Rear projection image viewing system

• US 4,721,361 A
• Filed: 06/17/1987
• Issued: 01/26/1988
• Est. Priority Date: 01/28/1986
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: van de Ven, Johannes C.
• Primary Examiner(s): Wintercorn, Richard A.
• Application Number:
  US07/063,739
• Time in Patent Office: 223 Days
• Field of Search: 350/124, 350/127, 350/128, 353/74, 353/75, 353/77, 352/104, 355/45
• US Class Current: 359/457
• CPC Class Codes: G03B 21/625 Lenticular translucent screens

Abstract

A rear-projection system by means of which a high brightness and contrast can be obtained in that the projection screen has a maximum transmission for signal light and ambient light. This is achieved by making the surfaces of the projection-screen anti-reflecting as far as possible. A satisfactory contrast is further guaranteed by ensuring that ambient light which has traversed the screen is absorbed in dark layers inside the enclosure. Further steps may be taken in order to prevent ambient light which is incident on the mirror from being reflected back to the screen.

Claims

1. In a rear projection system comprising:

an enclosure having an opening;

a rear projection screen connected to said enclosure and having a rear surface and a front surface, for transmitting light impinging on said rear surface to said front surface, said light passing through said opening, wherein said screen includes means for diffusing said light and is arranged such that at least a portion of ambient light impinging on said front surface is transmitted into said enclosure; and

at least one image source and at least one projection device in said enclosure, said projection device being arranged to project light from said image source onto said rear surface;

the improvement wherein said rear projection screen has a maximum transmissivity for said ambient light;

said rear projection screen further has at least one anti-reflecting surface; and

said system includes means for preventing ambient light, transmitted through said screen, from being reflected back onto said anti-reflecting surface.

2. A system as claimed in claim 1, wherein said means for diffusing comprises a first sheet having light-diffusing elements, and said screen comprises a second sheet with a surface having a Fresnel-lens structure;

and

wherein at least one surface of said first sheet and at least one surface of said second sheet are anti-reflecting surfaces.

3. A system as claimed in claim 2, wherein the anti-reflecting surface of said second sheet has a micro-relief structure having height differences and distances between peaks of the order of 200 to 800 nm.

4. A system as claimed in claim 3, wherein said micro-relief structure is formed in a layer of an ultraviolet-curable material.

5. A system as claimed in claim 2, wherein at least one of the anti-reflecting surfaces is a mechanically roughened surface having a roughened profile coated with a thin layer of constant thickness conforming to said profile.

6. A system as claimed in claim 2, wherein at least one of said anti-reflecting surfaces is a surface roughened by ion-implantation and etching.

7. A system as claimed in claim 2, wherein light from said image source travels along a predetermined path to said projection screen;

said device comprises at least one mirror for folding said light path, and

said means for preventing comprises light absorbing blinds arranged between said screen and said mirror.

8. A system as claimed in claim 7, wherein said Fresnel-lens structure has upright sides;

and

said blinds comprise light-absorbing material deposited on said upright sides.

9. A system as claimed in claim 8, wherein said Fresnel-lens structure is formed on the front surface of said second sheet.

10. A system as claimed in claim 1, wherein said projection device comprises a projection lens, and at least one surface of said projection lens has a micro-relief structure having height differences and distances between peaks of the order of 200 to 800 nm.

11. A system as claimed in claim 1, wherein said projection screen comprises a single sheet having a front surface and a rear surface;

and wherein said anti-reflecting surface is said rear surface.

12. A system as claimed in claim 1, wherein light travels from said image source to said projection screen along a predetermined light path;

said rear projection system comprises light reflecting elements situated outside of said light path; and

said means for preventing comprises matte-black fiber-loaded material applied to said elements, whereby said elements are made light absorbing.

13. A system as claimed in claim 1, wherein light travels along a predetermined light path from said image source to said projection screen;

further comprising at least one mirror for folding said light path and for reflecting ambient light, diffused toward said mirror by said rear projection screen, away from said rear projection screen.

14. In a rear projection system comprising:

an enclosure having an opening;

a rear projection screen connected to said enclosure and having a rear surface and a front surface, for transmitting light impinging on said rear surface to said front surface said light passing through said opening, wherein said screen includes means for diffusing said light and is arranged such that at least a portion of ambient light impinging on said front surface is transmitted into said enclosure; and

at least one image source and at least one projection device in said enclosure, said projection device being arranged to project light from said image source along a path onto said rear surface;

the improvement wherein said rear projection screen has a maximum transmissivity for said ambient light, and includes at least one anti-reflecting surface; and

wherein said system includes light absorbing surfaces for absorbing ambient light transmitted through said screen, said surfaces covering substantially all elements of the system disposed outside said light path which are positioned such that said elements could reflect ambient light transmitted through the screen.

15. A system as claimed in claim 14, wherein said light absorbing surfaces are formed by matte black fiber loaded material applied to said elements.

16. A system as claimed in claim 14, further comprising at least one mirror for folding said light path and for reflecting ambient light, diffused toward said mirror by said screen, away from said screen.

17. A system as claimed in claim 14, wherein

said device comprises at least one mirror for folding said light path, and

said system comprises light absorbing blinds arranged between said screen and said mirror.