Design Information

Photometric Files

BSDF Files

The photometry of optical daylighting systems is best described with Bi-directional Scatter Distribution Function (BSDF) files that describe in simple terms the distribution of outgoing light relative to the direction of incoming light.  This BSDF file is in the standard XML file format that is used by the Lawrence Berkeley National Laboratories (LBNL) Window 7.X software that utilizes the growing Complex Glazing Data Base (CGBD) as well as the standard format used in the Radiance software.  Two files are provided, one at a lower standard Klems (145 patch) resolution and one with a 4x higher density variable resolution.  The standard Klems file is adequate for analyzing the workplane performance of a LightLouver installation or the general light in the space.  However, if glare or detailed rendering and luminance based analysis is performed, the higher density variable resolution file must be used as it better describes LightLouvers unique and impressive ability to direct the outgoing light precisely above the horizontal direction.  When using either file in the Radiance software, care must be taken to use appropriate Radiance parameters to properly sample the large amount of light coming from the LightLouver units.  In particular care must be taken in setting the ambient settings, at a minimum use: -ad of 4096 or higher, -ar  of 60 (and adequate for detail in scene), -ab 3 or higher.

LightLouver Standard Klems BSDF (general illuminance analysis)

LightLouver Variable Resolution BSDF (glare analysis)

Right click and select "save link-as" to download file to your computer.  The Klems file is already built-in and provided with the SPOT Pro software which makes daylighting analysis a breeze.

IES Photometric Files

Photometric files for the LightLouver Daylighting System in the Illumination Engineering Society of North America (IESNA) standard (*.ies) format have been created for many project locations.   These IES photometric files can be used in static lighting simulation tools to model the daylighting performance of the LightLouver Daylighting System.

 IES files are available in 5o increments up to 60o latitude.  The following table provides links to download the IES photometric files for the corresponding latitude:

5deg 25deg 45deg
10deg 30deg 50deg
15deg 35deg 55deg
20deg 40deg 60deg

Instructions for using the LightLouver IES photometric files are presented below.  These instructions are also downloadable here.


The photometric files (IES files) for the LightLouver Daylighting System describe the amount and distribution of daylight they provide under various orientations, glazing and sky conditions.  These IES files are valid for latitudes +/- 2.5o of the stated latitude and are provided for due east, south and west facade orientations.  They are all created for a longitude aligned with a prime meridian (0, 15, 30, 45...) such that noon sees the solar disc with an azimuth angle close to 0deg from south.  Other locations with longitudes further from a prime meridian will see the same amount of light and same solar paths but the exact azimuth angles of the sun at specific hours will vary to the right or left.

The IES file distribution is independent of the size of the window and can be adjusted to match the size of window being simulated,   You will need to enter the size of the window into the IES file before applying to a lighting model.  To do this open the file for the day being simulated, the files follow this naming convention:

"5x2_40.0_0.0_3_22_11.00_1.ies" = basewindowsize_latitude_orientation_month_day_time_skycondition.ies

There are IES file sets for every 5deg latitude band from 5o to 60o.  The orientation will be a number between -180 and 180 and describes to the orientation of the LightLouver window relative to due south.  South equals zero with negative angles going to the east and positive angles going to the west.  The time is solar time in military decimal form so 15.00 would equal 3:00PM during the winter, or 4:00PM during daylight savings.  The orientation listed is fairly valid for facades that are within +/- 7o.  The sky condition indicates the CIE type where 1 is a clear sunny sky and 3 is a overcast sky.

Open the file of interest in any text editor and you will have to edit the line after "TILT=" .  The header should look something like this when first opened:

[TEST]Generated by TracePro Release: 7 0 2 
1 67640.983322 1.000000 37 73 1 1 1.000000 0.000000 0.000000
1 1  1
  • You replace the 3rd number (1.000000 in the example abover) with the result of (area/10) * (Tvis/.76).  Area is in square feet, Tvis is the visible transmittance of the glass in decimal form.

  • You replace the 8th number with width of the window in feet.

  • You replace the 9th number with the height of the window in feet.

So, for example, the resulting header for a 2'3" high x 6'6" wide window with 70% glass transmittance should look like:

[TEST]Generated by TracePro Release: 7 0 2 
1 67640.983322 1.347 37 73 1 1 6.5 2.25 0.000000
1 1  1
  • Note the 3rd number = ((2.25*6.5)/10) * (70/76) = 1.347

The LightLouver IES files define the 0o vertical angle as perpendicular to the window, pointing into the room (IES files for electric lighting typically define this as down or nadir) and the 0o horizontal angle as up or zenith (this is typically the long axis).

There are 36 files for each orientation.  35 files that represent every daylit hour on the winter solstice, equinox, and summer solstice.  The last file represents an IES cloudy sky condition for an equinox sky at noon with a global illuminance of about 1300fc.  This file can be used to represent all cloudy conditions, the results should just be scaled appropriately with this multiplier: global illuminance / 1300.

Please let us know if you have any questions or problems using these files for simulation.  An automated website tool is in the works, so please be patient and stay tuned.