Lighting Spaces – Calculations

[kevinnhatbui]

Hi all and Roger, I have questions on calculating how much light is approximately needed.

I’m currently working through the Look at Lighting section of the website (thank you for having this) and I was curious how you go about approximating the fixtures.

I saw on the Ed Miller’s Death Scenein Assassination of Jesse James, you listed out calculations for 10-14 x 10Ks in a line at 50% spot, and that you had 400 ASA film. You demonstrated some calculations there, but do you have any beginner advice on calculating the fixtures?

From reading so far, you are looking at photometric data on lux/fc of fixtures. I struggle, for example, reading the hospital scene in No Country for Old Men where you had 18Ks shooting from the opposite ceiling over into the high windows.

1. You wanted a specific look, so that is why there is that many shafts of light.

2. You wanted to shoot at F4 minimum at 200 ASA.

3. You had to pivot from the original plan.

How did you calculate the right amount to shoot at F4 at 200 ASA?

Here is a consolidated list of my questions (sorry, I am just starting my journey, so I have not had the opportunity to be on large sets like this):

• How did you calculate the right amount to shoot at F4 at 200 ASA in the hospital scene?
• Was it something you deferred to the gaffer with?
  • or did you draw the diagrams with the fixtures you wanted and then worked it with the gaffer?
• How do you go about calculating the level needed and amount of fixtures needed to light spaces?

Thank you for all the time spent on the articles, I am really enjoying going through them!

 

Topic

[G.C.]

On the one side you can calculate how many foot candles you need to get to middle grey based. A rule of thumb is that you need 100fc for a T2.8 at 100 ISO and 24fps. Double or halve the values for each stop, so T4 at 400 ASA/ISO requires ≈50 fc if you want to light at key.

Lighting units typically have photometric data available, so you know how much light you get at what distance and for a given beam angle.

Each fixture has a different “throw” depending the beam angle. Once you know the beam angle you can also calculate how many lights you need to cover a certain area.

But many decisions also come from experience and instinct, especially with soft lights. How many space lights does one need for a large studio and what’s their spacing? There is no clear cut answer to this.

[LucaM]

G.C. wrote:

On the one side you can calculate how many foot candles you need to get to middle grey based. A rule of thumb is that you need 100fc for a T2.8 at 100 ISO and 24fps. Double or halve the values for each stop, so T4 at 400 ASA/ISO requires ≈50 fc if you want to light at key.

Let me see if i got the math right. You lose 1 stop from T2.8 to T4 but you gain 2 stops from 100 ISO to 400, so at the end you obtained 1 stop more and need half the light (50 fc instead of 100) to have the same exposure. But when keeping the ISO at 100 and going from 2.8 to 4 you’d need 200 fc, is it correct?

[Roger Deakins]

I always make a diagram of how I wish a scene to be lit. Then I discuss the plan with my gaffer and we go from there. If I am uncertain a lamp will give me the required output I will consult a photometric chart but also my gaffer.

[kevinnhatbui]

Thank you for y’alls responses. Really appreciate it! 🙏🏼

[Author]

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