[Radiance-general] Evaluation

[Reinhart, Christoph]

Dear Alexa,

>>..., I was wondering how the architectual & lighting community (obviously
I'm not a member of it) uses RADIANCE.

Within the framewor of IEA Task 31, Daylighting Buildings in the 21st
century NRC carried out an online survey last year on "the current use of
daylight simulations during building design". You can download a copy of the
report from http://irc.nrc-cnrc.gc.ca/ie/light/survey. Key information from
the abstract are: 

"... Survey participants worked predominantly on offices and schools...
Tools' complexity and insufficient documentation were identified as
weaknesses of existing programs. Self-training was the most common training
method. Tool usage was significantly higher during design development than
during schematic design. Most survey participants used daylighting software
for parameter studies and presented the results to their clients as a basis
for design decisions. While daylight factor and interior illuminances were
the most common simulation outputs, shading type and control were the most
common design aspects influenced by daylighting analysis... While
participants used a total of 42 different daylight simulation programs, over
50% of program selections were for tools that use RADIANCE... " (In case you
need a more detailed version of the repor, let me know.)

>>Ian Ashdown says it better than I can, in his (excellent) "Thinking
Photometrically" coursenotes: "As for daylighting calculations, it is likely
that Jongewaard (1993) is correct - the results are only as accurate as the
accuracy of the input data. Done with care, it should be possible to obtain
±20 percent accuracy in the photometric predictions. However, this requires
detailed knowledge and accurate modeling of both the indoor and outdoor
environments. If this cannot be done, it may be advisable to walk softly and
carry a calibrated photometer."

I completely agree with this estimate. It reflects the results from John's
validation study on a façade with a clear glazing and our validation study
for a facade with venetian blinds. Finally, I am doing a validation study
right now for a translucent façade using "trans" and "transdata" (with a lot
of help from maitre Greg) and again I find comparable numbers. 

Christoph