[Radiance-general] Calculating maximum illuminance levels from daylight

[Ben Masters]

Just a quick one guys....

We are doing some radiance analysis on a  new building design. The 
building is to be located in Auckland, New Zealand (Southern Hemisphere, 
full of orcs and hobbits and elves). The design is a museum building that 
specifies a maximum of 350lux on a boat that is on display. We have to 
ensure that daylight (sunlight + skylight) does not give levels greater 
than this. We have designed the building to completely shade the boat 
surface from direct sunlight throughout the year. 

So, I have set up a numerical grid for analysis and ran the model under an 
overcast sky and then used local meterological outside illuminance data. 
This data gives a maximum diffuse illuminance of 50,000lux. 

Using this overcast sky model the design works. However, would this be the 
'worst case scenario'? I understand that a clear sky gives a greater 
luminance distribution around the horizon that an overcast sky. 

Following a shading analysis we have found that the most exposure to the 
sky and direct sunlight will be at 12pm during the winter solstice (June 
21) to the north facade. At this point the sun will be at an altitude of 
30 degrees.

In order to calculate absolute illuminace levels on the boat can I just 
use the CIE Clear sky model set up for this time period using the default 
values for horizontal diffuse irradiance and horizontal direct irradiance? 
Or do I have to specify the maximum values?


Thanks for your help
Ben

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