Proceedings of the British Kinematograph Society (1936)

at all permissible in colour photography with the processes now available for commercial use. Since the colour temperature of an incandescent lamp varies rapidly with a change in voltage, it is important to have adequate voltage control when incandescent lamps are generally used. Incandescent lamps have the advantage of being divisible into small or large units. We can have Baby Spots using 250 watt or 500 watt lamps, and from thereon up with a range of 1,000 watt, 2,000 watt. 3,000 watt, 5,000 watt and 10,000 watt units. No other light source is so easily operated as the incandescent lamp. The Are Lamp The Carbon Are which was very generally used for photographic purposes until the advent of panchromatic film stock, and talking pictures, lost considerable ground immediately after these two changes came into general practice. During the past ten years much has been written and said about the advantages of the Carbon Are as a source of photographic lighting. | However. it was not until considerable study had been given towards new design of auxiliary equipment that the Carbon Are was regarded with much favour for general photographic requirements. It has, of course, always been recognised that by reason of the crater of an Arc being almost a point source of light it had a distinct advantave over incandescent lamps in cases where beams of light with a very sharp ‘‘ cut-off ’’ were necessary. When it became apparent in colour photography that a light source was needed which much more nearly matched noon sunlight the impetus for greater research in the field of arc eauipment brought forth new equipment which is now being used very generally in black and white photography. In the manufacture of this equipment it was deemed necessary to design so that carbons can operate at the manufacturers’ rated amperage. The Vavour Discharge Lamps A third light source is being watched very carefully. I refer to the gaseous vapour discharge lamn. However, this source possesses both light and performance characteristics which render it unsuitable for motion picture studio lighting. Research is being carried on, and it is quite possible that this source may come into use if modifications can be made in its operating characteristics, SS Early Lighting Equipment Early lighting equipment consisted of a light source with a reflector at the back of it, which for the most part gave a flood of light on to the set. The best evidence of this type of lamp is still to be seen in the so-called twin broad-lamp, which in the incandescent field was an outgrowth of the twin side arc. Practice soon indicated the need of a light source which could be used as a modelling light, and the parabolic mirror spotlight and the plano-convex spotlight came into general use. The Disadvantages of the Parabolic Mirror Although the parabolic mirror spotlight is an extremely efficient unit when used as a spotlight, that is with a narrow beam divergence, it has the fault of throwing a beam pattern of ‘‘ hot’’ outside rings and dark centres as the beam is widened. Incandescent equipment has the further disadvantage of practically no control of the front light of the filament, which finally brought into use sets of louvres placed in front of the lamp, often called ‘‘ spill-rings.”’ a || pat Ram n =. pele HEIE | a iE: E TTT TT TT Pee F TTT TTT rep ae ERR RAeE: ; fl Bee it Ei —— ae ee — Raa Sakbsa 4s a = Pam ee ie et a oe (at RS ane a a — ca an a cated [ns waa mais fad SA EET S coh oH Fa Figure 1 Since it was then found difficult to keep these louvres exactly in position the total efficiency of the unit dropped con