Option 3 - Variable conditions

Option three only has the minimum requirement and with lower sun angles at this time of year you should not even have any issues on even partly cloudy days, dependent on your VLT of the glazing.

I don;t believe taking measurements to determine the daylight levels of your building is a waste of time, whether its for a credit or not. The information can help in making future decisions on energy saving strategies or address occupant issues.

Being that there are no specific requirements as to when the measurements have to occur, and even if they have to occur on the same day, i would take them.

I agree that you should continue with taking measurements but I disagree that lower sun angles aren't going to cause issues.

Summer sun IS brighter, generally than winter sun. For example, here in Denver we get an average of 1.5 times the lumens from the sun at noon in June than in December. The farther north you go, the greater discrepancy there is going to be from summer to winter.

I say wait until a nice sunny day in June and try for the credit again, if you have the time to wait! Good luck and if you remember, come back here and let us know how it went!

One more thing, you can look up the difference in your location's summer and winter lumen values through weather files. One easy way to access these are from Solatube. They publish these for use with their IES files. You don't need the IES files to see the difference, just letting you know why they have them.

I stand corrected, based on the most recent addenda, you must meet at least 10fc and no more than 500 fc, So depending on when this was registered and if the addenda is applicable, then low winter sun angles may be a problem depending on the time. If the addenda is applicable to your project then the minimum will help you.

Sorry, they don't have them available online. They like to give them out personally so that they can explain how their IES files work. If you don't have a local rep, I'll bet you could just call them directly.

I could probably dig up a weather file for you when I clear a few things off my desk. Where is your project located and do you happen to know its nearest airport?

Hi Maura,
Just my 2 cents, if I were you, I would just try to measure the daylight. I don't think you need to spend a lot of time to ensure the credit achievement if you can strategize measurement correctly. You can take some measurements in certain rooms that may represent the floor plan first. Then you can do quick analysis on how deep the daylight can be brought to the building. If you think based on the measurement, you can get the credit, then you can continue to measure the daylight in the rest of the building. Approximately, the initial assessment is about 1 hour.

Additionally, I wouldn't worry so much about low angle sun except most of the rooms have windows on the south side only. If you can fulfill the requirement in the north part of your building, then you may need only 25% additional in the south part to get 75%. I concern more on the north part that only gets the daylight from the north sky which is less bright that the sky on the south. Moreover, you can adjust the time of the measurement if you get the problem with low angle direct sun.

Hope it helps..

Per the weather files, Boston-Logan will be about 1.5 times brighter at noon on March 15th than today. How low are your measurements? I believe you have the choice to apply the addenda that Todd mentions no matter when you registered the project. So you should just have to meet the minimum of 10 fc. Is the trouble meeting the minimum or the maximum?