Optical filter comprising a variable transmittance layer
An optical filter comprising a variable transmittance layer having a first spectrum in a dark state, and a second spectrum in a faded state; and a color balancing layer having a third spectrum; each of the first, second and third spectra comprising a visible portion; the first and third spectra combining to provide a dark state spectrum approximating a dark state target color, and the second and third spectra combining to provide a faded state spectrum approximating a faded state target color. The optical filter may further comprise a light attenuating layer. The optical filter may further comprise part of a laminated glass.
1. An optical filter comprising:
a. a variable transmittance layer having a first spectrum in a dark state, and a second spectrum in a faded state; and
b. a spectrally uniform color balancing layer having a third spectrum;
each of the first, second and third spectra comprising a visible portion;
the first and third spectra combining to provide a dark state spectrum approximating a dark state target color; and
the second and third spectra combining to provide a faded state spectrum approximating a faded state target colour.
2. The optical filter of claim 1 wherein the color balancing layer is inboard of the variable transmittance layer.
3. The optical filter of claim 1 further comprising c) a light attenuating layer.
4. The optical filter of claim 3 wherein the light attenuating layer is outboard of the variable transmittance layer.
5. The optical filter of claim 1 wherein the variable transmittance layer comprises a switching material transitionable from a faded state to a dark state when exposed to electromagnetic radiation, and from a dark state to a faded state with application of a voltage.
6. The optical filter of claim 1 wherein the electromagnetic radiation is UV light.
7. The optical filter of claim 1 wherein the electromagnetic radiation has a component with a wavelength of 450 nm or less.
8. The optical filter of claim 1 wherein the electromagnetic radiation has a component with a wavelength of between 400 and 450 nm.
9. The optical filter of claim 1 wherein the voltage applied is from about 1.1 to about 2.5 V, or any amount or range therebetween.
10. The optical filter of claim 1 further comprising an infrared (IR)-blocking layer, an ultraviolet (UV) blocking layer, or a UV blocking layer and an IR blocking layer.
11. The optical filter of claim 10 wherein the UV blocking layer blocks light with a wavelength of about 370 nm or less, about 400 nm or less, about 420 nm or less or about 435 nm or less.
12. The optical filter of claim 1 comprising any one or more of:
a. an LT A in a dark state of less than about 15%;
b. an LT A in a faded state of greater than about 5%; and
c. a contrast ratio of at least 5.
13. The optical filter of claim 1 comprising a light transmission value of 1% or less in the dark state and 6% or higher in the light state.
14. The optical filter of claim 1 comprising a light transmission value of 5% or less in the dark state and 15% or higher in the light state.
15. The optical filter of claim 1 wherein the target color of the dark state and color of the optical filter in the dark state provide a delta C value of from about 0 to about 20.
16. The optical filter of claim 1 wherein the target color of the dark state and color of the optical filter in the dark state provide a delta E value of from about 0 to about 20.
17. The optical filter of claim 1 wherein the target color of the faded state and color of the optical filter in the faded state provide a delta C value of from about 0 to about 20.
18. The optical filter of claim 1 wherein the target color of the faded state and color of the optical filter in the faded state provide a delta E value of from about 0 to about 20.
19. A device comprising the optical filter of claim 1 , wherein the device is a laminated glass, an ophthalmic device, an automotive glazing product or an architectural glazing product; optionally the automotive glazing product comprises a sunroof.
20. A method of preparing an optical filter approximating a target color, comprising:
a. providing a variable transmittance layer having a first spectrum in a dark state, and a second spectrum in a faded state;
b. selecting a spectrally uniform color balancing layer having a third spectrum; and
c. combining the variable transmittance layer and color balancing layer in a stack approximating the target color in the faded state, the dark state or both the faded state and the dark state.