Conventionally, a liquid crystal display device which carries out a full-color display achieves a full-color display by (i) dividing each pixel of a transmissive liquid crystal display element into three picture elements, (ii) attaching red (R), green (G), and blue (B) color filters to the respective three picture elements, (iii) irradiating the three picture elements with white light from a backlight, and (iv) controlling, according to a signal representing a voltage applied to a liquid crystal cell of each picture element, the transmittance of the white light passing through that picture element.
However, since each of the R, G, and B color filters transmits light of wavelengths in its corresponding wavelength range and absorbs light of wavelengths in the other wavelength ranges, such a liquid crystal display device which uses color filters loses approximately ⅔ of the light. This causes efficiency in the utilization of light to be low.
In order to address such a problem, there has been proposed a technique that achieves improvement of efficiency in the utilization of light as disclosed in, for example, Patent Literature 1. FIG. 12 is a cross-sectional view schematically illustrating a configuration of an image display device disclosed in Patent Literature 1. The image display device 21 includes a backlight source 2, a diffraction grating 3, a first microlens array 4, a liquid crystal panel 5, a second microlens array 22, and a diffusion plate 6, which are arranged in this order. The backlight source 2 emits beams of white light W, the beams being substantially parallel to each other. The parallel beams are slightly inclined at an angle to a light-exit surface 12 of a light guide plate 7. The parallel beams, which have entered the diffraction grating 3, are diffracted by the diffraction grating 3. Of the beams of light diffracted by the diffraction grating 3, a first order diffracted beam exits the diffraction grating 3 in a direction substantially vertical to the diffraction grating 3. Note here that, since beams of light of different wavelengths have different angles of diffraction, the first order diffracted beam is separated by color, i.e., into red light R, green light G, and blue light B.
The first microlens array 4 is arranged such that each microlens 4a corresponds to a group of pixels 14, that is, three adjacent pixels of the liquid crystal panel 5. Therefore, the microlenses 4a cause the red light R, the green light G and the blue light B, which have exited from the diffraction grating 3 such that their optical axes are in different directions, to be converged onto respective different pixels 14 of a single group. It is thus possible to cause the red light R, the green light G, and the blue light B to be transmitted or blocked, independently, by controlling each of the pixels 14 to be turned ON/OFF. This allows the image display device 21 to carry out a color display.
Further, the second microlens array 22 is arranged such that microlenses 22a correspond to the respective microlenses 4a of the first microlens array 4, and that a distance L from a main plane of the first microlens array 4 to a main plane of the second microlens array 22 is equal to a distance from the focal point of the first microlens array 4 to the focal point of the second microlens array 22. Therefore, although the red light R, green light G and blue light B have respective optical axes different in direction from one another when they have passed through the pixels 14 of the liquid crystal panel 5, the red light R, green light G and blue light B will have their optical axes aligned in parallel to each other by passing through the microlens 22a of the second microlens array 22.
In this circumstance, the red light R, green light G and blue light B which have passed through the second microlens array 22 are diffused by the diffusion plate 6. As illustrated in FIG. 12, the diffused beams of light have respective directivity properties TR, TG, and TB which are equal to each other. This allows prevention of a color shift which can be recognized by a viewer who views the image display device 21 from different directions. It is thus possible to improve efficiency in the utilization of light and viewing angle characteristics of the image display device 21.