FRESNELS
The Fresnel (pronouncedfreNEL) is one of the most flexible fixtures to work with, being designed to create a relatively wide, even field of light with adjustable intensity and field size. The light from a Fresnel makes clean, hard shadows. Its clean beam makes it a good choice for lighting actors’ faces, either directly or through diffusion. For these reasons, it is the most commonly used fixture in film and television (Figure 3.2). Figure 3.3 illustrates some Fresnel fixtures that every electrician should be able to identify.
The light is named for its Fresnel lens, which refracts the diverging rays of light emitted by the bulb into a controlled beam of light. The Fresnel lens has the same light-bending characteristics as a standard plano-convex lens, but the Fresnel’s design compresses the convex curve into jagged steps (Figure 3.4), making it lighter and thinner, so that it retains less heat. The back of a Fresnel lens is frosted or slightly pebbled. This helps maintain a very even beam, and prevents the lens from actu- ally projecting an image of the filament of the lamp.
Equally important, the fixture uses a spherical reflector. The reflector is really what gives the light its high level of control and even field characteristics, because the geometry of the reflector is such that light reflects straight back through the bulb (Figure 3.5). All light therefore emanates from a single point within the fixture (the filament), which is what allows the Fresnel lens to control the beam so cleanly. Some manufacturers utilize a polished reflector, which maximizes light output, and others use a slightly frosted reflector, which helps maintain a very even field of light.
FIGURE 3.2
Anatomy of a Fresnel fixture.
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Fresnels
Baby 1,000W Type 407 Junior 2,000W Type 412 Senior 5,000W Type 415 Tener 10,000W Type 416
Big Eye Tener 10,000W Type 4241 Baby-baby 1,000W Type 2831 Tiny-Mole 200W Type 2901 Inbetweenie 200W Type 3101 Pepper 100W/200W Pepper 200W Pepper 300W Pepper 420W Pepper 650W Pepper 500W/1k Betweenie 300W Type 3131 Tweenie 650W Type 4821 Baby 1,000W Type 3081 8 Junior 2,000W Type 5291 Mini-Mole 200W Type 2801 Midget 200W Type 2351 Baby-Junior 2,000W Type 4131 Baby-Senior 5,000W Type 4191 Baby-Tener 10,000W Type 4181 20k 20,000W Type 4251 FIGURE 3.3
Fresnel fixtures come is all sizes from tiny 100 W fixtures to huge 20k fixtures. Note that our industry commonly refers to lights by there wattage as 1k, 2k, 5k, and so on. When we use the letter k, it really means kW. A 1k is a 1 kW or 1 kilowatt (1000 W) light.
(Courtesy Mole-Richardson Company and LTM Corporation.)
Inside the housing, the globe and spherical reflector are mounted together and can be moved toward or away from the lens by an exterior adjustment knob. Moving the globe and reflector toward the lensfloods the beam, increasing its spread and decreasing its intensity (Figure 3.5A bottom). Moving the globe and reflector away from the lensspots the beam, making it narrower and more intense (Figure 3.5A top). The adjustable focus makes it quick and easy to obtain the desired intensity or beam width.
Fresnel beam
To anticipate how the light will behave when an actor walks through it, it is helpful to have a three-dimensional mental picture of the beam’s shape and intensity, the manner in which intensity falls off toward the edges, and how varying the amount of spot or flood changes these characteris- tics. Figure 3.6 illustrates the terms field and beam, terms used in describing the photometric2 qualities of a fixture. A polar distribution graph (Figure 3.7) gives a clear picture of the “shape” of the beam intensity and how it changes from flood to spot.
At full flood, the beam is relatively even across a 40 sweep, then falls off quickly toward the edges. Fresnels end up used in flood position a lot. The flood/spot mechanism is often used for little more than to fine-tune the intensity. Note that in full flood, the beam has no central hot spot; the field is very even. As the lamp is spotted in, the rays become less divergent, more nearly parallel. The beam narrows and gets brighter in the center, falling off rapidly on either side. At full spot, the usable portion of the beam is narrow, about a 10 angle. The termthrow refers to the distance from the light to the subject. A lamp in spot position has a greater throw; it illuminates the subject to the same brightness at a much greater distance. Table A.3 (Appendix A) gives the intensity at any distance for a variety of fixtures.
Photometrics, beam angle, and field angle are terms used in light manufacturers’ sales literature; it is sometimes useful data to have during planning, but these are not terms you are likely to hear on set. In practice, electricians use these concepts all the time. For example, say that a large room is to FIGURE 3.4
(A) A plano-convex lens pulls together the divergent rays of light. (B) A Fresnel lens has the same optical effect as the plano-convex lens, but it is cut away to reduce weight and heat retention.
2Photometric data provided by a lighting manufacturer indicates the intensity of the light throughout its range of spot and
flood. A typical Fresnel has a range from about 10to 45or 50. Table A.2 gives the beam diameter at various distances for given beam angle.
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Fresnels
Axially mounted single-ended lamp Parabolic Aluminized Reflector Parallel rays (from the reflector) Double-ended
quartz envelope (filament along focal point of parabola) Parabolic Aluminized Mirror Reflector PAR Lamp Fresnel Fixture Fresnel Fixture Fresnel Lens Spherical Reflector Lamp Center Flood Position A C D Spot Position
Fresnel Fixture Open Face Fixture
Concentrated Rays Reflector in spot position Direct rays Reflector in flood position Divergent Rays Direct rays Axially Mounted Lamp Elipsoidal Reflector Focusing Plane Shutters Gobo Slot Condenser Lens
Elipsoidal Reflector Spotlight
Axially-mounted lamp in parabolic reflector Spreader Lens
Spreader Lens
B
E
FIGURE 3.5
The design of the optical train—lamp, reflector, and lenses—affects the degree of control one has over the resulting beam as well as its efficiency and quality of the light. (A) Fresnel lights use a spherical reflector coupled with the Fresnel lens. (B) An open-face fixture comprises a simple lamp and reflector (which in this case has adjustable focus). (C) A parabolic reflector is used in PAR lamps and beam projectors to create a near-parallel shaft of light. (D) Many modern par fixtures employ an axially mounted lamp in a par reflector. (E) The ellipsoidal reflector on a spotlight requires focuses all the light gathered by the reflector. This allows the light to shape the beam with framing shutters and gobo patterns and project it onto a surface in sharp focus or de-focused.
Beam Area 50% 10% Field Area Hot Spot 100% FIGURE 3.6
The field defines the “usable” light—the area of light that has an intensity of at least 10% of the peak value. Beam is defined as the “working light”, the area of light that has an intensity of at least 50% of the peak value. The hot spot is the brightest spot within the beam. The terms beam angle and field angle refer to the angle, from the fixture, of the beam and field, respectively.
50,000 45,000 40,000 35,000 30,000 25,000 Candela 20,000 15,000 10,000 5,000 30 20 30
Left hand Right hand
Full flood Full spot Spot = 48,000 cd Beam angle (50%) = 10 Beam angle (50%) = 49 Field angle (10%) = 21 Field angle (10%) = 63 Flood = 7,500 cd Divergence () 20 10 0 10 FIGURE 3.7
A polar distribution graph depicts light intensity across the diameter of the field of light. The upper tick marks denote the beam angle (the “working” light); the lower tick marks denote the field angle (the “usable” light). In the flood position, the light offers virtually even intensity across the wide spread of the beam; in the spot position, beam intensity falls off rapidly outward from the central hot spot.
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Fresnels
be lit using several lights spaced evenly along one wall of the room. To make the light intensity even across the whole room, the lamps are set at full flood, and the edge of the beam of each light is feath- ered into that of the next. The beams overlap slightly at the 50% point, creating an even 100% inten- sity across the entire space. It is fairly easy to calculate the intensity and beam diameter of any light that has a focused beam (doing so for softlights is not so straightforward). Acandela (cd) is a unit of luminous intensity (or candle power) equal to: cd¼ foot candles (distance in feet)2. Making photometric calculations is covered in detail in Appendix A.
A Fresnel creates its hardest, most delineated shadows at full flood. The more spotted-in the fixture, theless sharp the shadow lines appear. In full spot position, rays from the Fresnel travel more nearly parallel, but some converge slightly and cross one another. This creates a fuzziness to any shadow cast from an object. If one wants to project a sharp shadow or make a silhouette (e.g., the classic gag of a silhouette cast on a closed curtain), one would want to use a light at full flood.
Fresnel accessories
Fresnel lights should always be accompanied by barn doors and a set of scrims in a scrim box or scrim bag. A typical equipment package also includes snoots for each size of Fresnel light.
Scrims
A scrim is a stainless-steel wire screen used to reduce the intensity of the light. A single scrim has a loose wire weave, is identified by its green ring frame, and cuts the intensity of the light by approxi- mately a half stop. A double scrim has a tighter weave, is identified by its red ring frame, and cuts the light by approximately one full stop. A standard Hollywood set of scrims includes a single, two doubles, a half-single, a half-double, and a gel frame. Quarter scrims and graduated scrims are also available for some fixtures.
Half scrims affect just one half of the beam. A “bottom-half double” can be used to even out the intensity of the light as the subject moves closer to the fixture (Figure 3.8). It reduces the light falling on objects close to the light, bringing the light level down to that of objects farther from the light.
FIGURE 3.8
A bottom-half scrim is used to even out intensity as the subject moves closer to the light fixture.
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CHAPTER 3 Light fixtures: The basic tungsten arsenal
A gel frame can be used to hold gels or diffusion for short spans of time; however, because of the heat close to the lens, many lights melt gels mounted in the gel frame. Similarly, hot scrims melt the gel in a gel frame (and make a big gooey mess on the scrim). Therefore, gels and diffusion materials are often attached to the barn doors, spaced apart from the hot scrims.
Barn doors
Barn doors provide the most basic control over the placement of the edges of the beam. Because the doors are so close to the fixture, the cut is fairly soft (Figure 3.9). Barn doors typically have two large leaves and two smaller triangular ones. When the bigger doors are horizontal, they are said to be “Chinese”; when vertical, “American.” By closing the two large leaves into a narrow slit and folding the small leaves out of the way, you can make a narrow slash. The slash can be hori- zontal—for an eye light, for example—or turned diagonally to make a slash across a background.
Snoot
When a very confined, narrow, circular beam is desired, replace the barn doors with a snoot. Snoots come in various sizes, from wide (called atop hat) to very narrow (stovepipe). Some snoots are fitted with four rings with different aperture sizes so that you can adjust the beam width (Figure 3.10). You might use snoots, for example, if you wanted to light a set with small pools of light—lighting tables in a cafe´.
Focal spot
The focal spot attachment is a hold over from a time when Fresnel lights were pervasive in motion picture sets and ellipsoidal spotlights were not typically part of the lighting package. A focal spot essentially changes a Fresnel into a spotlight. The focal spot lens assembly creates a narrow, bright, even circle. Like an ellipsoidal reflector spotlight, a focal spot has framing shutters. It accepts design patterns called gobos and mattes, which can be projected and focused onto the scene. It has FIGURE 3.9
Barn doors contain the light, putting a straight edge on the beam.
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Fresnels
interchangeable lens tubes—wide-beam and narrow-beam. It also comes with a gel ring to add color gels. A focal spot attachment is actually a very poor substitute for an actual ellipsoidal spotlight such as the Source Four discussed later in this chapter.
Shutters
Shutters are like heavy-duty louvers or blinds (Figure 3.11); they have rows of parallel slats that open and close. The shutter is mounted on the front of the light. The shutter can be controlled to smoothly reduce the amount of light getting to the subject. Shutters are handy when the light level needs to change during a shot. Care must be taken to avoid projecting a Venetian-blind pattern on the subject. Keep the light some distance from the subject and use diffusion material. Be watchful also for a vertical shift in the position of the beam as the shutters are closed. Shutters can be used to create a lightning effect; opening and quickly closing the shutter can produce a sudden flash. Use appropriate caution; the shutters will warp from the heat buildup if kept closed for too long.
20k and 24k tungsten Fresnels
For almost a century, the biggest single-source tungsten light was the 10k. The advent of 20k and 24k lamps (in 1998) paved the way for a variety of 20k and 24k fixtures, including Fresnel fixtures, skypans, and beam projectors. The 20k Fresnel lights typically have a large 30-in. Fresnel lens and are great for creating sunlight steaming in through windows when working on a sound stage, or for lighting a large area for a night exterior.
20k lamps are typically powered through a stand-alone dimmer. A dimmer is used to bring the lamp up to intensity more slowly than a switch does. These large lamps have a very high inrush current when started cold. The inrush current is hard on the lamp, and the lamps are expensive. FIGURE 3.10
(A) A snoot with multiple aperture rings allows some flexibility in beam width. (B) A snoot confines the beam to a narrow circle.
Lamps are now available in various voltages: 208, 220, 230, and 240 V. It is important to match the lamp installed to the voltage of the system you are using. A 208-V bulb will be stressed if 240 V is applied to it. Conversely, a 240-V bulb running on 208 V will not have as much output and will have a warm color temperature.
The lamp and its installation
Lamps are referred to by a three-letter code assigned by the American National Standards Institute (ANSI). For example, a typical 1k Fresnel uses an EGT bulb. ANSI codes are listed in Appendix B. Most larger Fresnels used in motion picture work have a bipostal (two-pin) lamp base. Smaller lamps, such as the 200 W FEV, have a bayonet base. Bulbs are listed by base type in Table B.3. Figure 3.12 shows how to open up various models of lights to get at the globe.
On small units, the bulb simply plugs straight into the lamp base and is held in place by friction. When removing the bulb from this type of base, be careful not to break the glass off its porcelain base. Firmly grasp the porcelain base and wiggle the globe out. Do not handle the glass. On lights 2000 W and larger, a screw in the fixture’s lamp base tightens the base around the pins of the bulb. The globe comes out freely when the thumbscrew is loosened.
The position of the lamp relative to the reflector is critical to the proper operation of the light. The filament of the bulb sits precisely at the focal point of the reflector. Therefore, if the bulb is not seated properly or the reflector is bent, the lamp’s performance is drastically reduced.
FIGURE 3.11
Shutters can be manually activated or motorized as shown here. These DMX512-controlled shutters are activated from a dimmer board or DMX512 remote slider.
(Courtesy Mole-Richardson Company, Los Angeles, CA.)
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Fresnels
Tilt angle
To ensure proper heat dissipation, manufacturers recommend that Fresnels be hung with the base down. Each type of globe has a limit to the amount it can be tilted on its side without shortening the life of the globe. For example, a senior (a 5k Fresnel fixture) should burn with the bulb oriented within 45 of vertical. In addition to damaging the bulb, a 2000-W baby junior light hung at an extreme downward tilt will melt the reflector. In practice, the tilt angle is a concern only with lights that have large, expensive globes. Small lights are hung in whatever manner is required.
SOFT LIGHTS
Soft lights (Figures 3.13 and 3.14) are designed to produce diffused light with less-defined shadows. Light from the long tubular globes is directed into a white concave reflector. Because it is indirect, bounced off a diffuse white surface, and exits through a relatively large aperture, the resulting light is soft and has a wide, even, uncontrolled spread. Soft lights are commonly used for fill and general room ambiance.
Because soft lights use indirect light, they produce far less light per watt than Fresnels. Most soft lights have multiple globes, each switched individually, making it easy to increase or reduce the light’s intensity. Figure 3.15 shows the egg crate and snoot, which can also be used to contain and control soft light. A gel frame is also a standard accessory. Soft lights do not generally have scrims, but you can improvise by inserting a baby scrim between the base and the white reflector surface, sandwiched with the egg crate and held in place with a grip clip.
To maintain maximum intensity and proper color temperature, the white reflector must periodi- cally be cleaned or repainted. When repainting the interior surface, use “best boy white” paint. Best boy white reflects light without changing the color of the light and withstands high temperatures. If regular white paint is used, it will appear off-color.
FIGURE 3.12
Four common ways to access the inside of a Fresnel fixture. (A) With most lights 1000 W and larger, the lens door swings open on a hinge. (B) On a baby-baby, the top of the housing swings back on a hinge at the back of the fixture. (C) The top of a Pepper’s housing swings open to one side. (D) The lens of a midget is held in place by a metal tab. Push down the tab to take out the lens.
FIGURE 3.13
Anatomy of a 2k zip soft light.
FIGURE 3.14
Soft lights and their accessories. (A) Egg crate: this black, metal grid helps control spill. It is a good idea to keep an egg crate with each soft light because they are used frequently. (B) Diffuser frame (shown here placed on the front of a snoot): this square gel frame fits in the front of the unit to hold colored gel or diffusion. (C) 750 W zip. (D) 4k soft. (E) 8k Softlite with eight 1k globes.
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Soft lights
To gain access to the lamps, loosen the finger screws that lock the basket to the reflector and hinge the base open. The lamps are double-ended and held in place in a spring-loaded porcelain base. To install the lamp, insert one end and push back the spring until the other end can slide in.
“BAG” LIGHTS
Soft light is often created by shining a light through a frame of diffusion held by a C-stand; how- ever, a bag light greatly reduces time and clutter on set because it essentially replaces diffusion frames and flags with a single lightweight, self-contained accessory that attaches directly to the front of a light. A fabric softbox or bag light (commonly known as a Chimera, which is the name of one manufacturer) is an accessory designed to create pleasing soft light by diffusing the light rays and