Diffuse illuminance

Dear all,

If I want to calculate the diffuse illuminance resulted in at a point inside a room, do I just need to remove the "void light solar" and "solar source sun" from the sky.rad and run the simulation?

Best regards,
Dennis

Actually, you need the sun to produce the initial light, to be bounced around for the diffuse. So the basic idea is (props to Andy McNeill) you do a "normal" simulation with a full sun and sky, and then a second one with JUST the sun, and then subtract the latter from the former, to get the diffuse-only. The details are in Sarith's turotial, here: https://www.radiance-online.org/learning/tutorials/matrix-based-methods

- Rob

···

On 1/26/18, 10:32 AM, "TSANG Kai Kwong" <[email protected]> wrote:

    Dear all,
    
    If I want to calculate the diffuse illuminance resulted in at a point inside a room, do I just need to remove the "void light solar" and "solar source sun" from the sky.rad and run the simulation?
    
    Best regards,
    Dennis

How did you generate your sky definition? If it's from gensky you could just generate it using the -c, -i, -s, or -u options. The -c is the only one of these that is a representation of a somewhat realistic scene - completely overcast sky (inherently without direct sun). From the gensky manual page:

-s Sunny sky without sun. The sky distribution will correspond to a standard CIE clear day.
+s Sunny sky with sun. In addition to the sky distribution function, a source description of the sun is generated.
-c Cloudy sky. The sky distribution will correspond to a standard CIE overcast day.
-i Intermediate sky without sun. The sky will correspond to a standard CIE intermediate day.
+i Intermediate sky with sun. In addition to the sky distribution, a (somewhat subdued) sun is generated.
-u Uniform cloudy sky. The sky distribution will be completely uniform.

-Chris

···

From: TSANG Kai Kwong [mailto:[email protected]]
Sent: Friday, January 26, 2018 12:25 PM
To: [email protected]
Subject: [Radiance-general] Diffuse illuminance

Dear all,

If I want to calculate the diffuse illuminance resulted in at a point inside a room, do I just need to remove the "void light solar" and "solar source sun" from the sky.rad and run the simulation?

Best regards,
Dennis
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Hello Dennis,

If you want to calculate the "illuminance generated by the Skie's diffuse
illuminance", you can do what Christopher is suggesting. However, if you
want to also include the diffuse illuminance generated by, for example,
direct sun reflected on surface, the task is somehow harder.

In that case, I would calculate total illuminance (i.e. rtrace < points.pt

-I+ -ab 4 -ad 5000 ... octree.oct > total_illuminance.txt); and then

substract the direct one (rtrace < points.pt > I+ -*ab 0 octree.oct *>
direct_illuminance ) and then substract (diffuse = total_illumiannce-
direct_illuminance)

I hope that helps!

German

···

2018-01-26 14:50 GMT-03:00 Christopher Rush <[email protected]>:

How did you generate your sky definition? If it’s from gensky you could
just generate it using the -c, -i, -s, or -u options. The -c is the only
one of these that is a representation of a somewhat realistic scene –
completely overcast sky (inherently without direct sun). From the gensky
manual page:

-s Sunny sky without sun. The sky distribution will correspond to a
standard CIE clear day.

+s Sunny sky with sun. In addition to the sky distribution function, a
source description of the sun is generated.

-c Cloudy sky. The sky distribution will correspond to a standard CIE
overcast day.

-i Intermediate sky without sun. The sky will correspond to a standard CIE
intermediate day.

+i Intermediate sky with sun. In addition to the sky distribution, a
(somewhat subdued) sun is generated.

-u Uniform cloudy sky. The sky distribution will be completely uniform.

-Chris

*From:* TSANG Kai Kwong [mailto:[email protected]]
*Sent:* Friday, January 26, 2018 12:25 PM
*To:* [email protected]
*Subject:* [Radiance-general] Diffuse illuminance

Dear all,

If I want to calculate the diffuse illuminance resulted in at a point
inside a room, do I just need to remove the "void light solar" and "solar
source sun" from the sky.rad and run the simulation?

Best regards,
Dennis

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for viruses and acceptability of content

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