An optical system for displaying a virtual image to a viewer, comprising: stacked integral first reflective polarizer and integral second reflective polarizer, such that for substantially normally incident light: for at least one visible wavelength in a first wavelength range extending from about 450 nm to about 680 nm, the first reflective polarizer reflects at least 60% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state, and the second reflective polarizer transmits at least 60% of the incident light for each of the first and second polarization states; and for at least one infrared wavelength in a second wavelength range extending from about 900 nm to about 1150 nm, the first reflective polarizer reflects at least 60% of the incident light having the first polarization state and transmits at least 60% of the incident light having the second polarization state, and the second reflective polarizer reflects at least 60% of the incident light having the second polarization state and transmits at least 20% of the light having the first polarization state; and a display and a mirror disposed on a same side of, and generally facing, the stacked first and second reflective polarizers, such that for substantially normally incident light and for the at least one visible wavelength, the mirror reflects at least 80% of the incident light for each of the first and second polarization states, and such that when an image is emitted by the display, the optical system displays a virtual image of the emitted image, after the emitted image is at least once reflected by the stacked first and second reflective polarizers, for viewing by a viewer. for at least one visible wavelength in a first wavelength range extending from about 450 nm to about 680 nm, the first reflective polarizer reflects at least 60% of the incident light having a first polarization state and transmits at least 60% of the incident light having an orthogonal second polarization state, and the second reflective polarizer transmits at least 60% of the incident light for each of the first and second polarization states; and for at least one infrared wavelength in a second wavelength range extending from about 900 nm to about 1150 nm, the first reflective polarizer reflects at least 60% of the incident light having the first polarization state and transmits at least 60% of the incident light having the second polarization state, and the second reflective polarizer reflects at least 60% of the incident light having the second polarization state and transmits at least 20% of the light having the first polarization state; and a display and a mirror disposed on a same side of, and generally facing, the stacked first and second reflective polarizers, such that for substantially normally incident light and for the at least one visible wavelength, the mirror reflects at least 80% of the incident light for each of the first and second polarization states, and such that when an image is emitted by the display, the optical system displays a virtual image of the emitted image, after the emitted image is at least once reflected by the stacked first and second reflective polarizers, for viewing by a viewer.