Measuring Light Output

[Jacob Mitchell]

Hi All!

 

As a student, each projects means a way to stretch myself further. If I'm not trying something new (or a little bit scared) on a project then I feel like I'm not taking steps forward.

 

Lately I've been doing pretty in-depth floor plans and 2D pre-vis, and it has been working wonders for every project. However, I'm still working to get exactly what I want in my head to paper, so that on set my images are not a surprise.

 

Is there a way I can tell how many foot-candles a certain light will output? I'm wanting to essentially know exactly how powerful a light I'll need to expose to a pre-determined f-stop. I'm familiarizing myself with inverse square law, so all I'd need is an output at any one distance and could work from there.

 

Is this just a knowledge gained from experience? Or is there a practical way to determine output?

 

Thanks,

Jake Mitchell

[Jacob Mitchell]

Here's an awesome spreadsheet of different measurements, spot and flood, at 20 feet.

 

http://wolfcrow.com/wp-content/uploads/2014/05/LightingLumensComparison.jpg

Edited September 13, 2016 by Jacob Mitchell

[John E Clark]

Hi All!

 

As a student, each projects means a way to stretch myself further. If I'm not trying something new (or a little bit scared) on a project then I feel like I'm not taking steps forward.

 

Lately I've been doing pretty in-depth floor plans and 2D pre-vis, and it has been working wonders for every project. However, I'm still working to get exactly what I want in my head to paper, so that on set my images are not a surprise.

 

Is there a way I can tell how many foot-candles a certain light will output? I'm wanting to essentially know exactly how powerful a light I'll need to expose to a pre-determined f-stop. I'm familiarizing myself with inverse square law, so all I'd need is an output at any one distance and could work from there.

 

Is this just a knowledge gained from experience? Or is there a practical way to determine output?

 

Thanks,

Jake Mitchell

 

ARRI has an on line calculator and an iPhone App (perhaps a Android one as well...) which lists their light products' output at various distances.

 

The actual lux/footcandles delivered by an arbitrary light depends on a number of factors, reflector shape, lensing if any, etc. Many off brand light producers only list the wattage of the lamp itself, which doesn't directly give 'how much light is falling on the subject'.

 

I'd suggest getting a light meter that reads out lux/fc, and finding a rental house that has a selection of various lights and measure them.

[Adrian Sierkowski]

To be honest; I normally ballpark off of the Arri Estimates for most things-- the issue of moving a light a little closer or using a scrim it in are pretty academic if you ask me. I haven't seen the arri photometrics as an android app, but i did save the page to my homescreen, so i have it whenever (data connectivity permitting).

With time, though, you'll just kinda know.

[Boris Kalaidjiev]

Are there any other Apps out there apart from the Arri Photometrics that give you photometrics for all the rest of the lights(jokers, kinos, dinos, LEDs...?

Thanks!

[Stephen Sanchez]

You're looking for photometrics. Most big companies, even Aputure, have photometric documents that display a fixtures intensity measured at various distances and their beam angle.

That, plus knowing the stop loss of your diffusions will help find the stop you'll get.

As practical advice, if you can afford it, try to always have more fixture wattage than you need. You can always remove light, but you cant get more if you need it.

[Boris Kalaidjiev]

10 hours ago, Stephen Sanchez said:

You're looking for photometrics. Most big companies, even Aputure, have photometric documents that display a fixtures intensity measured at various distances and their beam angle.

That, plus knowing the stop loss of your diffusions will help find the stop you'll get.

As practical advice, if you can afford it, try to always have more fixture wattage than you need. You can always remove light, but you cant get more if you need it.

I was just wondering if there is a document, App or something where you can find all the data of the various brands and types of lights in one place instead of digging around all the manufacturers documents. 

[Stephen Sanchez]

Not that I know of. Arri has their own app as mentioned. I've had to search the web for each fixture.

It takes a minute to compare, too. Because not every manufacturer measures intensity at the same distances. So then you have to do conversions.

[Frank Wylie]

Spectra Cine Professional light meters (the old ones) are relatively cheap on the used market and they have direct foot candle readout.

Of course, this is the cat's meow:  http://www.spectracine.com/product_2.html

 

[Johanan Pandone]

I have a sekonic 398 and I'm tired of doing ratios in my head. That spectra looks awesome. Any other reccomendations?

On 9/2/2021 at 7:16 AM, Frank Wylie said:

Spectra Cine Professional light meters (the old ones) are relatively cheap on the used market and they have direct foot candle readout.

Of course, this is the cat's meow:  http://www.spectracine.com/product_2.html