LIGHT GUIDES AND BACKLIGHT SYSTEMS INCORPORATING PRISMATIC STRUCTURES AND LIGHT REDIRECTORS
Apparatus and method for collecting and directing light from a source via a light guide and modulated display assembly in an efficient manner through the design and use of prismatic optical structures, diffusers and/or light redirectors. The prismatic optical structures may include a plurality of rear-facing prisms and/or front-facing prisms, each with an associated prism apex angle. The prism apex angle for each of the prisms may be selected such that on-axis brightness intensity and/or total optical power extraction of the display are improved.
1 . A display apparatus comprising;
an array of light modulators defining a display surface;
a light guide having front and rear surfaces and a plurality of geometric light redirectors;
a rear-facing plurality of prisms,
a front-facing plurality of prisms, wherein each of the rear-facing and front-facing plurality of prisms is located between the light guide and the display surface, and wherein an apex angle of one of the rear-facing plurality of prisms and the front-facing plurality of prisms is less than or equal to about 75 degrees or greater than or equal to about 105 degrees.
2 . The display of claim 1 , wherein the front-facing plurality of prisms form a front-facing prism sheet, and the rear-facing plurality of prisms form a rear-facing prism sheet.
3 . The display of claim 2 , wherein the apex angles of one of the rear-facing prisms and the front-facing prisms are constant across the respective prism sheet.
4 . The display of claim 2 , wherein the apex angles of one of the rear-facing prisms and the front-facing prisms vary across the respective prism sheet.
5 . The display of claim 2 , wherein the apex angles of one of the rear-facing prisms and the front-facing prisms are symmetric across the respective prism sheet.
6 . The display of claim 2 , wherein the apex angles of one of the rear-facing prisms and the front-facing prisms are asymmetric across the respective prism sheet.
7 . The display of claim 2 , further comprising a diffuser located between the rear-facing and front-facing prism sheets.
8 . The display of claim 1 , wherein the plurality of front-facing prisms and the plurality of rear-facing prisms form opposing sides of a single prism sheet.
9 . The display of claim 1 , wherein the front and rear facing prisms are contained entirely within an optical cavity.
10 . The display of claim 1 , wherein the apex angle of the rear-facing plurality of prisms is between about 105 and 130 degrees.
11 . The display of claim 1 , wherein the apex angle of the rear-facing plurality of prisms is between about 60 and 75 degrees.
12 . The display of claim 1 , wherein the apex angle of the front-facing plurality of prisms is between about 105 and 130 degrees.
13 . The display of claim 1 , wherein the apex angle of the front-facing plurality of prisms is between about 60 and 75 degrees.
14 . The display of claim 1 , wherein the apex angle of the front-facing plurality of prisms is greater than about 130 degrees.
15 . The display of claim 1 , wherein the apex angle of the rear-facing plurality of prisms is less than about 60 degrees.
16 . The display of claim 1 , wherein the light modulators are MEMS light modulators.
17 . The display of claim 1 , wherein the light modulators are shutter-based light modulators.
18 . The display of claim 1 , wherein the light modulators are liquid crystal light modulators.
19 . The display of claim 1 , further comprising a lamp for injecting light into the light guide.
20 . The display of claim 1 , wherein the apex angle of the rear-facing plurality of prisms is substantially the same as the apex angle of the front-facing plurality of prisms.
21 . A method of forming an image using a display apparatus comprising:
providing an array of light modulators, which defines a display surface, in proximity to an illumination system including
a front-facing plurality of prisms,
a rear-facing plurality of prisms, wherein an apex angle of one of the rear-facing plurality of prisms and the front-facing plurality of prisms is less than or equal to about 75 degrees or greater than or equal to about 105 degrees, and
a light guide positioned behind the rear-facing plurality of prisms, the light guide having front and rear surfaces and a plurality of geometric light redirectors formed therein;
providing one or more light sources configured to illuminate the light redirectors,
reflecting light off the plurality of light redirectors to within a useful range of angles about a display axis perpendicular to the display surface; and
redirecting the light reflected into the useful range of angles by the light redirectors towards the display surface, by both of the front-facing plurality of prisms and rear-facing plurality of prisms, such that the reflected light remains within the same useful range of angles.
22 . The method of claim 21 , wherein the front-facing plurality of prisms form a front-facing prism sheet, and the rear-facing plurality of prisms form a rear-facing prism sheet.