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By the Numbers Photometries
The job of cinematography requires a lot of planning. When will you shoot? What kind of coverage will it be? What is the location like? How long will a particular scene take? What equipment is needed?
Sometimes the requirements for types of camera equipment are quite simple to determine. Smooth camera movement requires a dolly or stabilizer of some kind. Crane moves require, well, a crane (or jib). The requirements for lighting, however, can be a bit confounding to young cinematographers - how can I figure out what lights I need?
There's a lot to choose from! But being able to plan your lighting requirements ahead of time requires an understanding of photometries, and some experience. Many lighting manufacturers present photometries, in their literature or on their websites, in the form of charts listing the various intensities of light that will be output from a specific fixture at a given distance. Armed with this information, you can calculate the /-stop you need for a particular shot or sequence and calculate the type of instrument you'll need to achieve that stop. These are the first steps to planning your lighting.
In the U.S., working with our imperial system of measurement, most lighting companies will present their photometries in footcandles (fc). Afootcandle is the theoretical light emitted from one candle from 1' away. In many other countries, they refer to the basic unit of light measurement as the lux, which could also be thought of as the "meter-candle." One lux is the light from one candle 1 meter away. One footcandle is equal to 10.764 lux, or 1 lux is 0.093 footcandles.
Footcandles are a measurement of incident light - that is, the light that is falling onto an object. After the light strikes the object and reflects off of it (this is the light that we can see), we then measure the intensity in footlamberts (fl). Both units of measure are referring to intensity of light; footcandles is a measurement of the light emitted from the source, and footlamberts is the light reflected off of the subject.
Due to the property of physics known as the inverse square law, light will diminish in intensity by the square of the distance traveled from...