March 20, 2005

Choosing the Right Lights for Your Set
Using Illumination Tables

experience level: intermediate - focuses on a specific filmmaking craft

Summary

A photographer may match light fixtures to recording media (including film emulsions and video camera chip-sets) by comparing manufacturer illumination tables, readily available on the net.

The Lighting Challenge

After I have been lighting for a specific camera or film stock for awhile, selecting instruments to light my scenes becomes second nature.  I have a sense memory of their look, feel, and illumination characteristics that gets me ninety percent through my lighting setup.  After that, I can use my meters and/or video monitoring to fine tune the scene.

But what if you are new to lighting a set?  Or, what if you are considering a light you have never used?  How do you select the right light for the job?  Visual character aside, how do you assure there will be enough light to properly expose the film emulsion or video chip?

There are many elements that may be used to alter the character and amount of light striking a set, subject, and ultimately, a recording medium.  These tools interact in a complex but quantifiable way to create an image.

many tools affect the exposure of the recording medium

A director of photography has a masterful command of all of these lighting tools and can use them to interpret the needs of the project and the creative imagery that results.  Of course, the use of each and every one of these elements affects the photographer's choice of lighting instruments.

The Scope of This Article

For the purposes of this article, I am going to focus on the simplest possible lighting scenario.  I will be addressing the subject of illumination only.  While color is certainly an important aspect of lighting, we must understand illumination before we can predictably alter the color characteristics of our imagery.

In simplest terms, light from a light source, bounces off a subject
and through the lens to expose a recording medium.

The elements used in this simplest of lighting/exposure scenario are:

• light instrument (measured in foot-candles)

• subject - 18% grey card - a fixed measuring reference

• lens aperture (measured in f-stops)

• exposure time (measured in seconds)

• camera/film exposure index (measured in ASA rating)

in simplest form, light from a source bounces off a subject and passes through a lens to expose a recording medium

What are We Controlling?

Ultimately, a director of photography is controlling exposure.  In our simplified scenario, a light source, lens aperture, camera shutter speed, and recording medium exposure index are manipulated in order to record an 18% grey card at the middle of the emulsion or video chip.  (The 18% grey card renders a middle grey since light is measured logarithmically.)

A director of photography starts his lighting plan by locking down one or more of these elements in order to choose the others.  For instance:

• f-stop - You might wish to shoot a project at or near a specific f-stop in order to achieve a certain depth-of-field or because the lens looks better at certain apertures.  You may then choose a light source, shutter speed, and exposure index to achieve proper exposure of your recording medium.
   

• exposure index - Perhaps a specific video camera or film stock is desirable to achieve a certain creative look.  Such choice of camera or stock results in a fixed speed (or in the case of video camera, range of speeds) at which it exposes.  You may choose a light source, shutter speed, and f-stop to suit.
   

• foot-candles - If you are shooting with available light like the sun or in a sensitive public building that does not allow large cine-lights, you may be confined to a specific range of illumination.  You may choose an f-stop, shutter speed, and exposure index to achieve proper exposure.

The photographer may also choose to lock down more than one element, further reducing the choices in the remaining elements.  For instance, by default, a film camera exposes an emulsion at 1/48th second per frame.  If the photographer also desires a specific depth of field for a shot, she may also lock down the f-stop.  With those two variables established as constants, the choice of light source and emulsion exposure index becomes simpler (and more limited.)

Wherever you start your lighting plan, the remaining elements may be chosen using a quick and concise tool:

manufacturer's illumination tables.

A Brief Glance at the Math

There are all manner of mathematical formulae that describe the relationship between foot-candles, f-stops, exposure time, and exposure index, like the one below:

But, I didn't become a visual artist so I could use mathematical arcana on a daily basis.  Fortunately, I have the tool that allows me to avoid math altogether:

manufacturer's illumination tables.
 

Practical Use of Illumination Tables

Manufacturers of professional lighting gear, film, and cameras provide illumination tables that describe how their products deliver, or react to, light.  These tables are almost universally quantified in foot-candles (or Lux for metric regions.)  If we assume the following general relationship;

we may quickly determine if a lighting instrument will be sufficient (even ideal) to light a scene for our video chip or film emulsion.  One need only compare the illumination table of light source and recording medium to determine if they are compatible.  (In reality, this comparison is further complicated by the introduction of filters, gels, diffusion, costumes, sets, actor's skin tones, creative choices, etc. but we're keeping it simple here.)

Very often, low-budget filmmakers are, first, constrained by their choice of camera or film-stock.  Given that common constraint, let us explore two lighting scenarios that start with locking down the variables in the camera and recording medium.  We'll take a look at;

Kodak 7279 500ASA film

and the

Canon XL-2.

forward to Example 1: Kodak 7279 500ASA film

Take a look at the following light instruments.  Each page includes illumination tables to assist you in choosing the right light for your project.

click on a light to learn more about the instrument