Luminaire with a light diffuser

1. A luminaire comprising:

a light source;

an exit window for light from the light source; and

a diffuser at the exit window for diffusing the light,

wherein the diffuser comprises a plurality of micro-optical elements, each micro-optical element adapted to redirect light from the light source, so that the redirected light from each element emerges from the diffuser at a respective predetermined polar angle,

wherein the plurality of micro-optical elements comprises first micro-optical elements, which redirect light from the light source into a first range of polar angles,

wherein the first optical elements occupy a greater proportion of the area of the diffuser in a first neighbourhood than in a second neighbourhood,

wherein the first neighbourhood receives less light from the light source than the second neighbourhood and a local density of the first optical elements is proportional to the reciprocal of the luminous emittance at the exit window,

wherein the plurality of micro-optical elements further comprises second micro-optical elements, which redirect light from the light source into a second range of polar angles,

wherein the polar angles of the first range are greater than the polar angles of the second range, and

wherein a spatial distribution of the second optical elements complements a spatial distribution of the first optical elements.

2. The luminaire of claim 1 , wherein a remaining area of the exit window, not covered by the first micro-optical elements, is occupied by second micro-optical elements.

3. The luminaire of claim 2 , wherein the second micro-optical elements occupy a greater proportion of the area of the diffuser in the second neighbourhood than in the first neighbourhood.

4. The luminaire of claim 1 , wherein each micro-optical element comprises at least one of the following micro-optical structures: a free-shape micro-optical lens, a flat facet, a curved surface, and a prismatic micro-structure.

5. The luminaire of claim 1 , wherein for each of a plurality of locations on the diffuser, the proportion of the local area of the diffuser that is covered by the first micro-optical elements is inversely proportional to the luminous emittance at that location.

6. The luminaire of claim 5 , wherein the second range of polar angles is from 0° to an angle alpha and the first range of polar angles is from the angle alpha to 60° or more, wherein alpha is less than or equal to 30°.

7. The luminaire of claim 6 , wherein first micro-optical elements of greater area are provided in the first neighbourhood, compared with the second neighbourhood.

8. The luminaire of claim 7 , for each of a plurality of locations on the diffuser, the proportion U:

U

=

1

-

l

ma

⁢

⁢

x

-

l

m

⁢

⁢

i

⁢

⁢

n

l

ma

⁢

⁢

x

+

l

m

⁢

⁢

i

⁢

⁢

n

wherein l max and l min are the maximum and minimum values, respectively, of luminous emittance measured over the different locations in the exit window.

9. The luminaire of claim 1 , wherein, in each micro-optical element, there is at least one facet, which is adapted to redirect the light by at least one of: refraction; and total internal reflection.

10. The luminaire of claim 1 , wherein the diffuser is arranged so that the light from the light source arrives at the diffuser in a direction substantially normal to the diffuser.

11. The luminaire of claim 1 , wherein the micro-optical elements are provided on a surface of the diffuser facing the light source.

12. The luminaire of claim 1 , wherein the micro-optical elements are provided on a surface of the diffuser facing away from the light source.

13. The luminaire of claim 1 , wherein the redirected light emerges from each micro-optical element at a predetermined azimuthal angle, wherein the distribution of light over a predetermined range of azimuthal angles is substantially the same for neighbourhoods at different locations on the diffuser.

14. A method of designing and manufacturing a diffuser for a luminaire, the luminaire comprising a light source; and an exit window for light from the light source, the diffuser being suitable for diffusing the light at the exit window,

wherein the diffuser comprises a plurality of micro-optical elements, each micro-optical element adapted to redirect light from the light source, so that the redirected light from each element emerges from the diffuser at a respective predetermined polar angle,

the method comprising:

determining the luminous emittance at the exit window;

assigning at least some of the plurality of micro-optical elements as first micro-optical elements, which redirect light from the light source into a first range of polar angles;

distributing the first micro-optical elements such that, for each of a plurality of locations on the diffuser, the proportion of the local area of the diffuser that is covered by the first micro-optical elements is inversely proportional to the luminous emittance at that location;

assigning at least some of the plurality of micro-optical elements as second micro-optical elements such that a spatial distribution of the second optical elements complements a spatial distribution of the first optical elements, which second micro-optical elements redirect light from the light source into a second range of polar angles wherein the polar angles of the first range are greater than the polar angles of the second range; and

manufacturing the diffuser so designed.