# ies photometry+geometry

**URL:** <https://discourse.radiance-online.org/t/ies-photometry-geometry/3564>\
**Category:** radiance-general\
**Created:** [April 28, 2007, 10:39am UTC](https://discourse.radiance-online.org/t/ies-photometry-geometry/3564 "2007-04-28T10:39:43Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Thomas\_Bleicher1](https://discourse.radiance-online.org/letter_avatar_proxy/v4/letter/t/8491ac/32.png) [@Thomas\_Bleicher1](https://discourse.radiance-online.org/u/Thomas_Bleicher1)\
**Post date:** [April 28, 2007, 10:39am UTC](https://discourse.radiance-online.org/t/ies-photometry-geometry/3564/1 "2007-04-28T10:39:43Z")

</div>

Great post, Rob!

Just one small addition:

> steve michel wrote:
> 
> > A linear fixture is exactly what I had in mind. For a while I even searched for 'bare bulb' photometry files from big lamp manufacturers (GE or Philips) but none exist for fluor tubes (only par and mr16 spots). But is the illum distribution method another one or a subset of using flatcorr and lboxcorr techniques you describe??
> 
> No photometric files exist for bare fluorescent tubes probably because you can't really test that condition, nor would anyone want to spend the money to do so. A fluorescent tube will always be in a fixture, even if it's a simple striplight -- a simple ballast housing and two lampholders.

If all you need is a T5 tube without complex reflector geometry behind it  
you can create a cylinder with the right brightness to match the output  
lumens of your lamp. The 'lampcolor' script calculates the right RGB values  
for you. Here is a sample session for a T5 35W lamp:

ble@zwielicht:~ lampcolor Program to compute lamp radiance\. Enter &#39;?&#39; for help\. Enter lamp type \[WHITE\]: Enter length unit \[meter\]: Enter lamp geometry \[polygon\]: cylinder Cylinder length \[1\]: 1\.449 Cylinder radius \[0\.1\]: 0\.008 Enter total lamp lumens \[0\]: 3300 Lamp color \(RGB\) = 80\.569890 80\.569895 80\.569895 Enter lamp type \[WHITE\]: ble@zwielicht:\~

The RGB values of 80.57 now go in a definition for the light material  
which in turn is used by the cylinder definition:

## light material for 35W T5 lamp  
void light light\_35W\_T5  
0  
3 80.57 80.57 80.57

## light applied to cylinder centred at (0,0,0) and aligned with x-axis  
light\_35W\_T5 cylinder lamp\_T5  
0  
7 -0.7245 0 0 0.7245 0 0 0.008

These four lines will create a bare T5 lamp that can be used as light  
source in Radiance scenes. The output distribution of a real lamp might  
be a tiny bit different (at the end caps for example) but I'd say it's  
close enough for lighting calculations.

You should not stick this lamp in complex reflector geometry and let  
Radiance do the calculations of the resulting distribution for you.  
The algorithms in Radiance are not suited for this kind of calculation.

Regards,  
Thomas

> **···**
>
> On 27 Apr 2007, at 01:21, Rob Guglielmetti wrote:

---

<div class="post-metadata">

**Author:** ![steve\_michel](https://discourse.radiance-online.org/letter_avatar_proxy/v4/letter/s/f4b2a3/32.png) [@steve\_michel](https://discourse.radiance-online.org/u/steve_michel)\
**Post date:** [April 29, 2007, 10:03am UTC](https://discourse.radiance-online.org/t/ies-photometry-geometry/3564/2 "2007-04-29T10:03:03Z")

</div>

Thomas,

Thanks for the tip. Using bare lamp photometry can be useful in architectural lighting geometry (eg. cove lighing, cornices etc..) that don't require complex fixtures other than a lamp holder and wiring.

Steve

> **···**
>
> > From: Thomas Bleicher \<tbleicher@arcor.de\>  
> > Reply-To: Radiance general discussion \<radiance-general@radiance-online.org\>  
> > To: rpg@rumblestrip.org,Radiance general discussion \<radiance-general@radiance-online.org\>  
> > Subject: [Radiance-general] Re: ies photometry+geometry  
> > Date: Sat, 28 Apr 2007 11:39:43 +0100
> > 
> > Great post, Rob!
> > 
> > Just one small addition:
> > 
> > On 27 Apr 2007, at 01:21, Rob Guglielmetti wrote:
> > 
> > > steve michel wrote:
> > > 
> > > > A linear fixture is exactly what I had in mind. For a while I even searched for 'bare bulb' photometry files from big lamp manufacturers (GE or Philips) but none exist for fluor tubes (only par and mr16 spots). But is the illum distribution method another one or a subset of using flatcorr and lboxcorr techniques you describe??
> > > 
> > > No photometric files exist for bare fluorescent tubes probably because you can't really test that condition, nor would anyone want to spend the money to do so. A fluorescent tube will always be in a fixture, even if it's a simple striplight -- a simple ballast housing and two lampholders.
> > 
> > If all you need is a T5 tube without complex reflector geometry behind it  
> > you can create a cylinder with the right brightness to match the output  
> > lumens of your lamp. The 'lampcolor' script calculates the right RGB values  
> > for you. Here is a sample session for a T5 35W lamp:
> > 
> > ble@zwielicht:~ lampcolor Program to compute lamp radiance\. Enter &#39;?&#39; for help\. Enter lamp type \[WHITE\]: Enter length unit \[meter\]: Enter lamp geometry \[polygon\]: cylinder Cylinder length \[1\]: 1\.449 Cylinder radius \[0\.1\]: 0\.008 Enter total lamp lumens \[0\]: 3300 Lamp color \(RGB\) = 80\.569890 80\.569895 80\.569895 Enter lamp type \[WHITE\]: ble@zwielicht:\~
> > 
> > The RGB values of 80.57 now go in a definition for the light material  
> > which in turn is used by the cylinder definition:
> > 
> > ## light material for 35W T5 lamp  
> > void light light\_35W\_T5  
> > 0  
> > 3 80.57 80.57 80.57
> > 
> > ## light applied to cylinder centred at (0,0,0) and aligned with x-axis  
> > light\_35W\_T5 cylinder lamp\_T5  
> > 0  
> > 7 -0.7245 0 0 0.7245 0 0 0.008
> > 
> > These four lines will create a bare T5 lamp that can be used as light  
> > source in Radiance scenes. The output distribution of a real lamp might  
> > be a tiny bit different (at the end caps for example) but I'd say it's  
> > close enough for lighting calculations.
> > 
> > You should not stick this lamp in complex reflector geometry and let  
> > Radiance do the calculations of the resulting distribution for you.  
> > The algorithms in Radiance are not suited for this kind of calculation.
> > 
> > Regards,  
> > Thomas
> > 
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