Calculating foot-candles with distance and diffusion

[Ragul]

I understand that for a reference exposure (e.g. T2.8, ISO 100) middle gray is 100 fc, and that diffusion and distance cause light loss in stops.

My confusion is the practical workflow:

When a fixture has photometrics at a reference distance, how do you mentally combine

distance loss (inverse square law) and diffusion loss (1–2 stops)
to estimate the fc that will actually reach the subject?
Do you calculate this backward from the desired fc at subject level, or do you rely more on experience and headroom rather than precise math?

I’d love to understand how you approach this in prep versus on set.

Topic

[Tyler F]

If you know based on data sheet that a unit produces 400fc at 3 meters and you place a diffusion equal to a 1-stop light loss, then you’re working with 200fc.

if you think that’s not enough light to work with, you either need a stronger unit or more units.

It’s better to have more light and be able to dim the unit then to not have enough light and back yourself into a corner

• This reply was modified 21 hours, 36 minutes ago by Tyler F.

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