"Candelas Lumens and Lux" introduction to lighting  terms and calculations
"Candelas Lumens and Lux" introduction to lighting  terms and calculations




How to edit photometric files (IESNA, LDT, LTL, CIE etc)

You can edit these sorts of file by hand, but that is error prone and you have to keep by your side the definiton of the IES or LDT format to make sure you put the right numbers in the right places. With Photoview though all you have to do is type in the numbers and texts in the appropriate boxes. Here for example is a screenshot of the intensities table from a IESNA photometric file:

View mode of a photometric file editor

Simply click on the "Edit Mode" radio button and you will be able to change individual intensity values just by typing them into the grid. But you'll also be able to rotate, scale, mirror, average etc:

Going into edit mode  with the photometric file viewer

Let's have a closer look at the photometric editing commands which become active when you select Edit Mode:

How to edit photometry files easily

Most of the commands are self evident, but a few need more explanation:

Copy To: creates a new photometry (leaving the old one intact). You'll be presented with a dialog which lets you turn C-Gamma photometries into V-H photometries and vice versa. You can also choose the Gamma (or V) delta, and the C (or H delta) . If you want you can simply make an exact copy of the original photometry, or make a fully expanded version so you can edit into assymetry:

making modifyable copies of phtometries

Symmetrize to: With this command you can change the symmetry of the photometry. A copy is made and the original remains untouched. This is the dialog for this command:

Symmetrized Copy Photometry

Normalise: This function is used to make sure that all the Gamma=0 values are the same. You can select C planes to use for the normalization, or, if no C-Planes are selected then the averege of all the Gamma=0 is used. If you select more than one C-Plane then the average of the selected Gamma=0 values will be used.

Then, the rest of the photometry is scaled according to how the old gamma values had been scaled.

If you need to automate the editing of thousands of files then you might be interested in this article on batch file conversion for photometries.

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Contact me if you have any questions about this page or PhotoView photometric viewer. PhotoView is part of a set of services and programs from OxyTech which can be bought with a 10% discount. Click here to find out more.