A bright-light portable phototherapy unit to modify biological rhythms has a housing in which there is a source for producing light energy having a major portion in the visible light range. The housing is to be placed adjacent to the body of a user for positioning and directing the light from the source through an opening in the housing to be applied to the eyes of the user. The light source can be one or more fluorescent lamps and the light incident on the eyes preferably is at least 2,000 lux and, more preferably, at least 8,000 lux.

A transmission type projection screen comprises a plurality of sheets. The front sheet nearest to the front observation side is an ambient light attenuating front sheet which is provided on its surface facing the rear side with first prism lenses formed by successively and horizontally arranging unit triangular prisms. Each unit triangular prism has a sharply inclined surface inclined at an angle of about 90.degree. to the surface of the front sheet, and a gently inclined surface inclined at an angle in the range of 5.degree. to 40.degree. to the surface of the front sheet. The first prism lenses are disposed with the gently inclined surfaces of the unit triangular prisms thereof facing upward. Second prism lenses may be provided on its surface facing the front observation side, each of the second prism lenses also having a sharply inclined surface and a gently inclined surface.

Provided is a rear projection screen apparatus having a rear projection screen, light rays from a projecter being incident upon the rear surface of the rear projection screen at steep angles, wherein a plurality of elongated prisms are formed on the rear surface of the screen, each prism having a reflection surface extending therealong, thereby the incedence light rays are internally reflected, and then transmitted through the medium of screen for emerging from the front surface of the screen on the viewing side, and the rear surface of the screen is in a curve shape which is convex toward the viewing side so that the brightness of the screen can be made to be uniform.

A light flux modulated by a picture is shot out from a liquid crystal projector, and projected on the rear surface of the transparent screen, and a user enjoys the picture from the front side thereof. The sawlike prismatic surface is formed on the rear surface of the transparent screen. Edges of the sawlike prismatic surface form concentric circles centering around a point which is given as an intersection of an optical axis of the projector and a downward extensions of the transparent screen. A face looking downward transmits the light flux incident thereon into the transparent screen efficiently on condition that an angle formed by the incident ray of light and the optical axis of the projector is greater than 40.degree. and less than 90.degree.. A face looking upward totally reflects the ray of light incident thereon to the light-shooting surface, if the aforementioned condition is satisfied.

An optical viewing device enabling visually handicapped persons to read ordinary textual material in full color, the device comprising a stage for holding the material and an X-Y positioner used to move the textual material on the stage; lights beneath the stage for illuminating the material; an objective to form a real image; a prism or mirrors for reflecting the imaging rays from the objective through 90 degrees and for reinverting the rays; two mirrors to reflect the rays to an approximately vertical, directional, controlled brightness rear projection screen, so that the imaging rays successively passing from the objective to the reflecting/reinverting prism or mirrors and the two mirrors form a real, erect enlarged image on the screen.