In recent years, there has been proposed a variable light distribution headlight that can automatically change the light distribution thereof according to the running status of a vehicle. A headlight obtained by combining an LED and a liquid crystal shutter is known as such a variable light distribution headlight. However, in the illumination device obtained by combining an LED and a liquid crystal shutter, the LED is a diffusion light source having a large area. Therefore, it is impossible to finely control the light distribution with a refraction/reflection optical system, and it is difficult to deliver a light beam over a long distance. Furthermore, since the LED has a lower emission intensity than the conventional lamp light source, it is necessary to arrange a large number of LEDs in order to obtain a large light quantity as a headlight. This arrangement is expensive and requires a large installation space. Also, with a configuration in which a large number of high-intensity LEDs are arranged, it is necessary to take some measures for heat dissipation.
Patent Literature 1 discloses a vehicle lamp including a light source that emits a coherent light beam, and a hologram device storing a hologram pattern. The hologram pattern has been calculated such that a diffracted light beam reproduced by irradiation with the coherent light beam forms a light distribution pattern for the vehicle lamp with a predetermined light intensity distribution.
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