PROJECTION TELEVISION DISPLAY DEVICE

Projection television display device comprising three monochrome projection television display tubes (20, 21, 22) each having a display screen (24, 25, 26) which is provided on the inside of the display window (23) and luminesces in a different colour, each tube having an optical axis extending perpendicularly from the centre of the display screen, the optical axes (33, 34, 35) of the three display screens being co-planar and the axes (34, 33) of the display screens of the first and second tubes (20, 22) conciding and the axis (35) of the display window of the third tube (21) constituting the main axis of the device, said axis being perpendicular to the two coincident axes (33, 34), said device further comprising two flat dichroic intersecting reflective mirrors (27, 29) extending perpendicularly on said plane and through the point of intersection of the axes and each constituting an angle of 45° with the main axis, the first mirror (27) reflecting the image of the first display screen and the second mirror (29) reflecting the image of the second display screen into the direction of the main axis and away from the third display screen, interference filters being disposed between said display screens and mirrors for passing the desired colour of light. When in the said interference filters disposed between the luminescent material of the display screens and the display windows the reflection greatly increases for light rays constituting an angle of more than 20 to 35° with the mormal on the filter and when there is substantially no transmission up to 90°, there is a gain in brightness by a factor of 1.5 to 2, a gain in contrast by more than a factor of 2 and also a considerable colour improvement and reduction of colour errors when the conventional green and blue phosphors are used.