Foot Candles: the best way to gauge light
- May 22, 2020
- Chris Team HV
When you’re taking meter readings on a scout and you’re trying to figure out how many fixtures you need to get your desired stop, what are you using to look at lights? foot candles/photo metrics?
First of all, experience is absolutely everything! You can go through all of the lessons, all of the courses and film school and they will give you a good basis (Hurlbut Academy will give you an excellent basis, but I’m biased). However, ultimately by doing, by making mistakes and by learning from them, you’re going to get better. Make more mistakes – learn more – get better – repeat.
The best DPs in the world have got to where they have through constantly experimenting with what light works where and when and having their light meters ready to figure out how.
You have to do two things:
- Work out the intensity of light you require
- Find the right light fixtures and work out the right distance that will provide that intensity.
I go on foot candles, that’s the best way to gauge light. Most of the manufacturers when you’re looking at their spec sheets have it measured in foot candles (FC).
Foot-candles are the unit of measurement for light intensity (or illuminance). Remember this: one foot-candle is the illuminance produced by a standard candle that is one foot away from the Subject.
Illuminance is the measurement of light reaching the subject not the light reflected from it (which is called luminance). Illuminance can also be measured in the SI unit of Lux.
Mole Richardson created this awesome, monster book with specs in it and as a gaffer, that was one of the first things I bought. I remember walking into the Mole Richardson store and buying this thing that’s literally four inches thick!
It had tons of pictures and detailed specs and in the “illumination tables” it shows what light intensity you’re going to get at 10 feet away, 100 feet away and 150 feet away. It’s one of the things I used religiously!
When I walk into a room that has beautiful exposure, my light meter is straight out, I’m recording the Foot Candle and I’m doing my calculations for what I need to do to emulate it. Then it’s in the memory bank for the rest of your career!
As much as I love to teach and as much as you can learn from me at Hurlbut Academy (biased but true), as DPs, we are creatives and we are scientists. We have to experiment so we can do with light what Chefs do with food and Artists do with paint. We have to constantly be creating recipes while learning the techniques to make them better.
When I was a Gaffer, I learned everything I possibly could from my mentors Herb Ritts, Daniel Pearl and Kevin Kerslake. Throughout the commercials, the photo shoots and the music videos that I did with them, I was a sponge, soaking in every set up and building that experience so I knew what units worked best.
In 2009 (just over a decade ago) when I was brought onto Terminator Salvation, the Director McG said, “we’re going to light 50 acres, and these two characters are gonna have to run almost a mile through this minefield!” I was like, “Whoa, what am I gonna use to light that?”
So I went to my Mole Richardson book again. I opened up the 24 light Dino, and I started to do calculations with foot candles…
What I figured out, is that if I put two 24 light dinos into a Condor that was over 450 feet away, I was going to get my 1.5 as my backlight.
Additionally, I always like my backlight to be a stop and a half below my key. If I’m exposing at a 2 then a 1.5 is absolutely perfect for a backlight on a moonlit night.
What I use:
These are the things that you can do using those foot candles. You’re able to go to your meter and measure it all out. Be careful though, because there’s only a few meters that do this.
The Spectra is is one of them.
How I use it:
- Set the Spectra to Foot Candles (FC) on a button. You can meter it in lux, but I want to meter in foot candles.
- Take a look at what I’m seeing –
I’m loving the light on my face. I love how, in the room, you’re seeing darkness around me. Then this light is coming through the window and it’s balanced to the background!
3. I meter it – it’s 92 foot candles.
4. Because I’m using ND, I’m going to change the ISO to 800.
5. That’s basically measuring an 8 (T-stop) on my face.
6. So, I need to have a light that’s going to be able to emulate that soft light I have coming through here for it to be an 8 (because that is going to be 92 foot candles).
7. So now the game I play is “what light can I bounce off something to recreate what is happening right here? What can I bounce off to give me this beautiful soft light on my face? How can I emulate that and get exactly 92 foot candles?” (It’s not exactly Heads Up with the whole family, but it’s a fun game if you love cinematography!).
This is what I do all the time! Lydia’s constantly like “what are you doing with that light meter?” because I’ll see something, I’ll meter it and then I’ll see how many foot candles it is!
These are the kind of things that you want to be doing to continue to explore and educate yourself. I’m bringing experience like above and more that I have gained from my mentors (who gained it from many many others) so that you can propel yourselves forward, train your eye, can understand what the measurements are, read a spec page and develop your own recipe book.