Photometrics: What's the point

[CharlesD]

As far as I understand, photometrics are handled terribly in VW for lights that zoom. Please tell me if I'm missing something here.

 

A light is able to have a beam angle and a field angle. (It can also have both in a perpendicular axis, i.e. for PARs)

 

There is nothing in a light that references zoom range, so what I'm seeing most people do is put the Narrow Zoom Beam Angle in for "Beam Angle" and the Wide Zoom Field Angle in for "Field Angle".

 

Is this the best approach? Or should it be Narrow Zoom Field Angle for "Beam Angle"?

 

How does Candela respond to zoom range? As I understand it candela is a unit correlated to beam angle of the output.

 

So what Candela value am I supposed to put into the symbol of a light that zooms? Let's say I put the narrow zoom candela value in... then if I go to do photometric layouts it is going to be all wonky.

 

It seems like the answer is LIR needs Beam1 / Beam 2 / Field 1 / Field 2 / Candela -- NARROW as well as Beam 1 / Beam 2 / Field 1 / Field 2 / Candela -- WIDE. Then it needs a zoom slider thingy that adjusts those values in a proportionate relationship. No?

 

 

[RickR]

Since nothing in VW lets you change the zoom setting during rendering or photometrics, I just pick the setting I'm most likely to use. I suppose one could have multiple fixtures on many classes and render/calculate them as needed. When I set the beam and field as you suggest it's just to see the range of coverage when showing the beam.

 

I'm not fluent with Vision but I presume it has zoom controls that replace the VW settings when the project is converted.

 

Note that there can't be a universal relationship between zoom and candela. Each fixture uses it's own optics and so they behave differently and have different efficiencies.

[CharlesD]

16 hours ago, RickR said:

Since nothing in VW lets you change the zoom setting during rendering or photometrics, I just pick the setting I'm most likely to use. I suppose one could have multiple fixtures on many classes and render/calculate them as needed. When I set the beam and field as you suggest it's just to see the range of coverage when showing the beam.

 

I'm not fluent with Vision but I presume it has zoom controls that replace the VW settings when the project is converted.

 

Note that there can't be a universal relationship between zoom and candela. Each fixture uses it's own optics and so they behave differently and have different efficiencies.

Hey Rick. Thanks for these notes.

 

I think that the zoom functionality is something that's missing, and important though.

 

And what I'm suggesting with Candela is basically you provide the candela at the narrowest field of view as well as the beam/field angle at narrow field of view and  the candela at the widest field of view as well as the beam/field angle. While it's not scientific, I think assuming a direct relationship between zoom range and candela min/max would at least get you within an order of magnitude for your candela value along the zoom range. See the image in my first post. Basically I would input the NFOV and WFOV values into a fixture. This could be very helpful for me.

 

A very common task for me is this:

I have a fixed lighting position, I need to decide the quantity of lights to array on that position and how to focus them to achieve an average light level of X.

 

Right now Vectorworks doesn't allow me the tools to do that. As discussed, I can fake my zoom range using beam/field angles. But then I lose relationship to light output. It seems like zooming lights have been around for too long for VW to not have addressed this core functionality in the way it treats lights.

[CharlesD]

9 minutes ago, Rob Books said:

Because the lights in VW are static, for the most part, if you were trying to exactly match the zoom of a particular fixture you would need to go into it and adjust the beam and field angles on a per unit basis.  you can also adjust the candela at that point.  

a zoom is not an easy thing to do, as Rick said, it is not a linear grade, so to program how a zoom would work in the real world is not an easy task for a static rendering program like Vectorworks.  I think there are even problems with it in Vizualizers out there.  That being said, you can always put in a wish on the wish form and see if it takes off and gets traction.  

 

Best,

Rob.

Thanks Rob.

 

I don't totally understand what you are saying. What do you mean when you say lights are "static"?

[CharlesD]

31 minutes ago, Rob Books said:

in Vectorworks, you can only point them at one place at a time, whatever settings you give to them stick and without going in a readjusting them, there is no way to change things about the light.  the only thing you can relatively easily adjust is the intensity through the Visualizer slider.  Vectorworks is meant to give you a single moment in time for a look, and it can often take a lot of work to get it to look just right.

However, things like zoom, focus, color, etc. can be adjusted inside visualization software because it is connected to the Modes and all that they can control with either a real light board or a virtual one.  Visualizers are meant to allow you to see how a show would look from start to finish.  

What you are asking for here, the ability to Zoom a fixture, is more what software like Vision is for, not what Vectorworks is really for.

I hope that is a bit more clearly stated.  

 

Rob.

 

 

Thanks Rob. Now I see what you are saying. We are talking about two different things.

 

I do not want to make any changes over time, or in anyway previz. I am not asking for anything like what I would want out of Vision.

 

I'll post again when I can figure out a way to better phrase what I am trying to say.

[CharlesD]

Rob, let me try re-explaining this way:

 

Here is the VW built in VL-3500 Spot symbol. Note the following values:

 

Beam Angle - 10deg

Field Angle - 60deg

Candlepower - 1201000

 

This is not correct.

 

According to the manufacturer, this should be:

 

Beam Angle - 9deg

Field Angle - 10deg

Candlepower - 120100

 

What that means for me. Currently it is impossible in Vectorworks for me to layout lights and see both their coverage, and the amount of light they create, in any reasonable fashion.

 

Because this is a zoomable fixture, that is to say the angle of the beam of light is variable, the beam angle would more accurately be described as "9deg to 46deg". Vectorworks has no provision to deal with variable zoom lights.

 

As a work around, for zoomable lights everyone puts the narrowest zoom as the beam angle, and the widest zoom as the field angle.  That is why the built in VL-3500 Spot symbol is made the way it is. This allows you at least see the range of coverage you can get out of your light. Take a look at the attached Screenshot 1.

 

While doing this work around solves one problem, it creates another. It obliterates the usefulness of VW's photometric tools. Specifically, "Photometer" and "Photometric Grid".

 

Take a look at the Screenshot 1 again. See that my Photometer is telling me I should be receiving 34 FC of illumination at that point.

 

(As an aside: Obviously the Photometer tools make a lot of assumptions: no color, no shutters, no gobos, etc. But at least it gets me in the ballpark.)

 

Because the fixture is using the candlepower value of the light at its narrowest zoom and applying that to the area of widest zoom, this screenshot shows data that is entirely wrong.

 

As far as I know, Candlepower value cannot be changed on a per fixture basis. That means anyone wanting to use Spotlight for estimating light levels for a zoomable fixture is totally up the creek.

 

Because the angle of light and its candlepower are correlated, and you cannot adjust the candlepower of a spotlight fixture, that means if I want to create photometric evaluations of zoomable fixtures then I would need to have a discrete VW symbol for every beam angle. My library would look like this:

 

VL 3500 Spot - 9deg

VL 3500 Spot - 10deg

VL 3500 Spot - 11deg

VL 3500 Spot - 12deg

VL 3500 Spot - 13deg

VL 3500 Spot - 14deg

...etc...

VL 3500 Spot - 46deg

 

 

Let me know if that phrasing makes more sense?

Edited November 29, 2016 by CharlesD
Forgot to attach screenshots.

[CharlesD]

Thanks Rob.

 

I think it needs to be more in depth than just a min / max toggle. If we could have a slider that could adjust between the min/max values that would be super ideal! That would really make this tool functional.

[RickR]

As photometric functions go, I find VW pretty limited. I've spent years doing advanced calcs with programs from older Radiance and Lightscape to the current Dialux and AGI32. They are far more accurate, but since architectural fixtures rarely have zoom functions they don't that either. To be honest I'm not sure how accurate any of the theatrical visualizers are in pure photometrics.

 

I suggest you take your fixture data (like the original image) and use the closest approach you can in each instance. The more data you can get on each fixture type you use the better your approximations will be. Also recognise that there are major factors that can drop fixture brightness, old lamps, dirty fixtures, etc. No need to chase precision without accuracy.

 

[CharlesD]

On 11/30/2016 at 9:42 AM, Rob Books said:

the problem with that is that the zoom is not necessarily a linear progression from min to max, so how do you programically do that?  not an easy thing to do.  look at a photometric chart for several different zoom fixtures and you will see different data along the zoom.  I would have to put in a lot of data for just those few fixtures, and that means I don't have time for new content.  Trade offs.

 

Rob.

 

Hey Rob-

 

I think there's to things at play here, and they relate to each other.

 

1- The modeling of zoom in VW. This is necessarily linear between the min and max, and I imagine pretty straight forward from a programming perspective?

 

2- After we get the zoom sorted in VW. We can improve the photometric functionality. Regarding how zoom relates to candela, this is understood:

 

We don't need more than two data points to get a useful approximation. Using min and max beam angle/candela values we can created a weighted average for any discrete beam angle in the range. With the generous support of a friend, here is a screenshot from an excel spreadsheet that is the exact formulas I'm asking VW to have. This spreadsheet takes the min/max data point, you enter a discrete angle along that range, and it creates a weighted average. If this could be fed into the Candlepower field in VW it would make this all work.

 

(This screenshot example is also for the VL-3500 spot.)

[CharlesD]

9 hours ago, RickR said:

As photometric functions go, I find VW pretty limited. I've spent years doing advanced calcs with programs from older Radiance and Lightscape to the current Dialux and AGI32. They are far more accurate, but since architectural fixtures rarely have zoom functions they don't that either. To be honest I'm not sure how accurate any of the theatrical visualizers are in pure photometrics.

 

I suggest you take your fixture data (like the original image) and use the closest approach you can in each instance. The more data you can get on each fixture type you use the better your approximations will be. Also recognise that there are major factors that can drop fixture brightness, old lamps, dirty fixtures, etc. No need to chase precision without accuracy.

 

 

I agree that the Architectural products are better for serious modeling. But I also agree that they are not really practical to the Entertainment workflow. On Entertainment projects I only dip into architectural modeling for a proof of concept.

 

I definitely recognize there's a lot of assumptions being made for the "perfect" calculation. Though in fairness those same assumptions happen in Architectural as well. But for my workflow and the projects I do, getting close is good enough. If I really needed precise calculations I'd be doing it in an architectural program.

 

I think the genius of this though is that VW could be the only program to handle zooming instruments in an intelligent way.

[CharlesD]

On 12/5/2016 at 7:40 AM, Rob Books said:

Put in An enhancement request for this, that is how things are changed.  Maybe @JimWcan move this thread over there, get your lighting design buddies to vote it up.

 

Rob.

 

Cool thanks!