Radiance/blender/livi

That's right Lars, it uses blender geometry to specify a grid of points and rtrace to calculate the numbers. Numbers are then expressed back in blender as coloured geometry.
Ryan

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Today's Topics:

  1. Re: Radiance/Blender/LiVi (Lars O. Grobe)
  2. Re: why "global horizontal illuminance" is smaller than
     "global horizontal radiation" multiplied by 179 in epw file?
     (Aksel Gro?)
  3. Re: why "global horizontal illuminance" is smaller than
     "global horizontal radiation" multiplied by 179 in epw file?
     (Andrew McNeil)

----------------------------------------------------------------------

Message: 1
Date: Fri, 04 Jan 2013 17:28:23 +0100
From: "Lars O. Grobe" <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] Radiance/Blender/LiVi
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Hi Ryan,

looks great! I am excited to see a Blender-based Radiance framework
alive again!

I had a quick look into some of the demonastration videos. The pixel-ish
shapre of the shadows and the term "receiver surface" - am I correct
that you make use of a point grid for the calculations, not rpict & friends?

Cheers, Lars.

------------------------------

Message: 2
Date: Fri, 4 Jan 2013 19:34:07 +0100
From: Aksel Gro? <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] why "global horizontal illuminance" is
smaller than "global horizontal radiation" multiplied by 179 in epw
file?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=iso-8859-1

Hi Andy,

Interesting rule. Could you recommend further reading for my interest on how to get to the number 179? I would like to get a tiny grasp on the underlying principle to better understand.

Thanks a lot,
Aksel

Am 02.01.2013 um 20:23 schrieb Andrew McNeil <[email protected]>:

Hi Ji,

179 is the efficacy of white (equal energy) light over the visible spectrum.

Daylight is composed of a broader spectrum, so the efficacy (visible light per watt of energy) is lower. Usually around 90 for the sun and 110 for the sky, but changes based on various factors.

179 is used in Radiance as a convention since we are simulating visible light. So when you're defining you sky using gensky with weather data you need to either use the measured illuminance values and divide by 179 to get radiometric units for the visible spectrum, or use the measured radiance values (for solar spectrum), multiply by an approximate efficacy, then divide 179 to get radiometric units for the visible spectrum only.

If you use gendaylit all the conversions are done for you.

Best,
Andy

On Tue, Jan 1, 2013 at 8:36 AM, Ji Zhang <[email protected]> wrote:
Dear list, Happy New Year!

I have a simple question related to conversion from irradiance value to illuminance value, and pls correct me if I'm wrong:

Usually we can estimate the illuminance (lux) for a given point by multiplying the irradiance (w/m2) for the point as simulated via Radiacne by 179 (lm/w) which is the luminous efficacy used in Radiance, or more strictly (R*0.265+G*0.670+B*0.065)*179.

However, it seems that in a epw weather file the "global horizontal illuminance" value is not equal to but smaller than the "global horizontal radiation" value multiplied by 179.

May I ask:
1. why there's such a large discrapency?
2. Will this lead to over-estimation of illuminance when using cumulative sky derived from "global horizontal radiation" ?

Thanks in advance!

- Ji

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--

Aksel Gro?
Dipl.Ing.Arch., Dipl.Szeno.

Electric Gobo
Sch?nhauser Allee 182
10119 Berlin, Germany

T +49 30 559 531 75
M +49 179 394 30 92
[email protected]

http://gobo.io

------------------------------

Message: 3
Date: Fri, 4 Jan 2013 10:47:34 -0800
From: Andrew McNeil <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] why "global horizontal illuminance" is
smaller than "global horizontal radiation" multiplied by 179 in epw
file?
Message-ID:
<CAOG+Niy1VuNOa5GZG-tg77Tsp+iiVqijZLjKFf4pbA9q7+yV7w@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Hi Aksel,
Unfortunately I don't have sources for this other than Greg's emails in the
vintage radiance digests (1990's). Search these pages for "179", there are
several emails on this topic):
http://radsite.lbl.gov/radiance/digests_html/v2n5.1.html
http://radsite.lbl.gov/radiance/digests_html/v2n9.html
Best,
Andy

On Fri, Jan 4, 2013 at 10:34 AM, Aksel Gro? <[email protected]> wrote:

Hi Andy,

Interesting rule. Could you recommend further reading for my interest on
how to get to the number 179? I would like to get a tiny grasp on the
underlying principle to better understand.

Thanks a lot,
Aksel

Am 02.01.2013 um 20:23 schrieb Andrew McNeil <[email protected]>:

> Hi Ji,
>
> 179 is the efficacy of white (equal energy) light over the visible
spectrum.
>
> Daylight is composed of a broader spectrum, so the efficacy (visible
light per watt of energy) is lower. Usually around 90 for the sun and 110
for the sky, but changes based on various factors.
>
> 179 is used in Radiance as a convention since we are simulating visible
light. So when you're defining you sky using gensky with weather data you
need to either use the measured illuminance values and divide by 179 to get
radiometric units for the visible spectrum, or use the measured radiance
values (for solar spectrum), multiply by an approximate efficacy, then
divide 179 to get radiometric units for the visible spectrum only.
>
> If you use gendaylit all the conversions are done for you.
>
> Best,
> Andy
>
>
> On Tue, Jan 1, 2013 at 8:36 AM, Ji Zhang <[email protected]> wrote:
> Dear list, Happy New Year!
>
> I have a simple question related to conversion from irradiance value to
illuminance value, and pls correct me if I'm wrong:
>
> Usually we can estimate the illuminance (lux) for a given point by
multiplying the irradiance (w/m2) for the point as simulated via Radiacne
by 179 (lm/w) which is the luminous efficacy used in Radiance, or more
strictly (R*0.265+G*0.670+B*0.065)*179.
>
> However, it seems that in a epw weather file the "global horizontal
illuminance" value is not equal to but smaller than the "global horizontal
radiation" value multiplied by 179.
>
> May I ask:
> 1. why there's such a large discrapency?
> 2. Will this lead to over-estimation of illuminance when using
cumulative sky derived from "global horizontal radiation" ?
>
> Thanks in advance!
>
> - Ji
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
> _______________________________________________
> Radiance-general mailing list
> [email protected]
> http://www.radiance-online.org/mailman/listinfo/radiance-general

--

Aksel Gro?
Dipl.Ing.Arch., Dipl.Szeno.

Electric Gobo
Sch?nhauser Allee 182
10119 Berlin, Germany

T +49 30 559 531 75
M +49 179 394 30 92
[email protected]

http://gobo.io

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