How does one make physical correct movie set lighting?

[SaCCo]

Maybe I have mis understood something completely basic. but could someone please help me understand this?

When I do my animations, I try to keep everythng as physical correct as possible.

So when I do a scene, I always start with the default Vray Sunlight.
Next and as on a real movie set I need to soften up the light contrast on the subject of my movie.

To do this I make some spotlights using the Vray Sphere (IE. 25 cm in diameter), and some floodlights/softboxes (IE. 0.8x 1.6 m) using the Vray Light planes.

This is all fine and dandy, but my problem is how do I know what to set the multiplier on for the lights?

I can go onto IE. Arri's site and read about their lights, but the way they meassure their light specs doesn't seem directly compateble to the options Vray gives me.

Here is another good example of a site with movie lighting.
http://www.gearrental.com/pages/light.htm

How do I imitate a these lights as closely as possiple in vray.
I can find their size (on IE a kinoflo) and their watt?

It would be nice to have a library of real movie lights one can use at will.

Thanks

[SaCCo]

More specificly

If I have a 1200W spot light. which is IE. 25cm in diameter.

Then I make a Vray Sphere at 12,5 cm in radius.
But what should I set my multiplier at? and why?

[joconnell]

Try and get a lumen rating of the light rather than wattage - wattage is the amount of power that the light uses but due to inefficiency it won't turn all of that power into light - if you get a lumen value of the light, it's the actual amount of light that it gives out.

[dlparisi]

Forgive my ignorance, but I'm curious what is 'IE' referring to ? My first assupmtion was internet explorer but that doesn't make sense with where it's being used.

[SaCCo]

IE.

I was under the impression that IE. ment somthing like "as an example".
Or put in another way.

"I set my light at IE. 25"
is the same as
"I set my light at, for the sake of this example, 25"

Its mean that its a non specific number, just a ball park figure.

But maybe I got it wrong?

[SaCCo]

Luma rating.

Well, here is a chart provided by Arri, on one of thier spots.
http://www.arri.com/prod/lighting/06...wid=L1.79610.B

Lux is not one of the Vray light options, if I recall correct?
So what do I need to do in this case?

[dlparisi]

Ahhh ! Makes more sense now, I thought it might refer to some techincal stage lighting term. A few things would make it more clear though. First, it actually means something more along the lines of "that is" rather than "for example" (which is usually abbreviated "e.g.") which is what you're trying to get across. It should normally be lower case, have periods after each letter and normally has a comma before and after (just like in your ", for the sake of this example," quote above). It also usually follows another term you're describing and does not fully replace the "for example" in the body of a sentence. More like this... "I set my light at a standard value, e.g., 25." or even ",.i.e., 25". Sorry for the grammar lesson . This is an informal forum after all.

For the light question, as joconnell said, try to get the lumen output of the lights (although Idon't see this on ARRI's website). Either way I'm not sure how accurate it'll be without a IES file to control the distribution of the light out of the fixture (I don't believe there are IES files available either). So at that point it's probably best just start pumping up the regular lights until they look good and then developing a library based on what works for you.

[dlparisi]

Luma rating.

Well, here is a chart provided by Arri, on one of thier spots.
http://www.arri.com/prod/lighting/06...wid=L1.79610.B

Lux is not one of the Vray light options, if I recall correct?
So what do I need to do in this case?

Lux is a measure of how much light is hitting a surface not how much light is put out by a lamp or fixture so that's doesn't help. I don't know if there's a way to convert lux into lumens though.

[SaCCo]

,.i.e., 25". Sorry for the grammar lesson . This is an informal forum after all.

No worries mate. Its always nice to improve a little on my english skills.



Yea, I guess your right about the best way for now is to just crank the multiplier up until the image looks like i want it to.

,,I waren't able to find much information about similar issues on this forum, which often means that its not that simple.

It would be nice though, I there was a generel rule of thump that said.
In order to make a common 20cm 1200W spot light, it would take a shpere of 20 cm at a multiplier value of 5000 or something along those lines.

Anyways, thanks for explanation on this issue, so far

[Neilg]

dlparisi: It is possible to work it out, but Ive not done it a long time and I dont have any notes from college around anymore.

Its not that hard either, once it's laid out straight with an example of the formula... but I cant find one on the net anywhere. Someone else on here may know.

[lgrohs]

Lux Values

Vray Lights do offer Lux values, but it's listed in the pulldown as Lumens per Square Meter.

[dlparisi]

Not quite. Lux is a measure of how much light is hitting a surface per square meter, not how much a light puts out per square meter. If you use this setting rather than lumens, as you scale the light it gets brighter. Keeping it set at 'Lumens' keeps the intensity the same.

[RErender]

,.i.e., 25". Sorry for the grammar lesson . This is an informal forum after all.

No worries mate. Its always nice to improve a little on my english skills.



Yea, I guess your right about the best way for now is to just crank the multiplier up until the image looks like i want it to.

,,I waren't able to find much information about similar issues on this forum, which often means that its not that simple.

It would be nice though, I there was a generel rule of thump that said.
In order to make a common 20cm 1200W spot light, it would take a shpere of 20 cm at a multiplier value of 5000 or something along those lines.

Anyways, thanks for explanation on this issue, so far

Vlado explains the calc here for a given diameter and wattage http://www.chaosgroup.com/forum/phpB...pic.php?t=9157

Problem is that the wattage that the manufactures list is usually the energy consumption of the bulb not the actual light output, watts vs. watts :P
So to get the wattage of output you need to factor in the efficiency of the light source and the multiplication (focusing), blockage etc. of the fixture.

Lumens are the best (read easiest) in my opinion.

For a quick and dirty conversion you can probably assume 25-35 lumens per watt for the Studio lights, common household incandescents are in the range of 10 - 20 Lumens per watt.