3dsMax Design 2009 - Light Meters

[etboards17]

I have been playing a lot with the new features offered in 3ds MAX Design. The only thing I am confused about is the differences in the light meters. The images below are showing you different window options for a gym. All three of these have south facing monitor skylights, therefore regardless if there are clerestories or not, there should always be direct sun patterns on the floor.

In the three options you see below, option 5 has clerestories on the east and west walls, option 6 has clerestories on all walls, while option 7 has one clerestory opening on the north wall. Being that the clerestories are the only opening being modified, why is that the direct sunlight patters are changing?

[Steve_Bennett]

Ideally each building should be in the same location. Either in the same file with saved scene states that turns one building on and the rest off or separate files with each building in the same location in each file.

[etboards17]

At one time I did think that the location of the lighting system mattered relative to the models position. However, trial and error has resulted in finding the problem. Because each light meter was placed by hand, they were not in the same position per test room, so the results displayed different information.

The light meters set up in this scene were on a 4 by 4 grid. When doing this, the intense direct light coming through the skylights was in fact missing the light meter intersections, thus giving the illusion of no direct light. When I increased the amount of sections in the light meter by twice and three times as much. Less area was left unmeasured giving a more accurate reading. Now the scene is registering direct and indirect illumination correctly.

Having a sparse layout of cross sections in the light meter caused an innacurate display of light in the space.

[Steve_Bennett]

At one time I did think that the location of the lighting system mattered relative to the models position. However, trial and error has resulted in finding the problem. Because each light meter was placed by hand, they were not in the same position per test room, so the results displayed different information.

The light meters set up in this scene were on a 4 by 4 grid. When doing this, the intense direct light coming through the skylights was in fact missing the light meter intersections, thus giving the illusion of no direct light. When I increased the amount of sections in the light meter by twice and three times as much. Less area was left unmeasured giving a more accurate reading. Now the scene is registering direct and indirect illumination correctly.

Having a sparse layout of cross sections in the light meter caused an innacurate display of light in the space.

hmmm... - interesting - thanks for sharing what you found to work!

[etboards17]

New Issues: Since my previous post I have been doing multiple schematic designs and light studies. Very fun. Anyways, I found a nice way to animate the sun paths per weather data and did batch renderings to see a progression of the interior lighting on an hourly basis. Also, after running the batch render, the light meters would remember each hourly calculation and display them simply by using the time slider. This also enabled me to export the day lighting numbers per hour.

This is all very useful for schematic design, but how valid are these numbers? In office we are using 4 methods of light simulations: MAX Design 2009, Max 9 Radiosity, Analog light labs, and AGI; all of which are coming out with relatively the same effects, but numerically way different. This concerns me. How accurate is this light modeler?

Another question that has risen is what are the light meters able to record? In the image below you will notice that between 2 and 4 pm the light drop off is dramatic. This is making me wonder if the light simulation is not able to measure diffused light from a cloudy sky. WSSP requires that all rooms be measured with a diffused sky and I do not think MAX Design 2009 is using a diffused sky. In the settings there are a few sky models, one of which is CIE Overcast Sky. You would think that this sky model would be diffused light, but seeing the renderings progress through the day.... I have to wonder. There should not be a drop off of light between 2 and 4 pm, which makes me question the modeler completely. Seeing this effect kind of makes sense being that mental ray uses light rays to calculate its renderings. If there is not direct light in the room, then there is no light bouncing, thus resulting in low light levels, which is not at all a lighting simulation.

Any thoughts!?

[Steve_Bennett]

... How accurate is this light modeler?

Good question - I don't have numbers, but have heard from Autodesk that it is accurate - just not how accurate.

Another question that has risen is what are the light meters able to record? In the image below you will notice that between 2 and 4 pm the light drop off is dramatic. This is making me wonder if the light simulation is not able to measure diffused light from a cloudy sky. WSSP requires that all rooms be measured with a diffused sky and I do not think MAX Design 2009 is using a diffused sky. In the settings there are a few sky models, one of which is CIE Overcast Sky. You would think that this sky model would be diffused light, but seeing the renderings progress through the day.... I have to wonder. There should not be a drop off of light between 2 and 4 pm, which makes me question the modeler completely. Seeing this effect kind of makes sense being that mental ray uses light rays to calculate its renderings. If there is not direct light in the room, then there is no light bouncing, thus resulting in low light levels, which is not at all a lighting simulation.

Any thoughts!?

Are you placing mr sky portals at all building openings? Placement of portals at openings can also affect their performance.
Are you running with the Perez All Weather model for the sky? That is the only one designed to work with the light meters from my understanding.

[stusic]

Are you placing mr sky portals at all building openings? Placement of portals at openings can also affect their performance.
Are you running with the Perez All Weather model for the sky? That is the only one designed to work with the light meters from my understanding.

Man, you're smart! In 4 sentences, you've answered 15 questions I've had rolling around in my head...

[Steve_Bennett]

Man, you're smart! In 4 sentences, you've answered 15 questions I've had rolling around in my head...

Really? Cool!

[etboards17]

Are you placing mr sky portals at all building openings? Placement of portals at openings can also affect their performance.
Are you running with the Perez All Weather model for the sky? That is the only one designed to work with the light meters from my understanding.

I am using the Perez Sky model, but I have run extensive tests using the other sky models to compare to an onsite measurement. No portals

I uploaded a weather data file and the Perez Sky model updated itself displaying a certain diffused horizontal and direct normal luminance. I am guessing these numbers are specific to the location and date recorded. Now my question is, if it was a cloudy day when the lux numbers were recorded, would it be safe to say that I am using a cloudy day set of data? If so, then is the modeler simulating a cloudy day which has a substantial amount of diffused light and almost no direct light? It does not seem so...

[ramyhanna]

3DS Max Design 2009 should be getting you accurate foot/candle results. This program is recognized by LEED® as a valid lighting analysis program for getting you LEED® credits on your building. To better understand lighting analysis, click here to check out my blog on this topic.