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Course: THEA 272 Stagecraft

Stage Lighting Produciton (for 4/29/99)

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Color in Light

• Primaries in light (RGB)
• Additive and subtractive mixing
  • What happens with a pure blue filter on a red object?
  • What happens with a pure red filter on a pure blue light?

Color vocabulary

• Hue, value, saturation (chroma, intensity)
• Tint, shade, tone, primary, secondary, complementary
• Warm and cool
  • Why put one color on one side and a different one on the other?

"The Equation":

• P = IE or W = VA (West Virginia formula)
• Most of the time you need to compute amps.
• A = W/V or 20a = 2400w/120v.
• Problems: 2 500-watt instruments. How many amps?

Lamps, reflectors, lenses

Basic Instrument: 3 parts

1. Lamp and socket: Provides illumination
2. Reflector: Directs the illumination
3. Lens: Focuses the illumination

Lamps:

Types:

1. Incandescent
2. Tungsten-Halogen, or quartz
3. Gas tube (flourescent - arc technology)

Technology of each type

• Incandescent:
• molecules leave filament and are deposited on glass envelope;
• heat dissipation within envelope is critical.
• Tungsten-halogen:
• molecules leave filament, combine with halogen gas, and redeposit back on filament;
• heat dissipation within is not critical, smaller envelope possible,
• filament tends to be more fragile when hot,
• finger oils on envelope will distort glass when heated.

Lamp shapes and bases

Reflectors:

Types of reflection:

1. Specular: mirror-like, duplicates angle of incidence, preferred in most lighting equipment.
2. Diffuse: reflects light in multiple directions, for soft focus situations.

Types of reflectors:

1. Spherical: single focal point, diverse beam if lamp is at focal point, beam is variable by lamp placement in relation to the focal point.
2. Parabolic: single focal point, lamp at focal point produces parallel beam in single direction.
3. Ellipsoidal: two focal points, lamp at one sends all beams through second; if second is at focal point of lens it enhances efficiency, creates option of a gate which can be used to shape beam.

Lenses:

Technology

• Light bends around edges of objects
• Light bends as it passes through a surface, relates to change in the speed of light in a material.
• Lens has focal point at which parallel rays through a lens from convex side will converge. Light source at focal point will produce parallel beam.
• Focal length of lens depends upon curvature of convex side.
• Tight curvature (small diameter) requires thicker glass. Thick glass in center heats more slowly than thin glass at edges, resulting in cracks.

Types:

• Plano-convex: Standard lens with 1 flat side and 1 convex side. Often found cracked if very large.
• Fresnel: Cuts away glass on convex side, retaining curvature in steps. Flat side has "pebbled" surface to diffuse light and eliminate rings from curvature steps.
• Step lens: Cuts away glass on the flat side in steps. Sometimes problems with step rings.

Beam and field:

• Instrument focus traditionally indicated by [lense diameter] x [focal length], both in inches.
• Newer approach uses beam and field angles, specified in degrees of spread. Necessary because newer instruments use lenses differently.

Parts of the lighting instrument:

1. Housing or hood
2. Reflector
3. Lamp
4. Socket
5. Lens(es)
6. Filter holder
7. Shutters or iris
8. Pipe clamp
9. Yoke
10. Safety chain

Instrument types:

Floods:

• ERF or Scoop:
• No lens
• diffuse relfector
• Ellipsoidal reflector
• No built-in filter holder
• Aim rather than focus.
• Use: wide-spread, unfocused light; general illumination: worklights, drop washes. Heavily used in video, film, still photography.
• Strip lights:
• No lens
• diffuse reflector, if any
• multiple circuits for multiple colors
• permanent color media (rondels)
• Aim rather than focus.
• Use: Border strips, foot lights, drop washes with color changes.
• Beam Projector:
• No lens
• spherical reflector
• Lamp baffle
• Aim rather than focus.
• Use: strong parallel beam - intended to be intense: replicate sunlight through windows and in limited areas; more modern equipment is more efficient and lighter.
• Par Can:
• Instrument has no lens or reflector. Lamp is self contained filament, lens, reflector.
• Limited focusing capacity, very evident hot spot.
• Lamps are sealed beam PARs; available in wide, medium, narrow; orientation of filament may be rotated.
• Use: controlled general illumination, usually in multiples: bright stage washes, punches.
• MR16s are miniature versions of the PAR can.
• Fresnel:
• Lens stepped on curvature with diffusion on flat side.
• Spherical reflector
• Use: Soft edge, moderate intensity beam; focus limited to size of hot spot (flood or spot positions): soft directional lighting, fills, toplights and backlights.

Profiles:

• ERS or Leko:
• 1 or mor lenses, available in a variety of beam spreads.
• Ellipsoidal reflector
• Shutters or iris, pattern slot.
• Newer versions have more adjustments including joystick lamp positioning, zoom controls for variable beamspread.
• Use: Highly focusable, crisp beam which may be softened: primary general use stage lighting luminary.
• Source 4 (ETC) and Shakespeare (Altman)
  • very similar technologies and beam characteristics as above, but with improvements in light efficiency and operation.
• Follow spot:
• Multiple lenses
• Internal color frames
• Very high intensity lamps
• Beam shaping and management controls
• Use: continuous operator control, moving beam of light as needed during performance.

New Technology instruments

• VariLites, RoboScan, other moving fixtures
• Lasers

Other parts:

• Tophat or snoot
• Barn doors
• Used toconfine spill and hide front lens, especially on fresnels.
• Pattern or Gobo
• Shadow pattern projected by instrument from template in gate.
• Donut
• Round opening for pattern slot that sharpens pattern focus.
• Also: color frames, color scrollers.

Dimmers:

Resistance

• Establishes variable resistance in a cercuit by tapping current from points in a resistacne coil.
• Problems: Load is directly related to resistance; removing or adding lights will change the light brilliance. Current not used is dissipated in heat. Power curve is not in harmony with handle position.

Auto-transformer

• A second current is used to modulate the main current; by varying the applied current, only the amount of current needed is consumed.
• Load is unrelated to control method
• Power curve is more direct in harmony with handle position.
• Mastering possible by ganging (mechanical), electrical mastering within limits (low capacities).
• Heavy and large.

Silenium Controled Rectifier (SCR)

• Uses miniscule current to control a large current.
• Permits miniaturization of current in dimming control and miniaturizaton of controls.
• Permits unlimited electrical mastering due to amount of current involved.
• Permits multiple alternate sets of controls.
• Permits separation of control and dimmer.
• Poor systems subject to ghosting, current fluctuations, instrument buzz and hum, more care in connection unless shielded (can’t be plugged hot)

Controllers:

• Multi-scene preset
• Electronic/computer

Hang sequence

1. Place clamp on pipe and finger-tighten.
2. Pull all shutters out of beam.
3. Check adjustments for freedom, including barrell.
4. Generally orient instrument (US, DS, SL, SR)
5. Snug all adjustments with wrench.
6. Tighten pipe clamp one-quarter turn.
7. Attach safety chain.
8. Let connector dangle until position is cabled.
9. Reweight line as needed (typcially every 4-6 instruments)

Cable sequence:

1. Plug all connectors at position to nearest outlet, or as plotted.
2. Cable and jumper to more distant outlets.
3. Tie cable socket end to pipe at instrument clamp. USE BOW KNOT.
4. Plug remaining instrumetns.
5. If there are more instruments than sockets, consult plot to determine which instruments will run together.
6. Note all instrument circuits on paperwork.
7. Test patch entire position and power up everything.
8. Correct ALL problems: lamps, shutters, cables, focus freedom, etc.
9. Pick up and dress cable:
10. Coil excess cable at the plug location.
11. Bundle cable lines, lift to pipe, and tie at appropriate intervals. USE BOW KNOTS.
12. Fly electric out to spike.

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