Light-emitting module with a curved prism sheet

1. A light-emitting module comprising:

a light source array of solid state light-sources arranged along a geometrical line, and

an envelope surrounding the light unit, said envelope comprising:

a base structure extending along the light source array and including a diffuse reflective portion;

two side reflector regions arranged on opposite sides of the base structure; and

a curved prism sheet extending between said two side reflector regions at a constant distance from said geometrical line, said curved prism sheet having an inner concave surface facing the light source array and an outer convex surface facing away from the light source array,

said outer convex surface including a plurality of prism structures having right top angles and arranged such that light emitted from said light sources and directly incident on said prism structures is retroreflected back towards said geometrical line, while light incident on said prism structures after being diffused by said diffuse reflective portion and/or being reflected by said side reflector regions, is transmitted through said curved prism sheet.

2. The light-emitting module according to claim 1 , wherein each side reflector region is a specular reflector.

3. The light-emitting module according to claim 1 , wherein each side reflector region is a semispecular reflector.

4. The light-emitting module according to claim 1 , wherein the light-emitting module further comprises a diffuser arranged between the outer curved prism sheet and the light source array, the diffuser being configured for scattering light in a longitudinal direction of the light-emitting module.

5. The light-emitting module according to claim 4 , wherein the diffuser is an asymmetric diffuser for light scattering along one direction.

6. The light-emitting module according to claim 1 , wherein the envelope is provided in the form of a tubular member.

7. The light-emitting module according to claim 1 , wherein the envelope further comprises at least a side wall extending between the outer curved prism sheet and the base structure, whereby the side reflector region is an integral part of the side wall.

8. The light-emitting module according to claim 7 , wherein the side reflector wall further comprises an outer reflective portion extending beyond the outer convex surface.

9. The light-emitting module according to claim 7 , wherein the side reflector walls are outwardly tilted with respect to said base structure.

10. The light-emitting module according to claim 1 , wherein the inner concave surface is provided with plurality of scattering areas.

11. The light-emitting module according to claim 10 , wherein the scattering areas cover 10-50% of the inner concave surface.

12. The light-emitting module according to claim 1 , wherein the envelope has a constant cross section taken across the longitudinal direction of the light-emitting module.

13. The light-emitting module according to claim 12 , wherein the light sources are arranged on the base structure.

14. A lighting device comprising a light-emitting module according to claim 1 arranged for retrofitting a conventional fluorescent tube.