1. Technical Field
The present invention relates to an illumination device and a projector. In particular, the present invention relates to an illumination device used for a projector.
2. Related Art
A liquid crystal display device or a digital micromirror device (DMD) that is used for a spatial light modulation device in a projector has a characteristic in that luminance of an image is substantially regulated during one frame period of an image signal.
In the case in which a hold-type spatial light modulation device is used, a motion image response may be degraded due to a motion image blurring occurring at the time at when motion images are displayed.
In order to desirably obtain the motion image response, an impulse-type display method can be applied, in that a display light is generated during a period sufficiently shorter than the one frame period.
In the case of the hold-type spatial light modulation device, the impulse-type display method is performed by controlling the spatial light modulation device or by intermittent illumination that intermittently applies illumination light.
In such impulse-type display methods, the impulse-type display method due to the intermittent illumination is excellent in that the efficiency of illumination is not degraded and the dynamic range of the spatial light modulation device is not narrow.
Conventionally, as disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. 2000-275604 and Japanese Unexamined Patent Application, First Publication No. 2004-325576, the technique in which the impulse-type display method is performed by the intermittent illumination of the spatial light modulation device is suggested.
In the technique in Japanese Unexamined Patent Application, First Publication No. 2000-275604, back lights formed on each illumination region are controlled so as to illuminate or turn off.
In this technique, there is an advantage in that it is possible to improve the motion image response due to controlling the illumination light.
In the case of using back lights, it is difficult to adjust each of the back lights in which the dispersion of the amount of illumination or deterioration of illumination with time occur.
In an optical system including a light source and a spatial light modulation device, a special expansion in a space in which a luminous flux exists is shown by the product of the emission area and radiation angle (etendue, Geometrical Extent).
Since the etendue is restricted, it is difficult to efficiently utilize the light emitted from the light source depending on increasing the emission area due to arraying the light sources.
In Japanese Unexamined Patent Application, First Publication No. 2004-325576, the illumination light is scanned onto a projection surface of the spatial light modulation device.
In the impulse-type display method, though the motion image response can be improved, a flicker of the images on the display is easily generated.
The flicker is easily noticed by a viewer, especially, in the case of displaying a still image on the display.
In Japanese Unexamined Patent Application, First Publication No. 2004-325576, since it is impossible to select scanning or non-scanning in accordance with images, it is difficult to suppress the occurrence of flicker.
As described above, though a high efficiency of illumination and a desirable motion image response can be obtained, there is the problem in that it is difficult to suppress the occurrence of flicker.