Direct-lit backlight with angle-dependent birefringent diffuser
Assignee3M Innovative Properties Company
InventorsMark B. O'Neill, Carl A. Stover, Michael F. Weber
Life of this patent
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Abstract
A direct-lit backlight includes a diffuse reflector disposed in front of a light source. The diffuse reflector has a continuous phase material and a disperse phase material, at least one of which is birefringent, and the disperse phase material is formed into particles having a transverse dimension less than 1 micrometer for efficient visible light scattering. The continuous and disperse phases have refractive indices tailored so the diffuse reflector transmits light from the light source substantially more strongly for obliquely incident light than for normally incident light to provide bulb-hiding characteristics.
Claims21
A direct-lit backlight, comprising:
- a light source;
- and
- a diffuse reflector disposed in front of the light source, and having a continuous phase material and a disperse phase material, at least one of which is birefringent, and whose refractive indices are tailored to provide the diffuse reflector with a transmissivity that increases substantially with increasing incidence angle from normal incidence.
A combination of optical films suitable for use in a direct-lit backlight, the combination comprising:
- a diffuse reflective polarizer having a continuous phase material and a disperse phase material, at least one of which is birefringent, and whose refractive indices are tailored to provide the diffuse reflective polarizer with a transmissivity along a block axis thereof that increases substantially with increasing incidence angle from normal incidence;
- and
- a second polarizer having a block axis and a pass axis, the second polarizer being oriented such that the pass axis of the second polarizer is aligned with the block axis of the diffuse reflective polarizer.
Dependencies are inferred from the claim text.