Optical filter and lighting device to reproduce the light of the sky and the sun comprising the same

Optical filter (100,100′,100″,100′″) according to any one of the preceding claims, wherein the second element of optically non-transparent material (109,109′) comprises

• an element of absorbing or reflective material covering and/or constituting at least a portion of the entry surface and/or of the exit surface not comprising the portions overlapping the entry (104) and exit (105) faces of the channels (103);
• and/or
• a second optically absorbing material that at least partially fills the plurality of defined interspaces between adjacent channels;
• and/or
• a second optically absorbing material having absorption coefficient ensuring an absorption of at least 50%, preferably at least 80%, more preferably at least 90% of the visible light for a thickness equal to 1/5, preferably 1/10 of the length of the channels (103).

Filter (100,100′,100″,100′″) according to any one of the preceding claims, wherein said filter (100) comprises a plurality of channels (103) characterized by:

• a distribution of channels which are statistically equivalent to each other;
• and/or
• a distribution of channels with an averagely circular section;
• and/or
• a distribution of channels having section substantially not equal between them;
• and/or
• a distribution of channels having a substantially non-circular section.

Optical filter (100,100′,100″,100′″) comprising

• a substantially flat entry surface (101),
• a substantially flat exit surface (102) parallel to the entry surface,
• a plurality of channels (103) made of a material substantially transparent to light, wherein the channels (103) of the plurality of channels
• comprise an entry face (104), an exit face (105) and a lateral surface extending perimetrically between the entry face (104) and the exit face (105) over a length (L) of the channels (103),
• are arranged side by side and parallel to each other, so as to define a plurality of interspaces between adjacent channels (103),
• have a channel axis (Y) incident to the entry (101) and exit (102) surface, and
• are arranged with the entry face (104) substantially overlapping the entry surface (102) and with the exit face (105) substantially overlapping the exit surface (102),
• at least one element of optically absorbing or non-transparent material (108,109;109′) configured and arranged with respect to the channels (103) so as to reduce the passage of light between adjacent channels (103) of the plurality of channels and so as to reduce the passage of light parallel to and externally to the channels, or
• at least one first element of optically absorbing material (108) configured and arranged with respect to the channels (103) so as to reduce the passage of light between adjacent channels (103) of the plurality of channels (103), and at least one second element of optically non-transparent material (109;109′) configured and arranged with respect to the channels (103) so as to prevent the passage of light parallel to the channels (103) and externally thereto through the interspaces between adjacent channels (103);
• wherein the channels (103) have a refractive index whose value decreases starting from a maximum refractive index (na) along a radially outward direction away from the channel axis (Y) passing through a centre of gravity of a section of the respective channel (103), so as to define a radial profile of refractive index of the channels, and/or
• wherein the radial profile of refractive index of the channels (103) is configured such that the optical filter (100,100′,100″,100′″) has an image plane and an object plane, at least one between the object plane and the image plane being placed at a distance (D) from the entry surface (101) and/or from the exit surface (102), the distance (D) being comprised between 0.5 D1 and 2 D1, with D1 being a nominal distance given by a relation comprised in the group consisting of:
• D
• 1
• ≃
• 2
• ⁢
• L
• n
• a
• ⁢
• π
• D
• 1
• ≃
• 2
• .
• 4
• ⁢
• 1
• ⁢
• L
• n
• a
• ⁢
• a
• D
• 1
• ≃
• 4
• ⁢
• L
• n
• a
• ⁢
• π
• .

Optical filter (100,100′,100″,100′″) comprising

• a substantially flat entry surface (101),
• a substantially flat exit surface (102) parallel to the entry surface,
• a plurality of channels (103) made of a material substantially transparent to light, wherein the channels (103) of the plurality of channels
• comprise an entry face (104), an exit face (105) and a lateral surface extending perimetrically between the entry face (104) and the exit face (105) over a length (L) of the channels (103),
• are arranged side by side and parallel to each other, so as to define a plurality of interspaces between adjacent channels (103),
• have a channel axis (Y) incident to the entry (101) and exit (102) surface, and
• are arranged with the entry face (104) substantially overlapping the entry surface (102) and with the exit face (105) substantially overlapping the exit surface (102),
• at least one element of optically absorbing or non-transparent material (108,109;109′) configured and arranged with respect to the channels (103) so as to reduce the passage of light between adjacent channels (103) of the plurality of channels and so as to reduce the passage of light parallel to and externally to the channels, or
• at least one first element of optically absorbing material (108) configured and arranged with respect to the channels (103) so as to reduce the passage of light between adjacent channels (103) of the plurality of channels (103), and at least one second element of optically non-transparent material (109;109′) configured and arranged with respect to the channels (103) so as to prevent the passage of light parallel to the channels (103) and externally thereto through the interspaces between adjacent channels (103);
• wherein the channels (103) have a refractive index whose value decreases starting from a maximum refractive index (na) along a radially outward direction away from the channel axis (Y) passing through a centre of gravity of a section of the respective channel (103), so as to define a radial profile of refractive index of the channels, and/or
• wherein the radial profile of refractive index of the channels (103) is configured such that each channel (103) of the plurality of channels behaves substantially as a converging lens having optical axis coincident with a channel axis and a focal length (f) in the medium satisfying the relation 0.5 f′<f<2f′, preferably 0.7 f′<f<1.6f′, more preferably 0.7 f′<f<1.4f′, even more preferably 0.9 f′<f<1.2f′, with f′≃L, or f′≃2L.