Illumination systems with sloped transmission spectrum front reflector
A backlight ( 10 ) includes a front and back reflectors ( 12,14 ) forming a light recycling cavity ( 16 ) and one or more light source members ( 24 a, 24 b, 24 c ) disposed to emit light into the light recycling cavity. The front reflector ( 12 ) being partially reflective to provide an output illumination area. The front reflector ( 12 ) has a blue sloped transmission spectra, at normal incidence with a range among bin values from 15% to 100%.
1. A backlight comprising:
a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area; and
one or more light sources disposed to emit light into the light recycling cavity;
wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R f hemi , and the back reflector has a hemispherical reflectivity for unpolarized visible light of R b hemi , and R f hemi *R b hemi is at least 0.65;
and wherein the front reflector has a sloped transmission spectra at a view angle of interest Ω, and a backlight intensity spectrum:
T (Ω,λ)/{1− R b hemi (λ)* R f Hemi (λ)}
is substantially neutral across a visible wavelength band.
2. A backlight according to claim 1 , wherein R f hemi *R b hemi is at least 0.75.
3. A backlight according to claim 1 , wherein R f hemi *R b hemi is at least 0.85.
4. A backlight according to claim 1 , wherein the front reflector comprises a polarizer.
5. A backlight according to claim 1 , wherein the front reflector comprises a reflective polarizer.
6. A backlight according to claim 1 , wherein the backlight illuminates a liquid crystal display panel.
7. A backlight according to claim 5 , wherein the front reflector comprises an absorbing polarizer.
8. A backlight comprising:
a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area;
one or more light sources disposed to emit light into the light recycling cavity;
wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R f hemi , and the back reflector has a hemispherical reflectivity for unpolarized visible light of R b hemi , and R f hemi *R b hemi is at least 0.65;
and wherein the front reflector has a sloped transmission spectra at a view angle of interest χ, and a backlight intensity spectrum
T (Ω,λ)/{1− R b hemi (λ)* R f Hemi (λ)}
is substantially blue-sloped across a visible wavelength band.
9. A backlight according to claim 8 , wherein R f hemi *R b hemi is at least 0.75.
10. A backlight according to claim 8 , wherein R f hemi *R b hemi is at least 0.85.
11. A backlight according to claim 8 , wherein the front reflector comprises a polarizer.
12. A backlight according to claim 8 , wherein the front reflector comprises a reflective polarizer.
13. A backlight according to claim 8 , the backlight illuminates a liquid crystal display panel.
14. A backlight according to claim 12 , wherein the front reflector comprises an absorbing polarizer.
15. A backlight comprising:
a front and back reflector forming a light recycling cavity, the front reflector being partially reflective to provide an output illumination area;
one or more light sources disposed to emit light into the light recycling cavity;
wherein the front reflector has a hemispherical reflectivity for unpolarized visible light of R f hemi , and the back reflector has a hemispherical reflectivity for unpolarized visible light of R b hemi , and R f hemi *R b hemi is at least 0.65;
and wherein the front reflector has a sloped transmission spectra at a view angle of interest Ω, and a backlight intensity spectrum
T (,Ωλ)/{1− R b hemi (λ)* R f hemi (λ)}
is substantially red-sloped across a visible wavelength band.
16. A backlight according to claim 15 , wherein R f hemi *R b hemi is at least 0.85.
17. A backlight according to claim 15 , wherein the front reflector comprises a polarizer.
18. A backlight according to claim 15 , wherein the front reflector comprises a reflective polarizer.
19. A backlight according to claim 15 , the backlight illuminates a liquid crystal display panel.
20. A backlight according to claim 18 , wherein the front reflector comprises an absorbing polarizer.