magasa的小站Lighting for Technicolor Motion Pictures
by C. W. HANDLEY
1935
The introduction of the Technicolor three-color process of color photography into the motion picture studios brought forth the need for improved studio lighting equipment. All known color processes involve filtering or breaking up the light entering the camera into the primary colors, and recording each color upon a separate emulsion. Obviously, in a three-color process, a lower intensity of illumination falls upon each of the three negatives than upon the single negative used in black-and-white photography, because the latter receives all the rays passing through the camera lens. It is therefore necessary that the stage illumination be of higher intensity than required for black-and-white photography in order to attain corresponding photographic speed. Furthermore, since the color-sensitivity of the three negatives and the color-balance of the process as a whole is designed to render accurate color tones under daylight illumination, it is highly desirable that the light-source used in the studio should have a spectral energy distribution conforming closely to that of natural sunlight.
It is true that the same photographic effect can be attained with a light-source differing in quality from that of sunlight by using suitable filters. This, however, involves the absorption of a portion of the light reflected from the set, and a consequent reduction of photographic speed. The fact must always be recognized that filters never add light of any color. They merely reduce the intensity of the colors they are designed to suppress. Any increase of temperature on the set over that experienced in black-and-white productions is highly undesirable. It is accordingly evident that changes in lighting equipment must be of a character to provide an increase of photographic light of daylight quality without exceeding the amount of radiant heat projected upon the stage by the lighting equipment used for black-and-white photography.
THE BROADSIDE
The white-flame carbon arc has long been recognized as a light-source of high photographic efficiency and as one providing photographic effects essentially equivalent to those of sunlight. The old type of broadside lamp, burning 1/2 by 12-inch whiteflame carbons at 40 or 45 amperes were extensively used in the days of silent pictures. The mechanism of these lamps is of such design, however, that it is practically impossible to adjust it so that it will operate with the quietness necessary when used in proximity to sound recording equipment. Furthermore, higher intensities of illumination than these units are capable of supplying are required to meet the needs of the Technicolor process satisfactorily with a reasonable number of lamps upon the set. Since the broadside, used for floor lighting, and the scoop, for overhead lighting, provide the broad level of general illumination for the set as a whole, they constitute the most important elements of the lighting equipment. It is these units that establish the general color-tone of the scene in Technicolor photography.
The research laboratory of the National Carbon Company undertook the development of a new carbon to fulfill the specific needs of this new photographic process. The result of the research was a metal-coated carbon 8 millimeters in diameter, designed for operation at 40 amperes. Its characteristics have been described in detail by Joy, Bowditch, and Downes.(1) Due, in part, to the high currentdensity at which these carbons are operated, their light departs somewhat from the normal characteristics of the white-flame carbon arc and takes on more of the character of the high-intensity arc. In fact, through the photographically effective range, the relative intensity of radiation at various wavelengths is almost indentical to that of the 13.6-mm. high-intensity projector carbon arc operated at 125 amperes.
The development of a suitable lamp for use with these carbons was then accomplished through cooperation with an established lamp manufacturer. Two lamps were designed and made available to the motion picture studio : the twin-arc broadside lamp, MR-29, shown in Fig. 1, and the twin-arc scoop, MR-27, shown in Fig. 2. A detailed discussion of the development of these lamps has been given by Mole(2) together with a statement of the specifications that had to be fulfilled in adapting them to color photography. These units burning the new National motion picture studio carbons deliver somewhat more than the required 200 foot-candles at 15 feet; give an even distribution of light, constant in quality and intensity; provide a spectral energy distribution very similar to that of sunlight; and fully fulfill the requirements of silence imposed by the sound technicians. They have proved highly efficient for black-and-white photography, and practically a necessity for color photography. A comparison of the spectral energy distribution of the light from these lamps with that of natural sunlight is given in Fig. 3. A distinct advantage of this light, as pointed out by Joy, Bowditch, and Downes,(1) is that more than 40 per cent of the radiant energy emitted is photographically effective.
SUPPLEMENTARY LIGHTING UNITS
While broadsides and scoops provide the general level of set illumination and are highly satisfactory for the front and side lighting, their use without supplementary equipment would result in flat and uninteresting photographic effects. Accordingly, very powerful lighting units are placed in elevated and other strategic positions when strong shafts of light are required to pierce the even intensity of illumination supplied by the broadsides and the scoops. These larger units are used also for increasing the intensity of light in any given area, thereby separating points of special interest from the remainder of the set. The units used for this supplementary lighting are the spotlights and sun arcs, powerful carbon arc lamps that utilize the high-intensity principle first applied to searchlights and later extensively adopted for motion picture projection.
THE 80-AMPERE ROTARY ARC SPOTLIGHT
The 80-ampere rotary arc spotlight is used for back-lighting and to increase the intensity of illumination at any point where projected light is required, where the increase desired does not demand the power of a sun arc. It is in regular use in most of the studios and has been adapted to sound by the use of fiber gears which reduce mechanical noise. Some of them are fitted with snap-switches to cut out the control motor when the unit is close to the microphone. They are operated at 75-80 amperes with 50-55 volts at the arc. The operating element of an 80-ampere rotary spotlight is shown in Fig. 4.
To insure full efficiency and uniform photographic effect, reasonable attention should be given to the maintenance of these lamps and to preserving correct conditions of operation. A recent examination of several of them in operation revealed considerable variation in the quality and quantity of light emitted. This resulted from various causes, all easily removed or prevented. A badly pitted and soiled condenser was found to cut out as much as 40 per cent of the total light output. A variation of l/2 inch in the arc-gap (not uncommon in practice) changed the spectral energy distribution sufficiently to be noticeable in the Technicolor negative. In order to arrive at a standard for this type of unit in one instance, a lamp was fitted with a clean condenser free from pit marks, the best arc length (approximately 1/2 inch) was maintained, a spot three feet in diameter was focused upon a white wall thirty feet from the unit, and the direct light was measured with a standard Weston photometer fitted with a filter that reduced the intensity to within the limits of the instrument. The figures so obtained are used in checking other units of this type.
The spectral energy distribution of the 80-ampere rotary spotlight is higher at the blue end of the spectrum than that of the broadside lamp. A satisfactory color balance is maintained by the use of straw-colored gelatin in front of the condenser. Although this filter is very light, it reduces by more than 20 per cent the photographically effective radiation of the lamp. The need for the development of a new lamp, to give the desired spectral energy distribution without the use of a filter, is therefore indicated. In all probability such a lamp should have a different carbon trim from that now being used in rotary spotlights.
THE SUNLIGHT ARC
Two sizes of Sunlight arc are in common use, the mirror diameters of which are, respectively, 24 inches and 36 inches. They are designated as 24-inch Sun arcs and 36-inch Sun arcs. A 36-inch Sun arc is shown in Fig. 5. These lamps are used where the highest intensity of projected light is required, as in back-lighting when the action calls for a high level of foreground illumination; where well-defined shadows are desired; where a clearly defined streak of light cuts through the general illumination; and for producing high intensities of general illumination of great penetration. In the latter case diverging doors composed of strips of cylindrical lenses are often used in front of the lamp houses.
The spectral energy distribution of the light from this lamp is similar to that from the rotary spotlight, and, likewise, requires the use of a light straw filter to establish accurate color balance. There is accordingly evident need for further development of this type of unit to eliminate the necessity of using a filter.
THE 36-INCH SUN SPOT
The 36-inch Sun spot is similar in appearance and design to the 36- inch Sun arc except that it uses as a light-source a 10-kw. special tungsten lamp. It is used where a color contrast is desired and where warmer tones predominate; as behind windows, where the effect of the increased red radiation creates the illusion of the yellow-orange of afternoon sunlight.
JUNIOR SOLAR SPOT
The Junior Solar spot is a newly developed unit fitted with a special prismatic front lens and a spherical mirror. It is equipped with a 2000-watt, G-48 tungsten lamp which may be moved to a flood position or to a focus where it delivers a highly concentrated beam.
DIFFUSING MEDIUMS AND LAMP COLOR FILTERS
As previously stated, some of the high-intensity Sun arcs and 80- ampere, rotary-arc spotlights are fitted with straw-colored gelatin filters to cut out an excessive amount of blue. In addition to these, gelatin hangers of various colors are available so that the spectral energy distribution of any lamp may be changed at will to suit the requirements of the scene. Frosted gelatin hangers are used to soften the light from certain lamps. The Sun arcs have, as auxiliary equipment, diverging doors for use in spreading the beam on its horizontal transverse axis. The broadsides are fitted with " Factorlite" glass screens. These are sand-blasted on one side and molded on the other, making excellent diffusing mediums.
ARC-SILENCING DEVICES AND METHODS
Methods of silencing arc lights have been perfected by the studios. In 1930, W. Quinlan, Chief Engineer of the Fox Studios, produced and equipped that studio with complete sound filtering devices. These units consist of high-capacity electrolytic condensers connected across the bus-bars of the generator, and individual choke-coils mounted as an integral part of each lamp.(3) Other studios use highcapacity condensers of the dry type, and individual choke-coils for the various types of units. L. Kolb, Chief Electrical Engineer of M-G-M Studios, has developed larger choke-coils rated at 1000 amperes, which are mounted upon rollers and may be used at the power house. These developments, together with the previously mentioned development of the new motion picture studio carbon arc, make possible the use of 100 per cent carbon arc illumination of the motion picture stage without the slightest interference with sound recording.
REFERENCES
(1) JOY, D. B., BOWDITCH, F. T., AND DOWNES, A. C.: "A New White-Flame Carbon for Photographic Light," /. Soc. Mot. Pict. Eng., XXII (Jan., 1934), No. 1, p. 58.
(2) MOLE, P.: "A New Development in Carbon Arc Lighting," J. Soc. Mot. Pict. Eng. t XXII (Jan., 1934), No. 1, p. 51.
(3) Report No. 2, Producers and Technicians Committee, Acad. Mot. Pict. Arts & Sciences (May 7, 1930).
1935
The introduction of the Technicolor three-color process of color photography into the motion picture studios brought forth the need for improved studio lighting equipment. All known color processes involve filtering or breaking up the light entering the camera into the primary colors, and recording each color upon a separate emulsion. Obviously, in a three-color process, a lower intensity of illumination falls upon each of the three negatives than upon the single negative used in black-and-white photography, because the latter receives all the rays passing through the camera lens. It is therefore necessary that the stage illumination be of higher intensity than required for black-and-white photography in order to attain corresponding photographic speed. Furthermore, since the color-sensitivity of the three negatives and the color-balance of the process as a whole is designed to render accurate color tones under daylight illumination, it is highly desirable that the light-source used in the studio should have a spectral energy distribution conforming closely to that of natural sunlight.
It is true that the same photographic effect can be attained with a light-source differing in quality from that of sunlight by using suitable filters. This, however, involves the absorption of a portion of the light reflected from the set, and a consequent reduction of photographic speed. The fact must always be recognized that filters never add light of any color. They merely reduce the intensity of the colors they are designed to suppress. Any increase of temperature on the set over that experienced in black-and-white productions is highly undesirable. It is accordingly evident that changes in lighting equipment must be of a character to provide an increase of photographic light of daylight quality without exceeding the amount of radiant heat projected upon the stage by the lighting equipment used for black-and-white photography.
THE BROADSIDE
The white-flame carbon arc has long been recognized as a light-source of high photographic efficiency and as one providing photographic effects essentially equivalent to those of sunlight. The old type of broadside lamp, burning 1/2 by 12-inch whiteflame carbons at 40 or 45 amperes were extensively used in the days of silent pictures. The mechanism of these lamps is of such design, however, that it is practically impossible to adjust it so that it will operate with the quietness necessary when used in proximity to sound recording equipment. Furthermore, higher intensities of illumination than these units are capable of supplying are required to meet the needs of the Technicolor process satisfactorily with a reasonable number of lamps upon the set. Since the broadside, used for floor lighting, and the scoop, for overhead lighting, provide the broad level of general illumination for the set as a whole, they constitute the most important elements of the lighting equipment. It is these units that establish the general color-tone of the scene in Technicolor photography.
 |
The research laboratory of the National Carbon Company undertook the development of a new carbon to fulfill the specific needs of this new photographic process. The result of the research was a metal-coated carbon 8 millimeters in diameter, designed for operation at 40 amperes. Its characteristics have been described in detail by Joy, Bowditch, and Downes.(1) Due, in part, to the high currentdensity at which these carbons are operated, their light departs somewhat from the normal characteristics of the white-flame carbon arc and takes on more of the character of the high-intensity arc. In fact, through the photographically effective range, the relative intensity of radiation at various wavelengths is almost indentical to that of the 13.6-mm. high-intensity projector carbon arc operated at 125 amperes.
 |
The development of a suitable lamp for use with these carbons was then accomplished through cooperation with an established lamp manufacturer. Two lamps were designed and made available to the motion picture studio : the twin-arc broadside lamp, MR-29, shown in Fig. 1, and the twin-arc scoop, MR-27, shown in Fig. 2. A detailed discussion of the development of these lamps has been given by Mole(2) together with a statement of the specifications that had to be fulfilled in adapting them to color photography. These units burning the new National motion picture studio carbons deliver somewhat more than the required 200 foot-candles at 15 feet; give an even distribution of light, constant in quality and intensity; provide a spectral energy distribution very similar to that of sunlight; and fully fulfill the requirements of silence imposed by the sound technicians. They have proved highly efficient for black-and-white photography, and practically a necessity for color photography. A comparison of the spectral energy distribution of the light from these lamps with that of natural sunlight is given in Fig. 3. A distinct advantage of this light, as pointed out by Joy, Bowditch, and Downes,(1) is that more than 40 per cent of the radiant energy emitted is photographically effective.
 |
SUPPLEMENTARY LIGHTING UNITS
While broadsides and scoops provide the general level of set illumination and are highly satisfactory for the front and side lighting, their use without supplementary equipment would result in flat and uninteresting photographic effects. Accordingly, very powerful lighting units are placed in elevated and other strategic positions when strong shafts of light are required to pierce the even intensity of illumination supplied by the broadsides and the scoops. These larger units are used also for increasing the intensity of light in any given area, thereby separating points of special interest from the remainder of the set. The units used for this supplementary lighting are the spotlights and sun arcs, powerful carbon arc lamps that utilize the high-intensity principle first applied to searchlights and later extensively adopted for motion picture projection.
THE 80-AMPERE ROTARY ARC SPOTLIGHT
The 80-ampere rotary arc spotlight is used for back-lighting and to increase the intensity of illumination at any point where projected light is required, where the increase desired does not demand the power of a sun arc. It is in regular use in most of the studios and has been adapted to sound by the use of fiber gears which reduce mechanical noise. Some of them are fitted with snap-switches to cut out the control motor when the unit is close to the microphone. They are operated at 75-80 amperes with 50-55 volts at the arc. The operating element of an 80-ampere rotary spotlight is shown in Fig. 4.
 |
To insure full efficiency and uniform photographic effect, reasonable attention should be given to the maintenance of these lamps and to preserving correct conditions of operation. A recent examination of several of them in operation revealed considerable variation in the quality and quantity of light emitted. This resulted from various causes, all easily removed or prevented. A badly pitted and soiled condenser was found to cut out as much as 40 per cent of the total light output. A variation of l/2 inch in the arc-gap (not uncommon in practice) changed the spectral energy distribution sufficiently to be noticeable in the Technicolor negative. In order to arrive at a standard for this type of unit in one instance, a lamp was fitted with a clean condenser free from pit marks, the best arc length (approximately 1/2 inch) was maintained, a spot three feet in diameter was focused upon a white wall thirty feet from the unit, and the direct light was measured with a standard Weston photometer fitted with a filter that reduced the intensity to within the limits of the instrument. The figures so obtained are used in checking other units of this type.
The spectral energy distribution of the 80-ampere rotary spotlight is higher at the blue end of the spectrum than that of the broadside lamp. A satisfactory color balance is maintained by the use of straw-colored gelatin in front of the condenser. Although this filter is very light, it reduces by more than 20 per cent the photographically effective radiation of the lamp. The need for the development of a new lamp, to give the desired spectral energy distribution without the use of a filter, is therefore indicated. In all probability such a lamp should have a different carbon trim from that now being used in rotary spotlights.
THE SUNLIGHT ARC
Two sizes of Sunlight arc are in common use, the mirror diameters of which are, respectively, 24 inches and 36 inches. They are designated as 24-inch Sun arcs and 36-inch Sun arcs. A 36-inch Sun arc is shown in Fig. 5. These lamps are used where the highest intensity of projected light is required, as in back-lighting when the action calls for a high level of foreground illumination; where well-defined shadows are desired; where a clearly defined streak of light cuts through the general illumination; and for producing high intensities of general illumination of great penetration. In the latter case diverging doors composed of strips of cylindrical lenses are often used in front of the lamp houses.
 |
The spectral energy distribution of the light from this lamp is similar to that from the rotary spotlight, and, likewise, requires the use of a light straw filter to establish accurate color balance. There is accordingly evident need for further development of this type of unit to eliminate the necessity of using a filter.
THE 36-INCH SUN SPOT
The 36-inch Sun spot is similar in appearance and design to the 36- inch Sun arc except that it uses as a light-source a 10-kw. special tungsten lamp. It is used where a color contrast is desired and where warmer tones predominate; as behind windows, where the effect of the increased red radiation creates the illusion of the yellow-orange of afternoon sunlight.
JUNIOR SOLAR SPOT
The Junior Solar spot is a newly developed unit fitted with a special prismatic front lens and a spherical mirror. It is equipped with a 2000-watt, G-48 tungsten lamp which may be moved to a flood position or to a focus where it delivers a highly concentrated beam.
DIFFUSING MEDIUMS AND LAMP COLOR FILTERS
As previously stated, some of the high-intensity Sun arcs and 80- ampere, rotary-arc spotlights are fitted with straw-colored gelatin filters to cut out an excessive amount of blue. In addition to these, gelatin hangers of various colors are available so that the spectral energy distribution of any lamp may be changed at will to suit the requirements of the scene. Frosted gelatin hangers are used to soften the light from certain lamps. The Sun arcs have, as auxiliary equipment, diverging doors for use in spreading the beam on its horizontal transverse axis. The broadsides are fitted with " Factorlite" glass screens. These are sand-blasted on one side and molded on the other, making excellent diffusing mediums.
ARC-SILENCING DEVICES AND METHODS
Methods of silencing arc lights have been perfected by the studios. In 1930, W. Quinlan, Chief Engineer of the Fox Studios, produced and equipped that studio with complete sound filtering devices. These units consist of high-capacity electrolytic condensers connected across the bus-bars of the generator, and individual choke-coils mounted as an integral part of each lamp.(3) Other studios use highcapacity condensers of the dry type, and individual choke-coils for the various types of units. L. Kolb, Chief Electrical Engineer of M-G-M Studios, has developed larger choke-coils rated at 1000 amperes, which are mounted upon rollers and may be used at the power house. These developments, together with the previously mentioned development of the new motion picture studio carbon arc, make possible the use of 100 per cent carbon arc illumination of the motion picture stage without the slightest interference with sound recording.
REFERENCES
(1) JOY, D. B., BOWDITCH, F. T., AND DOWNES, A. C.: "A New White-Flame Carbon for Photographic Light," /. Soc. Mot. Pict. Eng., XXII (Jan., 1934), No. 1, p. 58.
(2) MOLE, P.: "A New Development in Carbon Arc Lighting," J. Soc. Mot. Pict. Eng. t XXII (Jan., 1934), No. 1, p. 51.
(3) Report No. 2, Producers and Technicians Committee, Acad. Mot. Pict. Arts & Sciences (May 7, 1930).
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