1.  Field of the Invention
The present invention relates to a light source device to which an endoscope and an image processing device can be connected and an endoscope system having an image processing device and a light source device and to which an endoscope can be connected. 
2.  Description of the Related Art
Endoscope devices have been recently used in the medical field and the industrial field.  In the medical field, the endoscope is used for observation of organs in a body cavity, for example, and therapeutic treatments using a treatment instrument as necessary.  Also, in the industrial field, the endoscope is used for observation and inspection of internal scratches, corrosions and the like in a boiler, a turbine, an engine, a chemical plant and the like. 
Some of these endoscope devices are provided with automatic light control means for automatically controlling the brightness of a subject image to be observed.  The automatic light control means includes various types, but a type controlling an illumination light amount according to the brightness of the subject image to be observed is one example.  Also, when the endoscope device is an electronic endoscope for capturing a subject image by an image pickup device, a device shutter method for controlling the brightness by controlling an accumulation time of charge coupled device as an image pickup device may be employed. 
The device shutter method controls the brightness of an image by driving of the image pickup device and is capable of capturing an image with a desired brightness without controlling the light amount of the illumination light.  Therefore, in the device shutter method, regardless of the light amount of the illumination light, the illumination light enters the endoscope as it is.  This also applies to a case where the light amount of the illumination light is set at the maximum, for example. 
Then, Japanese Unexamined Patent Application Publication No.  2000-75220, for example, describes an endoscope light source device which can limit the maximum light amount of illumination light incident to an endoscope when a video signal processing device having the device-shutter type automatic light control means is connected. 
However, the endoscope light source device described in the above Japanese Unexamined Patent Application Publication No.  2000-75220 can not receive information on brightness of an image from the video signal processing device in case of defective connection occurring with the video signal processing device and thus, the light amount of the illumination light can not be controlled appropriately.  As a result, there is a possibility that an excessively small (minimum, for example) light amount of the illumination light enters the endoscope or an excessively large (maximum, for example) light amount of the illumination light enters the endoscope.