Glare calculations

Hello!

I'm using Desktop Radiance 2.0 and I've been making parametric calculations comparing daylight systems -a room with high reflectances, and the same room but adding in one case a lightshelf and in another an anidolic reflector. The room faces south, and I am evaluating them through daylight glare index.

I generated pictures with winrview, both looking into the window and looking sideways, and then used the two main glare routines available (findglare and glarendx).

According to other studies (including those of people who have used Radiance) the lightshelf should have a lower glare index than the room without any addition, but to my surprise and in the two picture cases, it is the opposite! (absolute illuminance levels are OK, though)

In the beggining I thought that my ceiling was too specular (50%) but then I changed it to another with similar reflectance but no specularity... and the results are still the same!

What could be wrong?

Carlos

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Hello Carlos,

I think it`s difficult to tell what can be the problem without more details.
Maybe the high reflectance in the ceiling is producing glare from the light
bounced by the lightshelf, even without specularity, but this is just a wild
guess. What are the reflectances and specularities of the lightshelf, floor,
walls and ceiling? It will also depend on the geometry of the room. You can
try with more ambient bounces to make sure the walls are getting all the
light they`re supposed to get...

Also, have you tried looking at the images? You can try reading the
luminances in the image and checking the contrast in the two cases. You can
also check the output from findglare, where there are listed all the glare
sources, against the images.
I`m sorry if I cannot be of much help, I`ve used glarendx only a few times.
Hope to be of some help, though.
Good luck and regards,

Santiago.

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-----Original Message-----
  From: [email protected]
[mailto:[email protected]]On Behalf Of Carlos Ochoa
  Sent: Monday, November 03, 2003 6:00 PM
  To: [email protected]
  Subject: [Radiance-general] Glare calculations

  Hello!

  I'm using Desktop Radiance 2.0 and I've been making parametric
calculations comparing daylight systems -a room with high reflectances, and
the same room but adding in one case a lightshelf and in another an anidolic
reflector. The room faces south, and I am evaluating them through daylight
glare index.

  I generated pictures with winrview, both looking into the window and
looking sideways, and then used the two main glare routines available
(findglare and glarendx).

  According to other studies (including those of people who have used
Radiance) the lightshelf should have a lower glare index than the room
without any addition, but to my surprise and in the two picture cases, it is
the opposite! (absolute illuminance levels are OK, though)

  In the beggining I thought that my ceiling was too specular (50%) but then
I changed it to another with similar reflectance but no specularity... and
the results are still the same!

  What could be wrong?

  Carlos

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  Do You Yahoo!?
   Todo lo que quieres saber de Estados Unidos, Am�rica Latina y el resto
del Mundo.
  Vis�ta Yahoo! Noticias.

Hi Santiago,

Thanks for the reply. To give more details, the room
measures 8x12 meters, with a ceiling height of 2.70 meters.
The window is 8x1.70m (placed on the 8m side).

The materials: ceiling: brushed aluminium (r=80%), walls:
beige (r=65%) and floor: blue (r=20%). These reflectances
were taken from recommendations from literature.

The light shelf has a length of 1m and is also made from
brushed aluminium and is placed 2.1 meters from the floor.
(half is inside the room and half outside).

I have already tried to include more ambient bounces, but
to no avail. But I will also check the contrast of the
images and check the sources of glare.

I hope this information can be useful!

Carlos

···

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