A Process for Designing Lighting for the Stage: Determining Lighting Areas (Part 3)

Once the Lighting designer understands the beam properties of the available fixtures, has a plan (in the form of  having a lighting key) and has a firm understanding of the theatre architecture and available lighting positions, then he or she needs to determine the throw distance from the lighting areas to the spots on stage.

Lighting Key for production of Prima Donna

Remembering the lighting key that we looked at for the production of Prima Donna, we can begin to determine the throw distances from the lighting positions.

For example:  Let’s begin by planning the light coming into the lighting areas from Stage Left as a 45 degree front light (labeled “Neutral Bounce Light in the key).

Plan View showing the throw of a 45 degree SL front light

The drawing to the left shows a plan view of a portion of the stage with a figure standing on the center line just a couple of feet upstage of the plaster line.    A young designer looking at this plan would be excused for believing that it shows a throw distance of  28 1/2′ from the lighting instrument to the figure.  However, that is far shorter than the actual throw distance.  What is not accounted for in the plan view is the elevation of the fixture above the stage which increases the throw distance.

Section View of the stage through the center line

The diagram to the right shows  the section through the center line.  Notice that the section view shows that the lighting area is calculated at the actor’s face level (from 5′ to 6′ above the stage floor) to account for the fact that providing illumination so that the audience can see the actor’s face and features is one of the main goals of the Lighting Designer.  Again, a young designer might be excused for thinking that this diagram suggests that the throw distance from the fixture to the figure is 33′.  However, once again, that is not an accurate assessment.  This while the section view does accurately describe the elevation of the fixture, it does not account for the angle that the instrument is placed with respect to the center line.

Section View drawn along the axis of the lighting angle

In order to account for both elevation and angle in calculating the throw distance the designer might create a section drawing through the axis of the throw of the lighting fixture.    Such a section drawing at left shows that the throw from the chosen position should be in the range of 37′-8″.

Using the information from the preceding post, we can determine that a 19 degree Source Four fixture positioned as shown on the first beam position (with a Multiplication Factor of 0.31  will project a lighting area at face level of 11 1/2′ diameter centered upon the figure.  Notice also that if the lighting area moves up or down stage, then the throw distance would change and the diameter of the lighting area would become larger (if the throw distance increases) or smaller (if the throw distance decreases.)

That’s enough for now! Have fun!  Be safe!

SJM

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