Double-sided turning film
View Patent ↗A backlight device for a display comprising (1) a side-lit light source, (2) a light guide plate and (3) a turning film comprising a light entry and a light exit surface comprising lenticular elements on the exit surface and prismatic structures on the entry surface, wherein the average values of the parameters of the features and the thickness of the film are selected to provide a peak output angle of ±10° from normal to the light exit surface of the light guide plate and an optical gain of at least 1.25. Also disclosed are methods of making the turning film and a display incorporating the backlight.
1. A backlight device for display comprising (1) a side-lit light source, (2) a light guide plate, and (3) a turning film comprising melt-extrudable and thermo-formable polymeric material, the turning film comprising prismatic structures on the light entry surface of the film and lenticular elements on the light exit surface of the film, wherein:
(a) the prismatic structures are characterized by an average apex angle (α+β) and an average pitch (Q);
(b) the lenticular elements are characterized by an average pitch (P) and an average radius of curvature (R); and
(c) the prismatic structures and lenticular elements are out of registration by an average amount (X), and
(d) the film has average thickness (T);
provided that said averages are selected to provide a peak output angle of ±10° from normal to the light exit surface of the light guide plate and an optical gain of at least 1.25; and wherein the turning film value derived from the formula
T
P
-
cos
2
(
α
+
β
2
)
sin
(
α
+
β
)
-
(
R
P
-
(
R
P
)
2
-
1
4
)
is in the range from 0 to about 5.5.
2. The device of claim 1 wherein the turning film comprises a polymer selected from the group consisting of carbonate, ester, sulfone, ethersulfone, and cyclo-olefin.
3. The device of claim 1 wherein at least one side of the prismatic structure is curved.
4. The device of claim 1 wherein the lens shape for the lenticular element, in cross section, is acircular.
5. The device of claim 1 wherein the prismatic structures vary in height.
6. The device of claim 1 wherein the turning film has an average pitch values P and Q are equal.
7. The device of claim 1 wherein the turning film apex angle is rounded and the apex has a radius less than about 0.26P.
8. The device of claim 1 wherein the turning film prismatic structures are extended along a serpentine path on the light entry surface.
9. The device of claim 1 wherein the turning film lenticular elements are extended along a serpentine path on the light exit surface.
10. The device of claim 1 wherein the index of refraction of material forming the turning film is in the range from 1.2 to 1.9.
11. The device of claim 1 wherein the average ratio X/P is in the range from about 0.05 to 0.30.
12. A backlight device for a display comprising (1) a side-lit light source, (2) a light guide plate and (3) a turning film comprising a light entry and a light exit surface comprising lenticular elements on the exit surface and prismatic structures on the entry surface, wherein
(a) the prismatic structures are characterized by an apex angle (α+β) and an average pitch (Q);
(b) the lenticular elements are characterized by an average pitch (P) and an average radius of curvature (R); and
(c) wherein the prismatic structures and lenticular elements are out of registration by an average amount X,
(d) the thickness of the film is T;
provided that the averages are selected to provide a peak output angle of ±10° of normal to the light exit surface of the light guide plate and an optical gain of at least 1.25; and wherein the turning film value derived from the formula
T
P
-
cos
2
(
α
+
β
2
)
sin
(
α
+
β
)
-
(
R
P
-
(
R
P
)
2
-
1
4
)
is in the range from 0 to about 5.5.
13. The device of claim 12 wherein, for the turning film, both average pitch values P and Q are equal.
14. The device of claim 12 wherein, for the turning film, the apex angle is rounded and the apex has a radius less than about 0.26P.
15. The device of claim 12 wherein, for the turning film, at least one side of the elongated prismatic structure is curved.
16. The device of claim 12 wherein, or the turning film, the lens shape for the lenticular element, in cross-section, is acircular.
17. The device of claim 12 wherein, for the turning film, the lens shape for the lenticular element, in cross-section, is substantially circular.
18. The device of claim 12 wherein, for the turning film, the ratio R/P is in the range from about 0.9 to 5.
19. The device of claim 12 wherein, for the turning film, the index of refraction for the material forming the turning film is in the range from 1.2 to 1.9.
20. The device of claim 12 wherein, for the turning film, the ratio average of X/P is in the range from about 0.05 to 0.30.
21. The device of claim 12 having a light entry and a light exit surface comprising lenticular elements on the exit surface and prismatic structures on the entry surface, wherein
(a) the prismatic structures are characterized by an apex angle (α+β) and an average pitch (Q);
(b) the lenticular elements are characterized by an average pitch (P) and an average radius of curvature (R); and
(c) wherein the prismatic structures and lenticular elements are out of registration by an average amount X,
(d) the thickness of the film is T;
provided that the averages of the angles and extent out of registration, are such that (α+β) are in the range of 58 to 74° and the extent out of registration is such that ratio X/P is in the range of 0.05 to 0.30.
22. A display comprising the backlight of claim 1 .
23. A display comprising the backlight of claim 12 .