I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The average annual illuminance results for the tightly-packed single window case are 17% higher (42 vs. 49 lux) than the single window case. Don't know why.tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (-ar)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?

Model particulars: 40'x40' room, 3' sill, 9' wall, south-facing, 5' cubicle walls, average annual illuminance was calculated using the OpenStudio Radiance measure's daylighting control sensor just inside west exterior wall behind first cubicle wall, all materials (windows, walls, etc.) are exact copies in both cases. The only difference is 3x4 windows (13, <1" apart) vs. a single 40x4' window. Not exactly the same WWR, but close.

Radiance parameters: -ab 10 -ad 65536 -as 512 -dj 1 -dp 1 -dt 0 -dc 1 -lw 1.52e0-05, not 3-phase, just glass (i.e. "uncontrolled" in OS Radiance-speak). The -ar is the default which is 256 I think.

Here's the link: The results are ready to examine in DView. For the ...30_34 space, for the individual window file (...74.osm), the average annual illuminance of the daylight sensor is around 49 lux, whereas it is 42 in the ribbon window file (...75.osm). I've run them a few times to check for "stochastic" variance but it always turns out this way.

I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The average annual illuminance results for the single window case are 17% higher (42 vs. 49 lux) than the tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (-ar)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?

Model particulars: 40'x40' room, 3' sill, 9' wall, south-facing, 5' cubicle walls, average annual illuminance was calculated using the OpenStudio Radiance measure's daylighting control sensor just inside west exterior wall behind first cubicle wall, all materials (windows, walls, etc.) are exact copies in both cases. The only difference is 3x4 2x3 windows (13, <1" (17, 4" apart) vs. a single 40x4' 40x3' window. Not exactly the same WWR, but close.

Radiance parameters: -ab 10 -ad 65536 -as 512 -dj 1 -dp 1 -dt 0 -dc 1 -lw 1.52e0-05, not 3-phase, just glass (i.e. "uncontrolled" in OS Radiance-speak). The -ar is the default which is 256 I think.

Here's the link: The results are ready to examine in DView. For the ...30_34 space, for the individual window file (...74.osm), the average annual illuminance of the daylight sensor is around 49 lux, whereas it is 42 in the ribbon window file (...75.osm). I've run them a few times to check for "stochastic" variance but it always turns out this way.

I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The average annual illuminance results for the single window case are 17% 50% higher (42 vs. 49 (20 vs. 30 lux) than the tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (-ar)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?

Model particulars: 40'x40' room, 3' sill, 9' wall, south-facing, 5' cubicle walls, average annual illuminance was calculated using the OpenStudio Radiance measure's daylighting control sensor just inside west exterior wall behind first cubicle wall, all materials (windows, walls, etc.) are exact copies in both cases. The only difference is 2x3 windows (17, 4" apart) vs. a single 40x3' window. Not exactly the same WWR, but close.

Radiance parameters: -ab 10 -ad 65536 -as 512 -dj 1 -dp 1 -dt 0 -dc 1 -lw 1.52e0-05, not 3-phase, just glass (i.e. "uncontrolled" in OS Radiance-speak). The -ar is the default which is 256 I think.

Here's the link: The results are ready to examine in DView. For the ...30_34 space, for the individual window file (...74.osm), the average annual illuminance of the daylight sensor is around 49 lux, whereas it is 42 in the ribbon window file (...75.osm). I've run them a few times to check for "stochastic" variance but it always turns out this way.I have a similar case with 3x4 windows vs a single 40x4 window (50 vs. 60 lux).

I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The average annual ribbon window illuminance results for the single window case are 50% higher (20 vs. 30 lux) than the tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (-ar)? (ar?)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?

Model particulars: 40'x40' room, 3' sill, 9' wall, 2x3 windows, ~20% WWR, south-facing, 5' cubicle walls, average annual illuminance was calculated using the OpenStudio Radiance measure's daylighting control sensor map point just inside west exterior wall behind first cubicle wall, all materials (windows, walls, etc.) are exact copies in both cases. The only difference is 2x3 windows (17, 4" apart) vs. a single 40x3' window. Not exactly the same WWR, but close.wall.

Radiance parameters: -ab 10 -ad 65536 -as 512 -dj 1 -dp 1 -dt 0 -dc 1 -lw 1.52e0-05, not 3-phase, just glass (i.e. "uncontrolled" in OS Radiance-speak). The -ar is the default which is 256 I think.

I have a similar case with 3x4 windows vs a single 40x4 window (50 vs. 60 lux).

I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The ribbon window illuminance results for the single window case are 50% higher than the tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (ar?)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?

Model particulars: 40'x40' room, 2x3 windows, ~20% WWR, south-facing, 5' cubicle walls, illuminance map point sensor just inside west exterior wall behind first cubicle wall.

Radiance parameters: -ab 10 -ad 65536 -as 512 -dj 1 -dp 1 -dt 0 -dc 1 -lw 1.52e0-05

I've modeled a ribbon window as both a single, long window across a facade and as fairly tightly-packed individual windows. The ribbon window illuminance results for the single window case are 50% higher than the tightly-packed case.

I imagine the issue is the number of apertures in the tightly-packed case are causing some additive errors but don't know. Ideally I'd rather use the tightly-packed case as I'm also looking at glare at a particular location in addition to illuminance.

Which case is closer to reality? Can I get similar results if I up some Radiance parameter (ar?)? Can I reduce the error by grouping (clumping) a few windows together (i.e. a compromise with a few wide windows instead of ribbon)?