average) seated or standing as they work, study, or perform other focused activities inside a building.. If the kitchenettes, lounges, and printing rooms are not places where people stand or sit to do work, they are typically excluded. Print/ copy rooms where people go to pick up prints and office supplies would not usually be considered "regularly occupied" whereas a high-volume printing room where people operate the machines as part of their job probably would be considered occupied.

For the open office areas, I think it's most common to include the circulation areas in and among the workstations, but exclude the main circulation area closest to the core.

You may get different results with a daylight simulation or by taking measurements with a light meter - the prescriptive method is a pretty rough approximation of actual performance and the least accurate.