International projectionist (Jan 1959-Dec 1960)

More on New Projection Light Source: Philips' SPP Discharge Lamp First publication anywhere in the world of detailed data anent the Philips SPP radically new projection light source appeared in IP for November last (Vol. 33, No. 11, p. 8, et seq.). Additional specific information relating thereto is appended, culled from the report of the Progress Committee of the Society of Motion Picture and Television Engineers as published in its Journal for May, 1959 (Vol. 68, No. 5, p. 310). 'iiti|in>miirnr>f!iH!imiitH|trmmi|iitmii z I THE Philips gas-discharge lamp SPP consists of a quartz tube 3 1/4 inches in length and a maximum diameter of 1/4 inch, which makes an extremely small lamp. The discharge takes place inside a thin capillary tube with an arc length of about 2/3 inch. For film projection the lamp is driven by a pulsating direct current of 72 pulses per second or 3 pulses per frame. Light is produced only during these current impulses; in the intervals the lamp is dark. This lamp finally fulfills the old dream of cinema technicians: to be able to produce light only as long as it is necessary for actual projection, thus cutting the losses caused by the rotary shutter. SPP lamp can be loaded up to 800 watts. The average life of this inexpensive lamp is 33 working hours under full load. At lower loads, however, the working life is considerably extended. Spectral-Energy Distribution Unlike the incandescent lamp or the carbon arc, the luminous flux decreases no more than proportionally with the load, so that the luminous efficiency remains equally high. The extremely high current intensity during the impulse peaks at which values 10 times the mean value are reached, leads to a continuously uniform spectral-energy distribution, permitting excellent projection of color film. Both according to the way it is produced and to its spectral distribution, the SPP light can be classified as "cold", thus the film is hardly heated. Ultraviolet radiation is eliminated by an absorption filter contained in the lamp holder. The luminous flux of each individual lamp remains constant throughout its life, Only just before its ultimate breakdown the luminous flux shows a pronounced deterioration. The excellent properties of this gas-discharge lamp can only be fully utilized in a specially The Ph. lips SPP discharge lamp, shown here with holder, is only VA" wide, Vi" in diameter. film receives three flashes when stationary. Even for a high picture brightness the screen image shows no trace of flicker. The film is moved up while the lamp is completely dark. A projector equipped with this lamp accordingly does not require a rotary shutter and all light produced is completely utilized for projection. The SPP lamp operated at 800 watts produces the same luminous flux on the MAXIMUM SCREEN SIZE (FT.) FOR STANDARD LUMINOUS INTENSITY ASPECT RATIO: Matte-White 0.8 Average Angle of Vision 1.8 Narrow Angle of Vision 3.0 Standard 1:1.37 24 X 19 39.5 X 28.8 52.5 X 38 Wide Screen 1:1.85 26 X 14 39.5 X 21.3 52.5 X 28.3 CinemaScops 1 :2.34 34.5 X 14.7 52.5 X 22.3 62 X 28.5 designed, shutterless projector. A brief description of the working of the lamp and how it is utilized in the projector follows. Side-to-Center Distribution Since the lamp is small and may be placed without any risk in the immediate vicinity of the picture gate, its optical system can likewise be small. It consists of a cylindrical reflector not larger than 1/2 inch by 1/3 inch and two lenses, which form an image of the discharge in the objective lens. This explains the exceptionally high side-tocenter ratio of 95%. Every frame of the The Philips SPP discharge lamp is shown here in its housing, together with the turret carrying a spare lamp which by a simple turn provides for instantaneous replacement. \J-Jk screen as a high-intensity arclamp at a current of 60 amperes. The screen sizes attainable on a matte-white projection screen with a reflection factor of 0.8, on a screen with an average angle of vision with a reflection factor of 1.8, and on a narrow-angle screen with a reflection factor of 3.0 with the aid of a projection lens of F\\S>. are given in the accompanying table. Strongly reflecting screens, e.g., beaded screens, owing to their narrow angle of vision, are obviously unsuitable for large theatres. This should be kept in mind when consulting the table. Semi-Automatic Operation Particular attention should be drawn to the uniform illumination of the screen. Whereas for carbon-arc projection a sideto-center ratio of 75%, and for xenon projection an even lower ratio is considered permissable, the side-to-center ratio with SPP projection for both leftand right-hand edges is at least 95%. Operation of the SPP lamp is confined to switching on and off insofar as this is not automatically effected by the projector. When used, it does not produce any dust or noxious fumes, hence requires no ventilating device. It can readily be operated by any automatic de It is so small that it can be :together with a spare lamp and autoi ic changeover device in the projector. INTERNATIONAL PROJECTIONIST SEPTEMBER 1959 15