The use of metal-halide discharge lamps for film lighting (Part 2)

Abstract

Intensity variations of light from a discharge lamp, occurring at twice the alternating supply frequency, can lead to a cyclic variation in frame-to-frame exposure if such lamps are used as light sources in motion picture film work. The visibility of picture luminance fluctuations brought about by such exposure variations is discussed, and limits of film exposure variation are recommended. Practical magnitudes of exposure variation are examined. Using these factors, relationships are derived between camera frame frequency and shutter angle, and lamp supply frequency and intensity variation magnitude, such that practical picture luminance variations are not perceptible. An assessment of a 'safe' lamp supply frequency is described, above which the appearance of picture luminance fluctuations may be discounted. The effect of ripple asymmetry (differing magnitudes of successive intensity maxima) is discussed. Experimental techniques for measuring intensity variations under standardized conditions are described, and the characteristics of two currently-available metal-halide discharge lamps are examined.

Get full access to this article

View all access options for this article.

References

Taylor, E.W. On the visibility of luminance fluctuations in television pictures, and exposure variations in motion picture film. BBC Research Department Report No. 1975/13.

CCIR XIII Plenary Assembly, Geneva XI, 65 (Recommendation 500, Table III) (1974).

Fisher, R.A. Statistical methods for research workers. Oliver and Boyd , Edinburgh, 1946. 3a. Ibid. p. 44. 3b. Ibid. p. 114.

Dow, J.S. The speed of flicker photometers. The Electrician, 59, 255 (1907).

De Lange DZN, H. Research into the dynamic nature of the human fovea → cortex systems with intermittent and modulated light. 1. Attenuation characteristics with white and colored light. J. Opt. Soc. Amer. , 48, 777 (1958)

Taylor, E.W. Television co-channel interference at very low offsets. BBC Research Department Report No. T-088, Serial No. 1962/19.

Barrett, H.A. , Barlow, R.E. , Lovick, R.C. and Norris, J.C. Improved telecine image quality: the influence of black level. Journal SMPTE, 82, 829 (1973).

Taylor, E.W. Some aspects of the use of metal-halide discharge lamps for film lighting . BBC Research Department Report No. 1976/2.

Mees, C.E.K. The theory of the photographic process. (New York, Macmillan, 1948).

10.

Taylor, E.W. Film lighting using metal-halide lamps: some operating conditions giving freedom from picture luminance fluctuations. BBC Research Report No. 1977/19.

11.

Taylor, E.W. Metal-halide discharge lamps: the measurement of intensity ripple and a note on operation at high supply frequencies. BBC Research Department Report No. 1977/23.

12.

Taylor, E.W. Film lighting using metal-halide lamps: the effect of intensity ripple asymmetry . BBC Research Department Report No. 1977/8.

13.

Taylor, E.W. The HMI 575-watt metal-halide discharge lamp: measurements and predicted effects of intensity ripple using sinusoidal lamp excitation. BBC Research Department Report No.1977/29.

14.

Dobrusskin, A. Metal-halide lamps with rare earth additives . Lighting Research and Technology, 3, 2, 125 (1971).

15.

Kugler, I. Progress in production of artificial daylight for film and television. BKSTS Journal, 58, 194 and 206 (1976).

16.

Taylor, E.W. The CSI 1kW metal-halide discharge lamp: measurements and predicted effects of intensity ripple using sinusoidal lamp excitation. BBC Research Department Report No. 1977/46.

17.

Aldworth, R.C. The development and application of metal-halide lamps for color filming and television. J. Soc. Motion Pict. Telev. Engrs., 84,70 (1975).

18.

Aldworth, R.C. The application of CSI lamps. BKSTS Journ., 58, 198 (1976).