The Twilight Render Team shares tips, ideas, helpful hints, and more on using Twilight Render
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derei
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by derei » Wed Jan 29, 2014 8:45 pm
Because always I had hard times with understanding and using IES files, I decided it's time to put some light in it. And also, to share with you my findings.
Each field in the file must begin on a new line and must appear exactly in the following sequence:
- IESNA91
- [TEST] The test report number of your data
- [MANUFAC] The manufacturer of the luminaire
- TILT=NONE
- 1
- The initial rated lumens for the lamp used in the test or -1 if absolute photometry is used and the intensity values do not depend on different lamp ratings.
- A multiplying factor for all the candela values in the file. This makes it possible to easily scale all the candela values in the file when the measuring device operates in unusual units—for example, when you obtain the photometric values from a catalog using a ruler on a goniometric diagram.
Normally the multiplying factor is 1.
- The number of vertical angles in the photometric web.
- The number of horizontal angles in the photometric web.
- 1
- The type of unit used to measure the dimensions of the luminous opening. Use 1 for feet or 2 for meters.
- The width, length, and height of the luminous opening. It is normally given as 0 0 0.
- 1.0 1.0 0.0 (i have no idea what is this)
- The set of vertical angles, listed in increasing order. If the distribution lies completely in the bottom hemisphere, the first and last angles must be 0° and 90°, respectively. If the distribution lies completely in the top hemisphere, the first and last angles must be 90° and 180°, respectively. Otherwise, they must be 0° and 180°, respectively.
- The set of horizontal angles, listed in increasing order. The first angle must be 0°. The last angle determines the degree of lateral symmetry displayed by the intensity distribution. If it is 0°, the distribution is axially symmetric. If it is 90°, the distribution is symmetric in each quadrant. If it is 180°, the distribution is symmetric about a vertical plane. If it is greater than 180° and less than or equal to 360°, the distribution exhibits no lateral symmetries. All other values are invalid.
- The set of candela values. First, all the candela values corresponding to the first horizontal angle are listed, starting with the value corresponding to the smallest vertical angle and moving up the associated vertical plane. Then, the candela values corresponding to the vertical plane through the second horizontal angle are listed, and so on until the last horizontal angle. Each vertical slice of values must start on a new line. Long lines may be broken between values as needed by following the instructions given earlier.
Example of Photometric Data File
The following is an example of a photometric data file.
- image copied along with article text from Autodesk website
- GUID-4663133D-AC6A-4E3D-82E6-07814E5FD185-low.png (3.25 KiB) Viewed 19978 times
This article was copied from Autodesk website and it can be read completely at the following address: http://docs.autodesk.com/ACD/2013/ENU/i ... d30e153989
The sole purpose why I copied it instead of only placing a link is to ease the access to it for forum's readers. If by doing this I broke some copyright rules (despite the fact that I mentioned the source, I ask admins to remove the article and let only the link to it).
Last edited by
derei on Tue Jul 05, 2016 2:36 pm, edited 2 times in total.
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derei
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by derei » Thu Jan 30, 2014 8:51 am
but sometimes you need to tweak a file... and if you don't know how to do it, you are stuck.
I got a LED stripe IES file, but its power settings were for an entire stripe (5m)... imagine that light in a single spot. So, I had to change the values inside the file, to fit it for a single LED on the strip.
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Fletch
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by Fletch » Thu Jan 30, 2014 2:10 pm
yes, it's output will be for the whole light fixture. there is no IES file for a single "bulb"... but as you say, perhaps you can make one for a single LED. If so, I would put it into a spot light component, not on a light emitting suface, it will render looking great, and render faster than light emitter.
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derei
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by derei » Thu Jan 30, 2014 4:20 pm
Fletch wrote:yes, it's output will be for the whole light fixture. there is no IES file for a single "bulb"... but as you say, perhaps you can make one for a single LED. If so, I would put it into a spot light component, not on a light emitting suface, it will render looking great, and render faster than light emitter.
It was easy to change, I just lowered the power from 26W to 0.07W (approximate consumption for one LED), and the candela multiplier reduced accordingly.
You say that placing this IES in a Twilight Light will render much faster than using it in a LEM ?
I was planning to make a small triangle (because a square is actually 2 faces - triangles) and apply a material with IES on it. But if I understood correctly, it would render much faster as TL light element with IES ?
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Fletch
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by Fletch » Thu Jan 30, 2014 4:47 pm
yes, try loading it into a tiny spot light, make sure to make the radius of the light an accurate scale. (very tiny) and then load the ies file you created into the spot light.
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derei
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by derei » Thu Jan 30, 2014 5:00 pm
Fletch wrote:yes, try loading it into a tiny spot light, make sure to make the radius of the light an accurate scale. (very tiny) and then load the ies file you created into the spot light.
Can't do it "very accurate" because you limited the Spot Light RADIUS to 2.5mm (that's a 5mm diameter). Unless you can tell me how to tweak that, so I can reduce the size even more... no can do. It will allow me to input any value I wish, but it will not scale the component.
I don't know if scaling it in sketchup is the same thing.
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Fletch
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by Fletch » Thu Jan 30, 2014 8:13 pm
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