Agi32 Forum

[Arnaude Kubiak]

Hi! I was wondering why does LEED require to run a simulation on the 21st of september?
It also requires to perform the simulation during a clear sky condition. However, with the software I used (AGI32) I can't calculate the daylight factor under a clear sky condition. Could someone give me some explanations?
Regarding the overcast sky, I would like to know which is the typical value used? I searched on Google but I got different answers...
Thanking you in advance

Xavier,
The reason simulations are typically run on the equinox is because the sun is at the equator, its neither at its highest or lowest altitude in the sky. You can run on March 21st or September 21st.

Daylight Factor calculation is different type of calculation than illuminance calculation. DF is calculation uses the CIE overcast sky value. DF is the percentage of the exterior horizontal illuminance value that reaches a point inside a space. Having a DF of 2% is good. Illuminance calculations is the value, either in lux or footcandles, on a point in building under all type of sky conditions.

There are alot of good books on daylighting, "Daylighting in Sustainable Building, Daylight in Buildings, "Sun, Wind, and Light". There are also a lot of good sources on the web that talk about daylighting strategies, the different types of metrics, calculations, etc. The Daylighting Collaborative, and the Whole Building Design Guide, are just few of the many sources that i suggest you may want to read to get a better understanding of daylight and daylight simulations.

Thank you so much, I don't have much experience in daylighting... May I ask you another question? What is the typical outdoor illuminance value used by the software for the overcast sky? I searched on Google but I got different answer... If you can help me with this, I'd really appreciate.
Thanks!

Are you asking what the typical illuminance is for a CIE overcast sky or just an overcast sky condition in general?
Off the top of my head i believe CIE overcast is 1000 lux. In the program, put a ground plane in, place a sensor at 30" facing up, run the simulation under the specific sky condition at noon, this will tell you what the computer program is using.

First off, this is a v3 forum, so calculating the daylight factor is not an option for v3 projects. If yo have a v2.2 or even a schools 2007 project, then you have the option to use the glazing factor calculation method. If you are going to be using the simulation method in v3, then you should be focusing on illumance calculation in AGI-32.

Ok, so you ran a sim with 333 fc, which to me is pretty low, for a CIE overcast sky. Not sure of of all your inputs etc, but that is low. 2% of 333 is rounded up to 7 fc which is well below any level for a regularly occupied space. Is the sensor facing up?

I would suggest that you look into AGI-32's help forum. I believe they have some video tutorials that can help you set your model for simulations. Make sure you have the task of setting up your model and getting all your input parameters correct. The biggest problem with simulations is incorrect input. This will always give you false reads. If you follow the false reads, you will actually make the incorrect design decisions. Part of knowing simulation is knowing when the outputs are false.

I am primarily a lighting designer using AGi32. When reading AGi32 forums it has been suggested that sketchUp was a way to pump up the model. That being said I would like to import a 3D map of a College Campus that is on hilly terrain to be able to light the walks, parking lots and streets and if possible show shadows.

As in the real world, if the sun is shining it's usually difficult to see interior lighting (dpending, of course, on sun angle, time of day, etc.). A 60 W lamp is no match for the lumen power of the sun. Try changing your sun/time of day settings and also try increasing the lumen output of your lamp. Maybe that will help.

I have found that I have to increase a 60w light up to 1000w or more to get the interior lighting to appear. Also, I have to set the time of day to dawn or dusk, so there is some exterior daylight but not enough to drown out the interior lights. I'm looking at the interior lighitng topics in the forum because I am curious why do I have to increase the interior lighting to 1000w / more in order to the correct look. Does this tell me that I don't have enough lights in the design and when the project is built I will have issue of not enough lights?????

A rendering is not a lighting calculation. It's a pretty picture. If you want to know whether you have sufficient light levels in your project, you need to do a lighting calculation with software like AGI32. A rendering is about the look and feel and composition of the design (i.e., the *quality* of the light). A lighting calculation is about the *quantity* light you are putting on work surfaces, in passageways, on the walls, etc. These are two very different things, so be sure you are using the right tool for the right purpose.

If you're lighting your interior with a table lamp and doing an exterior rendering, think about what the light is hitting- mainly the table it sits on, which may not even be visible from the outside. In your rendering, if you're looking through windows at the room's walls and wondering why they look so dim, it's because relatively little light is hitting them from that table lamp. Also, contrast is extremely important. The brighter your exterior, the harder it will be to see artificial lights inside.

Thanks Jlights. It was my assumption that with Revit, the idea was to have everything as real as possible including the rendering (which includes how the lights render). But you are correct, I will have to use a different tool to understand the light levels in the space. I am far from a lighting designer or consultant, so I probably couldn't begin to understand the complex lighting tools available.

You can see in the rendering I've produced using Revit. The daylight is set a dawn to reduce the amount of sunlight coming through the windows. I've increased the wattage on the lights to such a high level (1000 -1500w) to get the interior space to be lit.

Nice. I'm actually a lighting designer myself- if you don't mind a suggestion, I'd move those downlights on the right a bit farther away from the windows so you don't get that light scallop on the wood beam, which distracts from the attractive design of the space.

I'm guessing you did this rendering at Medium (though I could be wrong); if you do it at High or Best the edges of the light beams should soften and you won't have such hard edges on your beams of light. These also create a distracting pattern in the rendering. If you can soften them, your eye will be drawn right to the end of the hall where the light is brightest and you'll have a terrific rendering.

I usually add a light group of studio lights emitted from a 8'x8' rectangle shape uniform. make the FC about 100,000 for exterior daylight. starting from 100,000 you can double or cut in half the fc until you get the light you want. setting the time for dusk or dawn usually looks pretty good. studio lights are great for creating soft light to enhance your scene

yeah i use that and adding an ambient occlussion layer and a glow adjustment layer in photoshop to bring a little more focus onto the interior lights becuase the soft lights aren't "physically correct". all tricks i learned for a photographer

Thanks jlights - those are great suggestions. I'll move the recessed away from the wood beam. I'll do another render at best to see if the light beams are softer. but yes, that will make the rendering look nicer.

@alabaster2512 - i like the idea of your tricks. how do you set the studio lights to 100,000 FC (footcandles?) and what do you mean by creating light group of studio lights emitted from a 8'x8' rectangle shape uniform. do you place the studio lights in a 8'x8' spacing within the interior space to get the interior to glow?

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