Electrically-actuated variable transmission film having very low haze and a visible grid in a clear state
A light attenuator that provides transparent light states and absorbing dark states for use in selectively controlling light, especially for smart glass applications. The light attenuator includes abutting areas of attenuation and transparency that form a repeat pattern or a quasi-repeat pattern. The attenuating areas are visible when the light attenuator is in the light state, but the repeat pattern is sufficiently large that a viewer looks through the attenuator and sees no haze.
1. A light attenuator comprising:
a first transparent substrate;
a second transparent substrate;
a first transparent electrode adjacent the first transparent substrate;
a second transparent electrode adjacent the second transparent substrate,
a transparent polymer structure disposed between the first transparent electrode and the second transparent electrode, the transparent polymer structure defining a volume between the first transparent electrode and the second transparent electrode; and
an electrophoretic ink disposed in the volume, the electrophoretic ink comprising charged light-scattering particles dispersed in a transparent fluid,
wherein the charged light-scattering particles are responsive to electric fields applied between the first and second transparent electrodes, and with the application of electric fields the charged light-scattering particles move between:
a first state in which the charged light-scattering particles are distributed throughout the volume, thereby scattering light incident on the light attenuator, and
a second state in which the charged light-scattering particles are concentrated within locations in the transparent polymer structure, thereby removing the charged light-scattering particles from a path of light passing through the light attenuator, thereby providing visible transmission for the light between the first and second transparent substrates,
wherein the locations in the transparent polymer structure include a color mask, such that, in the second state, diffuse reflection from the concentrated charged light-scattering particles are reduced compared to concentrated charged light-scattering particles at locations in the transparent polymer structure without the color mask.
2. The light attenuator of claim 1 , wherein the color mask is applied to a top side and a bottom side of the locations in the transparent polymer structure.
3. The light attenuator of claim 1 , wherein the electrophoretic ink additionally comprises charged light-attenuating particles, wherein the electrophoretic mobility of the charged light-scattering particles and the charged light-attenuating particles are different.
4. The light attenuator of claim 3 , wherein the light-attenuating particles have a higher electrophoretic mobility than the light-scattering particles.
5. The light attenuator of claim 4 , wherein the majority of the particles in the electrophoretic ink are light-scattering particles.
6. The light attenuator of claim 3 , wherein the light-attenuating particles are black and the light-scattering particles are white.
7. The light attenuator of claim 1 , wherein the transparent polymer structure includes walls that divide the volume into a monolayer of discrete cavities comprising the walls and filled with the electrophoretic ink.
8. The light attenuator of claim 7 , further comprising a sealing layer to retain a portion of the electrophoretic ink inside each discrete cavity.
9. The light attenuator of claim 7 , wherein at least a portion of the walls are colored to match the charged light-scattering particles.
10. The light attenuator of claim 7 , wherein at least a portion of the walls are colored black or another dark color.
11. The light attenuator of claim 1 , incorporated into one of: a window, a mirror, a light shutter, a light modulator, a variable light transmittance sheet, a variable light reflectance sheet, an electrophoretic sun visor for a vehicle, or a see-through display.