Data

Preliminary lighting models

As you can see the preliminary model is fairly rough, and it took quite some time to refine it to reach the final version.
  Click on the image to enlarge.

Luminance measurements and reflectance calculations

Reflective surfaces

Surface	Material exposure reading	Grey card exposure reading	Percentage reflectivity
Bookcases
	5.63	5.62	19.3%
Books
Dark	2.85	5.61	5.9%
Med	5.69	4.09	36.0%
Light	8.06	4.06	72.0%
Carpet*
Mixed green	2.09	4.01	7.8%
Pink	2.81	4.01	9.0%
Green border	2.04	4.00	5.9%
Carved wooden panel
	2.87	4.02	12.7%
Mullions
	2.00	2.09	9.6%
Painted walls
	8.05	4.09	54.6%
Tabletops
	8.00	5.60	36.0%
White plaster ceiling (estimated**)
	-	-	62.7%
Wood-fiber ceiling tiles (estimated**)
	-	-	23.8%

Exposure readings are in f-stops with the meter set for ISO 100 film and 1/8 of a second exposure.

* Measurements of the reflectivity of the carpet are almost certainly incorrect, since they would make it nearly black. We think it likely we stood in the light or something equally silly while taking them.

** These reflectivities were estimated by reference to adjacent materials; in the case of the white ceiling, the wall, and in the case in the case of the brown fiber ceiling tiles the adjacent white ceiling. This approach accumulates errors, but, lacking a ladder and the permission to use it, is probably the best we can do.

Emissive surfaces

We also took luminance measurements for two computer terminals sited in the reading room, more out of curiousity than anything else. We computed a relative luminance number for light and dark areas on the screen of an old green-screen Wyse terminal and a newer PC monitor. The Wyse terminal, which had heavy veiling reflections, was quite low contrast.

Surface	Material exposure reading	Grey card exposure reading	Percentage relative luminance
Green monitor
Background	4.00	5.67	5.5%
Foreground	5.64	5.67	14.6%
PC monitor
Background	2.00	4.00	4.5%
Foreground	5.62	4.00	41.4%

Color measurements

Materials

RGB values are given on a 0-255 scale. If your system's monitor is calibrated and your browser honors ICC color profiles, you should be seeing what we saw when we matched the color swatches with our computer's monitor. If you want to be sure, download the images and use Photoshop to view them.

** No values for the carpet because we do not have accurate reflectances values for it.

Luminaire measurements

These have turned out to be the hardest measurements. The original specification called out a 400W 3700º K, 65 CRI metal halilde lamp, and specified that the fixture would direct most of the light at 110-130º above the ground. Unfortunately, exact photometric data was unavailable, so we ended up estimating it.