TELEVISION PROJECTION SYSTEMS, PRESENT SITUATION AND FUTURE-PROSPECTS

The basic requirements of television projection systems according to their applications: picture size, brightness, contrast, resolution are recalled. Two main classes of projectors can be distinguished: the first is intended for consumer and semiprofessional applications and requires an output light flux ranging between 50 and 200 lm; the second is intended for professional applications and requires an output light flux ranging between 50 a 1000 and 5000 lm. The various kinds of projection displays are then classified according to the nature of: the light generator: phosphor screen, laser, projection bulb; the principle used for light modulation: power supply modulation, light diffraction or scattering, induced birefringence; the modulation medium: electron beam, solid, liquid crystal, liquid; the addressing means: electron beam, matrix, optical device with photoconductor. At present, all the projectors intended for consumer and semiprofessional market use cathode ray tubes with phosphor screens. For the professional market, the light flux and resolution requirements ask for image light valves. The main industrial and laboratory achievements are then described as well as future prospects.