Approximating the gross daylight flux through venetian blinds

John -


N.S. Campbell and J.K. Whittle

Thanks for that.

Interestingly the v. helpful C & W paper, although

expressing sentiments that are bang on target,

seems to compare one simulation with another,

but not with real-world empirical data, unless I�m

missing something.

Maybe up to some point, comparisons of their

Monte Carlo results with some similar simulation

in Radiance could be interesting/useful, but surely

not as useful as comparison with some real-world

empirical data.

Desperate for any kind of confirmation, my very

rough lux-meter measurements of office blind

overall transmission on an overcast London

day compared tolerably with their simulations.

I�m hoping some better real-world data will

come to light eventually.

.... just how useful is a daylight factor

evaluation for the scenario you describe.

Surely, the blinds are there also to control

direct sunlight? Perhaps even it is their

main purpose.

On the subject of control of direct sunlight by

blinds; despite having more than a suspicion

that you know more about daylighting than

I do, here goes:

The reason I said I was �not interested� in

direct sunlight in those studies was that for me

at least, in the UK, the �overcast sky� is the most

useful environment to apply in daylight studies

at the early stages of building design development.

It allows alternative architectural designs to be

compared for degrees of compliance with

particular published UK CIBSE and BCO

criteria so as to merit the alternatives'


I find that the usual objective for these sorts of

study is to find the daylight factor with �venetian

blinds down, slats horizontal, overcast sky�.

The control of direct sunlight by the venetian

blinds need not figure in these early simulations,

despite that being their major function.

Any fixed solar shading does of course have

to be modelled reasonably well, as do the

relevant parameters for the solar transmission

of the fa�ade and glazings; the geometry and

reflectance of the building model and its context.

Agreed nevertheless that if one could develop

a function to simulate blinds, then not allowing

the direct factor to be simulated would be

somewhat perverse.

Regards, George Chadwick


ALL-NEW Yahoo! Messenger - all new features - even more fun!