Display backlight including optical film having a transmission peak wavelength greater than an emisssion peak wavelegnth of the backlight

A backlight for providing illumination to a display panel configured to display an image, the backlight comprising:

• an illumination system comprising red light emitting elements and configured to emit a light from an emission surface thereof, the emitted light comprising at least a red light comprising a red emission spectrum comprising a first red emission peak at a first red peak wavelength with a red full width at 70% maximum FWr1;
• and
• an optical film disposed on the red light emitting elements and comprising a plurality of first layers, a plurality of second layers, and at least one spacer layer disposed between the plurality of first layers and the plurality of second layers, the first and second layers numbering at least 10 in total, each of the first and second layers having an average thickness of less than about 500 nm, each of the at least one spacer layer having an average thickness of at least about 5 microns, such that for an incident light incident on the optical film at an incident angle of greater than about 15 degrees and for at least a first polarization state, an optical transmittance of the optical film versus wavelength has a first red-infrared transmittance peak at a first red-infrared peak wavelength greater than about 600 nm with a red-infrared full width at 50% maximum FW′2, wherein the red-infrared full width at 50% maximum FW′2 of the first red-infrared peak wavelength fully encompasses the red full width at 70% maximum FWr1 of The first red peak wavelength, and FW′2/FWr1≥2.

An optical film comprising a plurality of first layers, a plurality of second layers, and at least one spacer layer disposed between the plurality of first layers and the plurality of second layers, the first and second layers numbering at least 50 in total, each of the first and second layers having an average thickness of less than about 500 nm, each of the at least one spacer layer having an average thickness of at least about 5 microns, wherein a scatter plot of layer thickness versus layer number for at least 30 sequentially arranged and numbered first and second layers in the pluralities of first and second layers comprises a first group of scatter points and a remaining group of scatter points separated along a thickness direction, wherein the scatter points in the first and remaining groups lie on respective substantially straight first and second lines, such that when the optical film is disposed on a substantially Lambertian light source that emits light having respective blue, green, and red emission spectra comprising respective blue, green, and red peaks with respective blue, green, and red full width at 70% maximums FWb1, FWg1, and FWr1, respectively, where FWb1 is greater than FWr1 by at least a factor of 2, and FWg1 is greater than FWr1 by at least a factor of 5, then the optical film transmits the emitted light with a color shift of the transmitted light with respect to the light emitted and as a function of a transmitted angle in a plane substantially perpendicular to the optical film, having a main color shift peak at a transmission angle of less than about 10 degrees and a color shift plateau region that is at least 5 degrees wide and lies at transmission angles of greater than about 2 degrees, the main color shift peak having a full width at 80% maximum of greater than about 1 degree, and the color shift across the color shift plateau region varying with a standard deviation of less than about 0.5.