[Radiance-general] Daylight factor

[Marija Velickovic]

Hi Victor,

For daylight factor calculation in Radiance you can use *dayfact* script
included in Radiance distribution.
It has interactive input ,so you can input all data you need, and it will
calculate Df and various related images.

If you want to calculate in only in few points, you can do it simple,
calculate illuminance in points inside the building for overcast sky (with
rtrace program), and just divide this values with overcast sky horizontal
illuminance value.
For example overcast sky for Paris for diffuse horizontal illuminance
10000lux
gensky 6 22 +11 -c -a 48.817 -o -2.483 -m -15 -B 55.866

-B is irradiance an is calculated as 10000/179=55.866

And rtrace command would be like:
rtrace -I+ -h- -oov -ab 5 -ad 1024 -as 256 -aa 0.15 -ar 1000 octree.oct|
rcalc -e '$1=$1; $2=$2; $3=$3;
$4=(0.265*$4+0.670*$5+0.065*$6)*179'<points.txt >output.txt


Note that you should put appropriate calculation parameters in rtrace to
have accurate results.
rcalc command above converts rtrace output from RGB to 1 illuminance value.

So when you got illuminances inside the building just divide them with
10000, to get DF values, or directly in rcalc divide with 10000 to get Df
values on output:
$4=(0.265*$4+0.670*$5+0.065*$6)*179/10000

Hope this helps,
Marija

On Thu, Dec 10, 2009 at 10:04 AM, Victor Li <victorpermanent at gmail.com>wrote:

> Dear:
>
> Daylight factors are expressed as the percentage of natural light falling
> on a work surface compared to that which would have fallen on a completely
> unobstructed horizontal surface under exactly the same sky conditions. Thus,
> a daylight factor of 5% on an internal surface means that it received only
> 1/20th of the maximum available natural light.
>
> so we can calculate daylight factor by RADIANCE with a overcast sky. Then i
> calculated the illuminance under overcast sky. I found the distribution of
> illuminance and skyfactor in the room is different. For example, in the room
> ratio of minimum to average of daylight and illuminance are quite different.
> Would you tell me the reason?
>
> Best Regards!
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://radiance-online.org/pipermail/radiance-general/attachments/20091210/f8492768/attachment.html