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




How to add (and subtract!) 2 photometric files together.

There are times when you want to add two different photometries together. This could because a single luminaire has been measured in two passes because it was mechanically impossible to do it all in one pass. Or maybe a single luminaire can be made up of two other luminaires joined together. Whatever the reason, you want to be able to add the two photometries together to form a single new photometry.

With PhotoView this is very easy, here is the dialog to do it:

Rotate and join photometries

In the above example we have rotated the first photometry 180 degrees because it is the part of the luminaire which lights with indirect lighting. The second photometry has not been rotated.

You can see the resultant photometry in the center of the dialog.

Here is another example, and in this case you can see that the photometry on the left has a higher flux than the one on the right. This causes the join (after rotation) to show the lower part of the new photometry to have more output than the upper part:

How to sum two photometries

The resulting photometric solid resulting from the sum of the two different ones is shown below:

Sum of two photometries

We have been using the "Candles Sum" so far, but another addition mode is the "Separated Measurements Sum" designed for when a single luminaire has been measured in two different instances, maybe because of mechanical reasons.

PhotoView can also be used to show the differences between photometries, instead:

Choose Absolute Difference in the photometry join dialog, click on Do Join and if you like what you see click on OK to create the new photometric file. The result of the example shown above is shown here as a polar diagram and photometric solid:

Photometric file subtraction and difference


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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.