[Radiance-general] Radiance/blender/livi

Fri Jan 4 12:10:02 PST 2013

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

radiance-general-request at radiance-online.org wrote:

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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" <grobe at gmx.net>
>To: Radiance general discussion <radiance-general at radiance-online.org>
>Subject: Re: [Radiance-general] Radiance/Blender/LiVi
>Message-ID: <50E70327.1030303 at gmx.net>
>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? <aksel at gobo.io>
>To: Radiance general discussion <radiance-general at radiance-online.org>
>Subject: Re: [Radiance-general] why "global horizontal illuminance" is
>	smaller than "global horizontal radiation" multiplied by 179	in epw
>	file?
>Message-ID: <70844B7E-5F4B-4101-A48B-11CA35880E76 at gobo.io>
>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 <amcneil at lbl.gov>:
>
>> 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 <hope.zh at gmail.com> 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
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>> 
>> 
>> _______________________________________________
>> Radiance-general mailing list
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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
>aksel at gobo.io
>
>http://gobo.io
>
>
>
>
>
>
>
>------------------------------
>
>Message: 3
>Date: Fri, 4 Jan 2013 10:47:34 -0800
>From: Andrew McNeil <amcneil at lbl.gov>
>To: Radiance general discussion <radiance-general at radiance-online.org>
>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 at 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? <aksel at gobo.io> 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 <amcneil at lbl.gov>:
>>
>> > 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 <hope.zh at gmail.com> 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
>> > Radiance-general at radiance-online.org
>> > http://www.radiance-online.org/mailman/listinfo/radiance-general
>> >
>> >
>> > _______________________________________________
>> > Radiance-general mailing list
>> > Radiance-general at radiance-online.org
>> > 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
>> aksel at gobo.io
>>
>> http://gobo.io
>>
>>
>>
>>
>>
>> _______________________________________________
>> Radiance-general mailing list
>> Radiance-general at radiance-online.org
>> http://www.radiance-online.org/mailman/listinfo/radiance-general
>>
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