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Had some questions on accurate Photometrics


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Hi there,

 

I am interested in using the Photometer and Photometric grid tools to predict staging light levels.

 

As I was playing around with the tools I was getting footcandle readings that seem to be much higher than listed on the manufacturer's report. For instance at a distance of say 16' when I would expect to get around 300 footcandles (based on the manufacturer's report) I am reading 450 foot candles in Vectorworks.

 

Are there any tips and tricks that I can use to get a more accurate prediction from Vectorworks? I tried playing around with where the photometer was placed (how centered on the beam it was, etc) but still no dice. 

 

I don't mind some variance, but it seems like Vectorworks is substantially higher in its predictions than what the manufacturer's report shows and if anything I'd rather have it the other way around.

 

Thank you!

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  • Vectorworks, Inc Employee

Make sure the data you are supplying the Vectorworks symbol is in candle power or peak candella, not Lux, Lumen or some other value. (It does NOT use the value from the VW light emitter.)

With that said Vectorworks uses a very simple cosine squared falloff calculation based on the distance from the source.

It does not take into account dimmer value, color, shadows, reflections or any other objects in the drawing.

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2 minutes ago, klinzey said:

Make sure the data you are supplying the Vectorworks symbol is in candle power or peak candella, not Lux, Lumen or some other value. (It does NOT use the value from the VW light emitter.)

With that said Vectorworks uses a very simple cosine squared falloff calculation based on the distance from the source.

It does not take into account dimmer value, color, shadows, reflections or any other objects in the drawing.

 

Hi there,

 

I am using a stock Vectorworks library symbol and have confirmed that it is using candellas.

 

Honestly not looking for Vectorworks to calculate things like color, dimmer value, etc. Just want it to get within spitting range of the manufacturer reports otherwise there's no point in using this functionality. I figure there may be something I am missing in how I have things laid out in Vectorworks?

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  • Vectorworks, Inc Employee

Check the values we have in our symbols. We assume a certain lamp type when we create the symbol and use the data that is available when we created the fixture. I know that some specifications have changed over the years and manufacturers have correct/updated their specification.

We have verified that that calculations we report are correct based on the methods in  Robert C. Mumm's Photometrics Handbook 2nd Edition.

The manufacturer's report probably uses actually measurements so they will always be more accurate.

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