What are theatrical lights?

There are four types of theatrical lights- conventional lights, LEDs, intelligent moving lights and special effects.  Most schools and churches use conventional lights, but more and more are starting to use LEDs and moving lights.  This post will focus on conventional lighting.  We will cover the others at a later date.

Conventional lights are made up of four parts- the body, the lamp (or light bulb), the lens train and the reflector. 

·         The body is the shell that holds all the other parts.  These are usually made of metal and are designed to protect the rest of the parts and to channel heat. 

·         The lamp is what puts out light.  There are a variety of lamp styles and sizes.  Each has been specifically designed to function best in a particular light.  Lamps are generally not interchangeable (except for changes in wattage).  They go by the ANSI code stamped on the base of the lamp (HPL, HTI, BTL, etc).  This is handy information to have, so making a list of what types of lamps you use will make reordering easier. 

An HPL 575 lamp

·         The lenses redirect and shape the light, much like how lenses in a pair of glasses work.  Lens types are particular to the type of fixture.  Lenses are made of glass or Pyrex. 

 A double plano-convex lens

·        The reflector redirects the light from the lamp forward through the lenses.  Reflectors come in three shapes (elliptical, spherical, parabolic) and are made of metal or glass.

A Source Four ellipsoidal cold mirror reflector

There are three main forms of conventional lights.  Ellipsoidals (sometimes called Lekos, ERS or Source Fours) are long and skinny and use an elliptically shaped reflector.  The lamp sits at the back of the fixture and pokes through the reflector.  There can be either one or two plano-convex lenses inside the body.  A plano-convex lens is flat on one side and curved on the other.  These lenses are positioned in a certain relationship to each other in order to create a certain angle of beam spread (how wide the light is when it comes out the end of the fixture).  

These lenses mean that an ellipsoidal can be sharply focused.  It is the only conventional fixture that can hold a sharp focus.  Thus it is the only fixture that can use gobos (gobos are a piece of metal with a pattern stamped out of it, allowing light to be projected in an image.).

 A breakup gobo projected on the floor.

Assorted custom and standard gobos

Ellipsoidals have metal shutters on all four sides.  By pushing these shutters in and out you can block light from certain areas onstage.  You can also shape the light into squares, rectangles and triangles (or perhaps a parallelogram if you are feeling feisty).

A company named ETC makes a fixture called a Source Four ellipsoidal.  Calling an ellipsoidal a Source Four is tricky though because ETC makes a Source Four par, a Source Four parnel and a Source Four fresnel.  Many people persist in calling the ellipsoidal the “Source Four” though so it has kind of stuck.  The Source Four ellipsoidal was a unique fixture when it first came out.  It uses a dichroic coating on a glass reflector.  This dichroic coating reflects the visible light energy to the front towards the lenses while allowing the heat energy to pass through.  This means the front of the fixture stays cool to the touch.  Before ETC began using this technology it was impossible to touch the front of an ellipsoidal without getting burned.  A technician had to use thick leather gloves and even then would eventually burn through the leather.  Now a technician can manipulate the end of the fixture without gloves.  It gets warm, but not hot.  (The back of the fixture still gets really hot and care should be taken when working back there.)  This dissipation of heat allowed for all sorts of new accessories.  We now can use glass gobos, gobo rotators and reel rotators without fear of them burning or breaking from the heat.

The other innovation developed by ETC was the rotating shutter barrel.  By loosening a knob at the front end of the fixture the technician can rotate the end of the fixture and the shutters in order to make those difficult shutter cuts. 

Source Four fixtures come in a variety of lens degrees (5, 10, 14, 19, 26, 36, 50, 70, 90 degrees).  This variety allows a designer to pick exactly the right light for the need.  ETC very cleverly designed the Source Four ellipsoidal so that these lens tubes are interchangeable.  This allows for you to have a set inventory of bodies and an extra inventory of different lens tube degrees.  This makes your ellipsoidal inventory very flexible.

While ETC is certainly the leader in the ellipsoidal field, Strand and Altman also make similar ellipsoidal fixtures with similar attributes.  Be aware that all ellipsoidals are not created equal though and care should be taken before purchasing new fixtures.  Cheaper isn’t always best.

There are many accessories for ellipsoidals.  Gobos made of metal or glass will fit in the gobo slot or the accessory slot at the shutters.  Gobos throw patterns on the stage.  Gobo rotators (like the GAM Twinspin or the Apollo SmartMove) are units that spin patterns around a central focus point.  A GAM FilmFx uses a pattern reel so there is no central focus spot.  It provides a continuous flowing pattern.  Iris kits fit into the accessory slot and allow you to iris down the size of the pool of light. Top hats fit in the gel frame holder and are used to prevent the spill of light.  Scrollers fit in the gel frame slot and allow you to do multiple colors in one fixture.  There are many more accessory options that allow you to turn the ellipsoidal into a followspot, a moving light or a gobo changer.  More accessories are developed every year!

The ellipsoidal is the workhorse of the theatre.  As a lighting designer, I use more of these than anything else.  It works for front light, side light with pattern and specials.  They are the most expensive of the conventional lights, but still very affordable.  Check out the links for ETC, Altman and Strand at the right for more information about their ellipsoidals.  We have a gazillion of these in our rental inventory as well if you would like to just try them out for a show or special project.

Coming up next- fresnels!