ELLIPSOIDAL REFLECTOR SPOTLIGHTS The ellipsoidal reflector spotlight provides a controlled beam of light with typical instruments falling in the 500 to 2000 watt range. The normal beam pattern of these instruments is circular, but framing shutters commonly are provided to shape the beam. Also, this instrument can be used to project patterns of Iight. The most desirable condition is for the unmasked beam to be uniform, so all parts of the unmasked beam can be utilized and all mask settings are functional. Figure 5a shows the typical pattern produced by a standard ellipsoidal reflector spotlight. The dark areas at the top and bottom of the pattern are caused by the large hole required in the reflector to admit the lamp and by the lack of light emitted from the end of the lamp. Figure 5b shows a more desirable pattern for such instruments; this can be obtained by a new optical design. Figure 7 illustrates an adaptor for use In the ellipsoidal reflector spotlight to permit the use of 500 through 1000 watt tungsten-halogen lamps in existing fixtures. The performance with such substitutions is shown in Fig. 8. It is seen that improved performance can be obtained even with increased life. The necessity for proper alignment of the lamp in this type of instrument is evident. Panerns approximating those shown in Fig. 5b can result from misaligned lamps; the hot spot will not always be cen· tered in the pattern. The need to realign the fixture each Figure 7. Adapter to permit the use halogen lamps in existing equipment. a. of single-ended tungsten- b. Figure 6. Light patterns of ellipsoidal reflector spotlights. (a) Conventional unit showing dark areas caused by lamp orientation. (b) De· sign utilizing single-ended tungsten-halogen lamp to produce axiallysymmetric pattern. time a lamp is replaced becomes a major factor in the use of this instrument type. However, the problem is common to IJoth the tungsten-halogen lamp and the standard incandescent lamp. A fixture design to improve the performance of this instrument is shown in Fig. 9; the optical system is shown in Fig. 10. A small, compact coil, single-ended tungstenhalogen lamp is placed axially in the system. The elliptical reflector efficiently collects the light from the filament and images it at the aperture; here it is focussed by the lenses into the spotlight beam. Very uniform beams can be obtained from this form of system since the hole in the reflector to admit the lamp, and the lack of light from the end of the lamp are not optically involved in the system. A 50 per cent gain in lumen output can be obtained with this system. 22 THEATRE DESIGN AND TECHNOLOGY