From time to time, stagehands need to be able to read a light plot. For most shows this skill is not needed; the show carries its own lighting setup and the show lighting director or electrician deals with the proper locating of the instruments to be used. For some shows, however, a company will choose to use house-owned or locally obtained instruments, and an advance light plot will be sent ahead. In these cases, it falls to the local technical director or Union electrician to do a pre-hang of the plot, so that it is ready when the company arrives. For this reason, it is a good idea for stagehands to have some familiarity with plots.
First, some definitions. Technically, a light plot is the entire package of instructions for hanging and focusing the lighting for a show. These may include some combination of the following: a light plan, a lighting section, instrument schedules, hookup schedules, dimmer schedules, cue sheets, focus charts, equipment shop orders, color cut lists, and "cheat sheets". Of these, the local electricians will typically receive only a light plan, and sometimes the instrument schedules and cue sheets. Equipment orders may also be supplied, but are often generated by the electrician from the plan.
A Light plan is the top view of the stage, showing the stage house itself, the scenery and masking, the hanging positions for electrics, and the location of the lighting instruments on the various positions. There should be enough information provided about each instrument in terms of type, unit number, color, dimmer or control channel, and ancillary attachments so that the show could if necessary be hung just from this piece of paper.
Schedules are lists of information about the instruments collated in different ways. Instrument schedules are organized by instrument location and unit number. Instruments may be numbered consecutively throughout the entire theatre, from F.O.H. to far upstage, but the more common system in professional theatre is to start over at #1 in each new hanging position, e.g. 1st Electric #1. Hookups are organized according to control channel and list circuits in each, with attached information on the instruments plugged into each circuit. Cue sheets list the levels of dimmers or channel in each cue, and may be sent ahead to be entered into the house computer light board. Focus cards are used mostly by the show electrician, and contain information on where and how each dimmer is focused. Equipment shop orders are used to order equipment from a rental house if the theatre doesn't own enough equipment for the show. Color cut lists are often locally generated to match the available equipment. Cheat sheets are used mostly by the lighting designer or director to help find specific dimmers during level setting sessions.
A light plan is the most important part of a light plot. As previously stated, a properly done plan should contain all information needed to successfully hang a light plot. The attached schedules are mainly to make finding information on the plan easier. All plans have some combination of semi-standardized features. The United States Institute of Theatre Technology (U.S.I.T.T.) has made some attempt at standardizing plots, but designers are an unruly and pretentious lot who are all convinced that their way is best and the rest of the world be hanged! (All right, so I am one, too.) Anyway, U.S.I.T.T. has made only limited headway, so don't be surprised at the amount of variation between light plots.
Title block- this is usually located in the lower right corner, and contains show name, producing company, designer, director, date drawn, drawing number in series, theatre, etc. The most important piece of data to the electrician in the drawing scale, e.g. 1/4 inch = 1'-0". This bit of information allows you to measure the location of drawing features so you know where to put them on stage.
Instrument key- located near the title block. On a drawing, it is standard practice to delineate type, size, and focal length of instruments using semi-standardized symbols, usually drawn using a template. The standard American symbols and markings are shown here, as adopted by U.S.I.T.T. and most working designers. There are several common variations, plus those generated by CAD programs, and several European symbol systems. With all those possibilities, the designer must include a key to interpreting the symbols used on the particular plot at hand.
Data key- located near or as part of the instrument key, this key guides the electrician in interpreting the data provided about a particular instrument, in terms of number, color, area of focus, control circuit, etc. U.S.I.T.T. has adopted a standard for this as well, but many, myself included, do not use the standard exactly as published. Check the data key to properly interpret all the numbers written around and in the instrument symbol.
The Plan- finally, the actual drawing itself. Hopefully, it has been drawn in scale so that the electrician can lift measurements from the drawing using a scale rule. Many designers also include a measuring scale as part of the drawing, for instance, by scaling the Plaster Line (PL) to facilitate estimating the position of instruments on the electrics pipes. If this has not been done, the electrician should do this first thing to speed up drawing interpretation.
Another feature to note is the Line plot, placed wherever the flying rail is located on the drawing; this lists line assignments and, ideally, trim heights for electrics, flown scenery, masking, etc. The exact line placements for electrics should be coordinated with the head flyman and/or head carpenter.
On each pipe designated as an Electric will be symbols for each instrument to be hung, with associated color, area of focus, gobo, channel assignment, etc. for each. Check the key for interpretation. The designer may also indicate potential two-fering possibilities, or you may need to check the channel assignments for these.
Another special feature to look at is the drawing of the Cove positions. The location of these positions, as well as of boom positions, are shown using a top view, but this does not give details of the number and vertical positions of the instruments on the cove and boom pipes. This information is shown with a removed view. A removed view is a view included with an orientation other than the main drawing. In this case the removed view is a side view of the coves included on what is otherwise a top view of the theatre.
Another feature to note is the Beam. A primary assumption when reading plans is that all items are in scale on the drawing and in relation to each other. The beam position (the position in the ceiling over the audience) is sometimes an exception. Beams are often a long way from the front of the stage, and their position may be truncated (foreshortened) on the drawing to make the drawing more compact and easy to handle. This is usually indicated with a truncated dimension line giving the actual measurement. A rule of thumb in the theatre is that objects are numbered from the plaster line (the proscenium opening) and the center line; therefore, just as the batten closest to the proscenium is Pipe #1, and the numbers increase as you move upstage, so the beam closest to the stage in a theatre with multiple beam positions (like Pickard) is Beam #1, and the next out is Beam #2, etc.
Another rule of thumb: a sort of standard is that lighting instruments should be located no closer than 18 inches apart, measured C-clamp to C-clamp. While this is an often violated rule, if you can adjust the instruments slightly to provide his clearance, it will make focusing easier. Also, when cabling instruments, have you electricians tie the female connectors right next to the instrument's C-clamp, then plug it in, rather than stretching the instrument's pigtail to reach the cable. Again, this will make focusing easier.
I have also included is a Section view. It is more a tool of the designer than of the electrician, but it is included in case you ever run into one. A section is a side view of the theatre space, usually taken through the center line. It shows the vertical measurement of the electrics and other features, and is used to determine trim heights and lighting angles in relation to acting areas. Note that the lighting area centers, indicated in position on the light plan, are shown as actually being about five feet off the floor on the section view. This is because lighting faces is the most important function of theatre lighting. This is important to remember when facing the more difficult tasks of the electrician, i.e. modifying light plots.
The light plot received as part of an advance plot is usually a fairly generic, idealized notion of what is required for the show. Theatres, however, vary widely in design, size, and appointments. It often happens that the designer has placed lights in places where there are no hanging positions in the real theatre. It is always best to place instruments as closely as possible to their indicated positions, but you may have to give freely interpreted approximations, for instance, placing balcony rail instruments in the beams of a theatre that has no balcony rail. Remember that it is faces you are lighting, not floors, and that lights focused on the face about 45 degrees up will light faces better than top or near top lighting.
You may also have to do some instrument substitution. Try to learn the beam characteristics of common lighting instruments. Then, if you must substitute, pick instruments with similar beam types. A Fresnel is a poor substitute for an Ellipsoidal, but may work for a wide beam PAR can. A narrow beam PAR may substitute for a long throw Ellipsoidal from a beam position if the beam spread is similar and the oval pattern and increased spill from the PAR can be controlled or tolerated. Scoops and strip lights are interchangeable for cyc and drop lighting, if the color is matched. These are things best learned by working with lighting instruments, so take the opportunity to do so whenever possible.