I am a new Radiance user/developer, and I am working on the calculation of
Solar Heat Gain through complex fenestration systems. I started learning
Radiance some time ago, and just an hour ago, a pretty obvious doubt came
to my mind:

If RADIANCE uses the RGB optical properties (that is, visible spectrum, I
If the materials change the spectrum of the radiation in every bounce, how
is it possible to just use the classic "179*(0,265*R+0,67*G+0,065*B)" to
compute the illuminance?

THANKS VERY MUCH

Germán Molina

PS: Sorry to bother with rookie questions, but I am the only person in my

Hi Germán,

Radiance (the software) does indeed work in radiometric values at its core, and the 179*(blah blah blah) is a valid conversion to illuminance. If you have very saturated colors in your model, I suppose they could throw off the calculation, but I think it'd take a lot to affect the accuracy. That said, this is why I do all of my modeling in greyscale, and use the "white" light source color for all electric lights.

There are a bunch of posts in the archives about this topic, and doing a higher resolution spectral rendering, and the validity of the 179 multiplier (which is somewhat arbitrary, but as long as you use that same multiplier going in each direction, you should be good to go.

Rob Guglielmetti
National Renewable Energy Laboratory (NREL)
Commercial Buildings Research Group
15013 Denver West Parkway MS:RSF202
Golden, CO 80401
303.275.4319
[email protected]

···

On 11/28/12 12:26 PM, "Germán Molina Larrain" <[email protected]<mailto:[email protected]>> wrote:

I am a new Radiance user/developer, and I am working on the calculation of Solar Heat Gain through complex fenestration systems. I started learning Radiance some time ago, and just an hour ago, a pretty obvious doubt came to my mind:

If RADIANCE uses the RGB optical properties (that is, visible spectrum, I suppose); how comes that it calculates the Radiance instead of Illuminance? If the materials change the spectrum of the radiation in every bounce, how is it possible to just use the classic "179*(0,265*R+0,67*G+0,065*B)" to compute the illuminance?

THANKS VERY MUCH

Germán Molina

PS: Sorry to bother with rookie questions, but I am the only person in my University using RADIANCE.

Thanks for the quick response Bob!

It is a little bit clearer now, But. the radiance considered by the
software is, then, only the visible part of the sun's radiance? If I
wanted to compute the total solar radiation (including IR and UV). Should I
compute (,265*R+.67*...)/vf ; where "vf" is the visible fraction of the
solar spectrum?

Thanks Very much!

···

2012/11/28 Guglielmetti, Robert <[email protected]>

Hi Germán,

core, and the 179*(blah blah blah) is a valid conversion to illuminance. If
you have very saturated colors in your model, I suppose they could throw
off the calculation, but I think it'd take a lot to affect the accuracy.
That said, this is why I do all of my modeling in greyscale, and use the
"white" light source color for all electric lights.

higher resolution spectral rendering, and the validity of the 179
multiplier (which is somewhat arbitrary, but as long as you use that same
multiplier going in each direction, you should be good to go.

Rob Guglielmetti
National Renewable Energy Laboratory (NREL)
Commercial Buildings Research Group
15013 Denver West Parkway MS:RSF202
Golden, CO 80401
303.275.4319
[email protected]

On 11/28/12 12:26 PM, "Germán Molina Larrain" <[email protected]<mailto: > [email protected]>> wrote:

I am a new Radiance user/developer, and I am working on the calculation of
Solar Heat Gain through complex fenestration systems. I started learning
Radiance some time ago, and just an hour ago, a pretty obvious doubt came
to my mind:

If RADIANCE uses the RGB optical properties (that is, visible spectrum, I
If the materials change the spectrum of the radiation in every bounce, how
is it possible to just use the classic "179*(0,265*R+0,67*G+0,065*B)" to
compute the illuminance?

THANKS VERY MUCH

Germán Molina

PS: Sorry to bother with rookie questions, but I am the only person in my

_______________________________________________
[email protected]

Hi Germán,

When the software is left to its own devices, it is considering beyond the visible range. You can get radiance and irradiance, and this is the default output. Radiance (the software) is often used for estimating solar resource for PV; applying V-lambda is always a second step that is available, in order to weight the radiometric values to photometric values (luminance or illuminance). I don't do much with radiometric values, but we would like to do more of that in OpenStudio.

Perhaps some others can weigh on with their experience looking beyond visual range.

- Rob

···

________________________________________
From: Germán Molina Larrain [[email protected]]
Sent: Wednesday, November 28, 2012 1:26 PM

Thanks for the quick response Bob!

It is a little bit clearer now, But. the radiance considered by the software is, then, only the visible part of the sun's radiance? If I wanted to compute the total solar radiation (including IR and UV). Should I compute (,265*R+.67*...)/vf ; where "vf" is the visible fraction of the solar spectrum?

Thanks Very much!

2012/11/28 Guglielmetti, Robert <[email protected]<mailto:[email protected]>>
Hi Germán,

Radiance (the software) does indeed work in radiometric values at its core, and the 179*(blah blah blah) is a valid conversion to illuminance. If you have very saturated colors in your model, I suppose they could throw off the calculation, but I think it'd take a lot to affect the accuracy. That said, this is why I do all of my modeling in greyscale, and use the "white" light source color for all electric lights.

There are a bunch of posts in the archives about this topic, and doing a higher resolution spectral rendering, and the validity of the 179 multiplier (which is somewhat arbitrary, but as long as you use that same multiplier going in each direction, you should be good to go.

Rob Guglielmetti
National Renewable Energy Laboratory (NREL)
Commercial Buildings Research Group
15013 Denver West Parkway MS:RSF202
Golden, CO 80401
303.275.4319<tel:303.275.4319>
[email protected]<mailto:[email protected]>

On 11/28/12 12:26 PM, "Germán Molina Larrain" <[email protected]<mailto:[email protected]><mailto:[email protected]<mailto:[email protected]>>> wrote:

I am a new Radiance user/developer, and I am working on the calculation of Solar Heat Gain through complex fenestration systems. I started learning Radiance some time ago, and just an hour ago, a pretty obvious doubt came to my mind:

If RADIANCE uses the RGB optical properties (that is, visible spectrum, I suppose); how comes that it calculates the Radiance instead of Illuminance? If the materials change the spectrum of the radiation in every bounce, how is it possible to just use the classic "179*(0,265*R+0,67*G+0,065*B)" to compute the illuminance?

THANKS VERY MUCH

Germán Molina

PS: Sorry to bother with rookie questions, but I am the only person in my University using RADIANCE.

_______________________________________________
[email protected]<mailto:[email protected]>

The RGB channels in Radiance can be interpreted however you like. By default, they are interpreted as visible components, but if you change the emissions, reflectances, etc. to stand for different channels, that's what you'll get. Math is math.

-Greg

···

From: "Guglielmetti, Robert" <[email protected]>
Date: November 28, 2012 6:54:52 PM HST

Hi Germán,

When the software is left to its own devices, it is considering beyond the visible range. You can get radiance and irradiance, and this is the default output. Radiance (the software) is often used for estimating solar resource for PV; applying V-lambda is always a second step that is available, in order to weight the radiometric values to photometric values (luminance or illuminance). I don't do much with radiometric values, but we would like to do more of that in OpenStudio.

Perhaps some others can weigh on with their experience looking beyond visual range.

- Rob

________________________________________
From: Germán Molina Larrain [[email protected]]
Sent: Wednesday, November 28, 2012 1:26 PM

Thanks for the quick response Bob!

It is a little bit clearer now, But. the radiance considered by the software is, then, only the visible part of the sun's radiance? If I wanted to compute the total solar radiation (including IR and UV). Should I compute (,265*R+.67*...)/vf ; where "vf" is the visible fraction of the solar spectrum?

Thanks Very much!