US3733480A

US3733480A - Studio lighting apparatus

Info

Publication number: US3733480A
Application number: US00156436A
Authority: US
Inventors: W Glenn
Original assignee: Columbia Broadcasting System Inc
Current assignee: CBS Broadcasting Inc; Thomson CSF Broadcast Inc
Priority date: 1971-06-24
Filing date: 1971-06-24
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15
Also published as: DE2231139A1; IT958513B; GB1328610A; FR2143419A1; NL7208725A; FR2143419B1

Abstract

Apparatus for illuminating a background surface of a television studio or stage with white light comprising red, blue and green color components that are matched with the corresponding primary color sensitivity curves in a color television or film camera. The apparatus comprises an assembly of reflectors of elliptical shape supported in contiguous side-by-side relationship with successive reflectors positioned slightly higher than the last and having their major axes departing from the vertical to a greater extent than the last. Each reflector is illuminated by an elongated fluorescent lamp mounted at the focus of the reflector and having a primary color-emitting phosphor.

Description

lJnite States Patent [19] Glenn, Jr. 1 1 May 15, 1973 54] STUDIO LIGHTING APPARATUS 3,093,319 6/1963 Gamain ..240 1.1

[ Inventor: William E. Glenn Stamford 3,143,300 8/1964 Way ..240/3.l

Conn' Primary Examiner-Richard L. Moses [73] Assignee: Columbia Broadcasting System, Inc., Atmmey Granvie Brumbaugh Eben New York, Graves and Mark N. Donohue et al.

[22] Filed: June 24, 1971 App]. No.: 156,436

240/2 C, 3, 3.1,11.4 R, 11.4 N, 41.35 A, 41.35 D, 46.59, 51.11 R

References Cited UNITED STATES PATENTS 12/1930 Bertling ..240/41.35 A

[57] ABSTRACT Apparatus for illuminating a background surface of a television studio or stage with white light comprising red, blue and green color components that are matched with the corresponding primary color sensitivity curves in a color television or film camera. The apparatus comprises an assembly of reflectors of elliptical shape supported in contiguous side-by-side relationship with successive reflectors positioned slightly higher than the last and having their major axes departing from the vertical to a greater extent than the last. Each reflector is illuminated by an elongated fluorescent lamp mounted at the focus of the reflector and having a primary color-emitting phosphor.

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SHEET 9 [IF 9 COLOR TELEVISION CAMERA IINVENTOR. WILLIAM E. GLENN JR,

ZAZI W M his ATTORNEYS STUDIO LIGHTING APPARATUS BACKGROUND OF THE INVENTION This invention relates to lighting apparatus and, more particularly, to an assembly of reflector elements and fluorescent lamps for uniformly illuminating a vertical wall or backdrop of a television studio or stage.

It has long been the practice to illuminate television studios with incandescent lamps of the halogen-filled mercury vapor type in conjunction with corresponding colored filters to produce white light having appropriate proportions of red, blue and green to match the primaries of color television cameras. These lamps are of relatively high intensity, thus requiring substantial amounts of power for their operation and correspondingly large capacity air-conditioning equipment to remove the dissipated heat. Lamps of this kind cost between $l and each, have relative short lives and, because of their high wattage, require high wattage dimmers for controlling their intensity. Incandescent lamps also suffer from the disadvantage that when they are dimmed, the primary colors do not change equally but rather change by different amounts; i.e., the colors do not track with changes in intensity of the illumination.

Although a method of producing artificial illumination having the correct color brightness for monochrome photography and containing the correct colors for color photography is disclosed in US. Pat. No. 1,784,171, incandescent lamps continue to be used for stage and studio lighting in spite of their disadvantages. The lighting system described in this patent includes a number of light-producing devices operative to produce light of different colors (e.g., blue, green and red) the rays from which are mixed to produce an approximately continuous spectrum. The devices disclosed do not, however, include fluorescent lamps for producing primary colored light, nor does the patent suggest the concept of matching the primary colors of the light source to the primary color sensitivity curves of a color television or film camera.

SUMMARY OF THE INVENTION It is a primary object of the present invention to overcome the above shortcomings of illumination with incandescent lamps.

A more particular object of the present invention is to provide studio lighting apparatus which is less expensive to install and operate, provides a more uniform illumination, and gives a better match with the primaries of color cameras at all levels of illumination.

These and other objects are obtained by the combination of a plurality of elongated fluorescent lamps which contain different phosphors which produce light of the three primary colors, together with trimming filters for the respective lamps, which together produce white light, the primary colors of which are substantially matched to the primary color sensitivity curves of a color camera, be it a television camera or a film camera. The primary colors of the source, which when mixed together produce white light, are selected to match the three primaries of the color camera; that is, the red primary light produced by the source is substantially the same color as the red filter in a color television camera, for example, so that it doesnt excite either the green or the blue color camera. Similarly, the blue-emitting phosphor and its associated filter produce blue light of the same color as the blue filter in the camera so that it doesnt excite either the red or the green color cameras, and the green-emitting phosphor and its filter produces green light matched to the camera.

Substantially uniform illumination of a backdrop of extended height is obtained by mounting the fluorescent lamps in a fixture having a corresponding plurality of elongated reflectors, preferably of elliptical shape, supported in contiguous side-by-side relationship with successive reflectors positioned slightly above the last and having their major axes departing from the vertical to a greater extent than the last. Each reflector is illuminated by an associated elongated fluorescent lamp mounted at the focus of the reflector.

In a preferred embodiment of the invention intended for illumination of a background surface of a studio or stage, fluorescent lighting elements containing red, blue and green color-emitting phosphors are mounted in the reflectors. One lamp having red-emitting phosphor is mounted in the lowermost reflector, the lamp with the blue-emitting phosphor is mounted in the next reflector, a green-emitting phosphor lamp is mounted in the third reflector, and another red-emitting lamp is mounted in the uppermost reflector. Blue, green and red illumination of proper quality to match the characteristics of the color camera are obtained by using lamps with special phosphors in combination with highly transmissive and color selective blue, green and red filters mounted on the reflectors containing the corresponding color-emitting lamps. Being of essentially the same color, the filters do not appreciably reduce the light output.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a perspective view of an illustrative studio lighting fixture arranged according to the present invention;

FIG. 2 is a sectional view of the lighting fixture taken along line 2-2 of FIG. 1 and looking in the direction of the arrows;

FIG. 3 is a spectral energy distribution (S.E.D.) curve for a suitable green fluorescent lamp on which is superimposed the transmission characteristic of its associated filter;

FIG. 4 is an S.E.D. curve of the light output from the green fluorescent lamp-filter combination;

FIG. 5 is an S.E.D. curve for a suitable blue fluorescent lamp on which is superimposed the transmission characteristic of its associated filter;

FIG. 6 is an S.E.D. curve of the light output from the blue lamp-filter combination;

FIG. 7 is an S. E. D. curve for a suitable red fluorescent lamp on which is superimposed the transmission characteristic of its associated filter;

FIG. 8 is an S.E.D. curve of the light output from the red lamp-filter combination; and

FIG. 9 is a schematic view of a typical installation of the lighting fixtures of FIG. 1 in a color television studio.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the illustrative embodiment of a studio lighting fixture arranged according to the present invention, as shown in FIGS. 1 and 2, there is provided a fixture 10 which may be formed from wood, plastic, metal or the like. The fixture has a generally stepped configuration for receiving on its upper surface an assembly 12 of four elliptically shaped

reflectors

12a, 12b, 12c and 12d. The reflectors 12a-12d are supported by the fixture 10 in contiguous relationship with successive reflectors, i.e., 12b, 12c and 12d, positioned slightly higher than the last reflector, i.e., 12a, 12b and 12c, respectively. The longitudinal axes of the reflectors are parallel to each other and to the base of the fixture 10. Typically, the fixture has an overall length of 39 inches, a depth of 28 inches, and a height of seventeen inches.

As shown in FIG. 2, the reflectors 12a-12d lie along a generally curved line and have their major axes departing from the vertical by different amounts. Specifically, the major axis of the lowermost elliptical reflector 12a departs very slightly from the vertical plane, while the major axis of the next highest reflector 12b is offset from the vertical, in a direction toward the lower end of the fixture, to a slightly greater extent than the axis of reflector 12a. Similarly, the major axis of the next highest reflector 12c departs from the vertical to a slightly greater degree than does the axis of the reflector 12b, but to a lesser extent than does the axis of the highest reflector 12d. The inclination of the major axes of the reflectors are such that the conjugate focus of all four ellipses is at a point slightly above the center of the vertical surface to be illuminated. For a typical television studio lighting application, in which the backdrop is typically about twenty feet high, the major axes are so inclined to the vertical that when the center of the fixture is positioned about thirty-three inches from the vertical surface, the conjugate foci of the reflectors are at a point on the surface about eleven feet away from the fixture.

Each of the reflectors 12a-12d may be fabricated in a number of ways, the choice of fabrication being dictated by weight, cost, esthetic and other considerations. For example, the individual reflectors can be molded or vacuum formed from plastic or other suitable material, and the surfaces of the reflectors metallized or otherwise treated to give them the desired reflective properties. In a preferred embodiment, all four reflectors are vacuum formed from plastic as a single unit and the elliptical surfaces metalized to give the desired reflective properties.

An elongated fluorescent lamp having a primary color-emitting phosphor is mounted at the focus of each of the reflectors 12a-12d. In a preferred embodiment of the invention, a red light-emitting fluorescent tube 14a is mounted in reflector 12a at the focus thereof, a blue light-emitting fluorescent tube 14b is mounted in reflector 12b, a green-emitting fluorescent lamp 14c is mounted in reflector 12c and a second red-emitting lamp 14d is mounted in reflector 12d. The brightness of the light emitted by the selected red light-emitting fluorescent tube is approximately one-half the brightness of the light emitted by the blue and green lightemitting fluorescent tubes, this being the reason for using two red fluorescent tubes. It has been found that positioning the two red lamps in the lowermost and uppermost reflectors optimizes the color distribution over the entire illuminated area, but it may be satisfactory in some applications to position them otherwise; for example, the two red lamps may be positioned side-byside in the two uppermost reflectors, with the blue and green lamps positioned in the first and second reflectors, respectively.

The curved line along which the centers of the lamps l4a-l4d are disposed departs slightly from the arc of a circle, the curvature being so interrelated with the angles of inclination of the successive reflectors that the shadows of the lower edge of the four reflectors fall at essentially the same point on the vertical surface slightly below the front edge of the reflector assembly. This configuration causes the lamps to directly illuminate the lower portion of the backdrop (assuming that the fixture is placed on the floor) with light having a color corresponding to the color of the contiguous area illuminated by light reflected by the reflectors, and of an intensity which substantially matches the intensity of the illumination of the area illuminated by the reflectors. Accordingly, the illumination is substantially uniform in intensity and color over the entire height of the backdrop.

Fluorescent lamps having the red, green and blue light-emitting phosphors suitable for use in the present invention are made by GTE Sylvania and carry the designation T-8. These lamps are 1 inch in diameter and 3 feet long. The operating voltage across the lamp, with a proper ballast, is 98 volts and the current is 0.355 amperes. Such lamps are rated at 30 watts, but may be overdriven to watts to achieve the desired level of illumination while still giving an acceptable lamp life. The color temperature produced with all four lamps at equal power is about 3200 Kelvin which matches the color temperature of white incandescent lamps. The life of the fluorescent tubes is in the order of a thousand hours, vastly superior to the 25 hour lifetime of most incandescent lamps used for studio lighting.

The spectral energy distribution curves for the green, blue and red Sylvania T-8 fluorescent lamps are shown in FIGS. 3, 5 and 7, respectively. It will be noted that the distribution curves for the green and blue lamps are irregular, whereas the distribution curve for the red lamp is relatively smooth. The spikes in the phosphor curves are due to the mercury lines at about 4050 Angstroms (violet), 4348 Angstroms (blue), 5461 Angstroms (green) and 5770 Angstroms (yellow). To obtain the desired color purity of the light emitted by the lamps 14al4d and reflected by the reflectors 12a-12d, highly transmissive and color selective trimming filters 15a-15d are placed over the respective reflectors 12a-12d. Standard Cinemoid filters designated bright blue, moss green and orange and having the transmission characteristic shown in FIGS. 3, 5 and 7, respectively, are particularly suitable for this purpose. They may be bonded to rigid plastic and secured by suitable means, such as the S-shaped guides 18 shown in FIG. 2, in front of their corresponding fluorescent lamps. These filters being essentially the same colors as the colors produced by their respective lamps, the intensity of the light produced by the fixture is not appreciably reduced, but as will be seen from the S.E.D. curves of FIGS. 4, 6 and 8, the contaminating colors due to the mercury lines are substantially eliminated.

By using red, blue and green color-emitting fluorescent tubes to provide white light illumination of the background, there is provided automatically a matching between the primary color component light forming the white light and the red, blue and green filters in a color television camera. The discrimination between colors by the red, blue and green, camera tubes is comparable to the discrimination that would be achieved if signals corresponding to the primary colors were to be directly applied to the camera tubes.

Each of the lamps l4a-l4d is provided with an individual dimmer 16a, 16b, 16c and 16d (and associated ballast) which may be controlled either in unison or separately to achieve special color effects. Dimmers for fluorescent lamps are well known to the art and, accordingly, have not been shown or described in detail herein. Because of the low wattage of the fluorescent lamps, four dimmers are capable of handling an amount of light that would require more than 20 dimmers if incandescent lamps were used.

A significant advantage of using fluorescent lamps, rather than incandescent lamps for studio and/or stage illumination, is the gain in electrical power. In particular, available incandescent lamps for this purpose have relatively low luminous efficiency further reduced by the high filter factor required to produce the proper color. Since the luminous efficiency of fluorescent lamps is relatively high, the amount of power required to produce a given amount of light is lower by a factor of from to 15. This significant reduction in the dissipated heat allows a corresponding reduction in the capacity of the air-conditioning equipment normally required for the studio.

Furthermore, in using the primary color fluorescent lamps rather than incandescent lamps, the colors emitted by the lamps do not change when the lamps are dimmed. The colors track the primaries of the color camera regardless of the level of illumination. Also, with the above-described arrangement of reflectors 12a-12d, the colors are maintained uniformly the same over the entire illumination area. Still further, the overall height of the fixture 10, typically about seventeen inches, is sufficiently low so as not to be obtrusive in the studio.

As was noted earlier, the major axes of the four elliptical reflectors 12a-12d are so arranged that when the fixture 10 is placed near the base of a backdrop in a color television studio or stage to be lighted, the fixture gives a substantially flat white illumination of an area as wide as the length of the reflectors and extended in the vertical direction. A backdrop or wall of the usual height in television studios (about twenty feet) can be illuminated uniformly from top to bottom with one row of fixtures positioned near the base of the wall and one or two rows of fixtures suspended near the top and out from the wall. FIG. 9 shows an illustrative arrangement of the fixtures in a color television studio for illuminating a background surface 20; one row of fixtures 24 is positioned near the base of the surface 20, and one or two rows of fixtures 26a and 26b may also be positioned near the top of the surface 20. Presently available fluorescent tubes being 3 feet long, the number of fixtures required in each row will, of course, depend on the width of the background to be illuminated.

As was noted above, the focal lengths of the elliptical reflectors are chosen so that the fixtures provide the desired illumination when located about 30 inches from the background surface 20. Specifically, to illuminate a background surface having conventional dimensions, i.e., 20 feet high and 20 feet wide, and with the fixtures located approximately 30 inches out from the surface, the conjugate foci of the reflectors of the fixtures in rows 24 and 26 will be at points on the surface 20 about 11 feet from the fixture. With this arrangement, the background 20 is illuminated uniformly with a flat white illumination made up of primary color components that are matched perfectly with the color filters in the color camera 22.

Although the invention has been described herein with reference to a specific embodiment, many modifications and variations therein will now be apparent to those skilled in the art. For example, although the illuminating fixture has been described as having separate color selective primary color filters placed in front of corresponding primary color lamps, it is within the contemplation of the invention to use primary coloremitting lamps having appropriate primary color filter material coated on the outside of the lamp envelope. Fluorescent lamps of this construction are available, the filtering material being applied by dipping the lamp in a pigmented lacquer having the desired transmission characteristics. Also, the invention can be utilized to illuminate a background surface in any one or more of the primary colors or combinations thereof which produce a non-white illumination. In each instance, however, the color component light forming the background light will match the filters in a color television camera. And, although the invention has been described for use with color television cameras, its principles are equally applicable to the illumination of stages or sets for color film photography, in this case the primary colors of the light source being matched to the primary colors of the color film. Also, although reflectors of elliptical shape have been used in the preferred embodiment, it will be understood that the advantages of the invention may be realized with properly designed reflectors of parabolic, circular, or other shape, or combination thereof.

I claim:

1. Apparatus for artifically illuminating a studio or stage for viewing with a color camera having predetermined primary color sensitivity characteristics, comp g a bank of at least three fluorescent lamps a first of which contains a blue color-emitting phosphor, a second of which contains a green color-emitting phosphor, and at least one additional one of which contains a red color-emitting phosphor, the light intensity of the included red color-emitting lamps for the same input power being substantially equal to that of either the blue or green color-emitting lamps, said lamps being operative when simultaneously energized to emit light containing primary colors substantially matched with the primary color sensitivity characteristics of the camera, and

at least one highly transmissive and color selective primary color filter positioned to filter the light from one or more corresponding primary coloremitting fluorescent lamps for improving the match of the primary color light emitted by the lamps to the primary color sensitivity characteristics of the camera.

2. Apparatus in accordance with the claim 1 further including dimming means electrically connected with said lamps for independently varying the current flow through the lamps to thereby vary the intensity of light emitted in any given primary color so that the combined intensity of the bank of lamps can be varied without affecting the match of the emitted primary colors with the primary color sensitivity characteristics of the camera.

3. Apparatus in accordance with claim 1 further including an assembly of a like number of elongated reflectors of elliptical shape arranged side-by-side with a predetermined angular relationship between the axes of the reflectors, each of said lamps being mounted at the focus of a corresponding one of said reflectors, said angular relationship between the axes of the reflectors being such that the lamps directly illuminate an area in front of the reflectors and illuminate their respective reflectors to indirectly illuminate another area contiguous with the directly illuminated area.

4. Apparatus in accordance with claim 3 wherein successive ones of said reflectors are positioned higher than the last to such an extent, and have their major axes departing from the vertical in a direction toward the lowermost reflector to a greater extent than the last, such that the lamps directly illuminate an area in front of the reflectors and illuminate their respective reflectors to indirectly illuminate another area contiguous with the directly illuminated area.

5. Apparatus in accordance with claim 4 having four elliptical reflectors, and wherein the lowermost and uppermost reflectors have red color-emitting fluorescent lamps mounted therein, the next to the lowest reflector has a blue color-emitting fluorescent lamp mounted therein, and the other reflector has a green coloremitting fluorescent lamp mounted therein.

6. Apparatus for artifically illuminating a studio or stage for viewing with a color camera having predetermined primary color sensitivity characteristics, comp g a bank of at least four fluorescent lamps the first of which contains a blue color-emitting phosphor, a second of which contains a green color-emitting phosphor, and two of which contain a red coloremitting phosphor, the light intensity of the red color-emitting lamp for the same input power being approximately one-half that of the blue and green color-emitting lamps, said lamps being operative when simultaneously energized to emit light containing primary colors substantially matched with the primary color sensitivity characteristics of the camera, and corresponding number of highly transmissive and color selective primary color filters positioned to filter the light from the corresponding primary color-emitting fluorescent lamps for improving the match of the primary color light emitted by the lamps.

Claims

1. Apparatus for artifically illuminating a studio or stage for viewing with a color camera having predetermined primary color sensitivity characteristics, comprising, a bank of at least three fluorescent lamps a first of which contains a blue color-emitting phosphor, a second of which contains a green color-emitting phosphor, and at least one additional one of which contains a red color-emitting phosphor, the light intensity of the included red color-emitting lamps for the same input power being substantially equal to that of either the blue or green color-emitting lamps, said lamps being operative when simultaneously energized to emit light containing primary colors substantially matched with the primary color sensitivity characteristics of the camera, and at least one highly transmissive and color selective primary color filter positioned to filter the light from one or more corresponding primary color-emitting fluorescent lamps for improving the match of the primary color light emitted by the lamps to the primary color sensitivity characteristics of the camera.

5. Apparatus in accordance with claim 4 having four elliptical reflectors, and wherein the lowermost and uppermost reflectors have red color-emitting fluorescent lamps mounted therein, the next to the lowest reflector has a blue color-emitting fluorescent lamp mounted therein, and the other reflector has a green color-emitting fluorescent lamp mounted therein.

6. Apparatus for artifically illuminating a studio or stage for viewing with a color camera having predetermined primary color sensitivity characteristics, comprising, a bank of at least four fluorescent lamps the first of which contains a blue color-emitting phosphor, a second of which conTains a green color-emitting phosphor, and two of which contain a red color-emitting phosphor, the light intensity of the red color-emitting lamp for the same input power being approximately one-half that of the blue and green color-emitting lamps, said lamps being operative when simultaneously energized to emit light containing primary colors substantially matched with the primary color sensitivity characteristics of the camera, and a corresponding number of highly transmissive and color selective primary color filters positioned to filter the light from the corresponding primary color-emitting fluorescent lamps for improving the match of the primary color light emitted by the lamps.