Fresnel lens and lighting apparatus provided with the fresnel lens

• US 20060056185A1
• Filed: 09/14/2005
• Published: 03/16/2006
• Est. Priority Date: 09/16/2004
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Morino, Takeshi, Honguh, Yoshinori, Shiratsuchi, Masataka, Tokuhara, Naoto
• Granted Patent: US 7,618,161 B2
• Time in Patent Office: Days
• US Class Current: 362/332
• CPC Class Codes: F21V 5/045 the lens having discontinuous faces, e.g. Fresnel lenses
• CPC Class Codes: F21W 2131/406 for theatres, stages or film studios
• CPC Class Codes: G02B 3/08 with discontinuous faces, e.g. Fresnel lens diffractive Fresnel lenses G02B5/1876

Abstract

In a Fresnel lens which is made of a lens material whose refraction index is n, and focuses light beam from a light source at a specified radiation view angle φ, and has plural N pieces of circular lens surfaces arranged concentrically around a common optical axis, and plural circular rise surfaces arranged adjacent alternately between these lens surfaces, and two lens surfaces adjacent via at least one of the rise surfaces are concave surfaces, and tangent lines and at the intersecting point with the rise surfaces of the shape of a cross section passing through the optical axis of those lens surfaces intersect at the outside with respect to the optical axis, and when the angle formed between these tangent lines is defined as θ, a relational equation θ≧φ/(2 n N) stands.

Claims

1. A Fresnel lens having an optical axis comprising:

N pieces of Fresnel lens segments which are made of a lens material whose refraction index is n, and arranged concentrically around a common optical axis, configured to project light rays from a light source at a specified radiation view angle φ

to an illumination area, and are made into ridge shapes respectively, wherein

each Fresnel lens segment includes

a lens surface which is curved into a concave surface toward the illumination area, and has a top area and a bottom area;

a rise surface which is arranged between adjacent lens surfaces, and joints with the top area and the bottom area, the top area and a bottom area defining first and second tangent lines contacting the top and bottom areas of the each lens surface in a cross section including the optical axis, respectively, and the angle between these first and second tangent lines being defined as θ

, and an inequality of θ

≧

φ

/(2 n N) being established.

2. The Fresnel lens according to claim 1, wherein the top and bottom areas between the lens surface and the rise surface is rounded.

3. The Fresnel lens according to claim 1, further comprising a convex lens portion on the optical axis.

4. The Fresnel lens according to claim 1, wherein the Fresnel lens comprises a flat surface facing the light source.

5. The Fresnel lens according to claim 1, wherein the Fresnel lens has a form of a substantially meniscus lens, which provided with a circular arc plane on which the top areas of the plural Fresnel lens segments are arranged.

6. The Fresnel lens according to claim 1, wherein the rise surface diffuses the light rays.

7. The Fresnel lens according to claim 1, wherein the Fresnel lens has a rear surface facing the light source, which diffuses the light rays.

8. The Fresnel lens according to claim 7, wherein the rise surface diffuses light rays.

9. A lighting apparatus comprising:

a light source which emits light rays;

a Fresnel lens having an optical axis including;

N pieces of Fresnel lens segments which are made of a lens material whose refraction index is n, and arranged concentrically around a common optical axis, configured to project light rays from the light source at a specified radiation view angle φ

to an illumination area, and are made into ridge shapes respectively, wherein

each Fresnel lens segment includes

a lens surface which is curved into a concave surface toward the illumination area, and has a top area and a bottom area;

a rise surface which is arranged between adjacent lens surfaces, and joints with the top area and the bottom area, the top area and a bottom area defining first and second tangent lines contacting the top and bottom areas of the each lens surface in a cross section including the optical axis, respectively, and the angle between these first and second tangent lines being defined as θ

, and an inequality of θ

≧

+/(2 n N) being established.

10. A lighting apparatus comprising:

a light source which emits light rays;

a Fresnel lens which is made of a lens material whose refraction index is n, and projects light rays from the light source at a specified radiation view angle φ

to an illumination area, and has an optical axis, the Fresnel lens comprising;

a plurality of Fresnel lens segments which are arranged concentrically around a common optical axis, and are made into ridge shapes respectively, wherein

each Fresnel lens segment has

a lens surface which is curved into a concave surface toward the illumination area, and has a top area and a bottom area,

a rise surface which is arranged between adjacent lens surfaces, and joints with the top area and the bottom area, the light rays projected from adjacent lens surfaces irradiating circular band areas having widths, respectively, which mutually overlap at least half of the width of the circular band area.