Patent Publication Number: US-2011051020-A1

Title: Video Projector And Image Display System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2009-199042, filed on Aug. 28, 2009, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a video projector including a plurality of light sources used to display pictures and an image display system including such a video projector. 
     One type of a video projector that projects and displays an image includes a plurality of light sources. For example, when a projector includes two lamps serving as light sources for displaying images, the projector switches the activated one of the two lamps so that the video projector may be used over a long period of time. 
     Japanese Laid-Open Patent Publication No. 2006-39329 describes a video projector that allows the activation period for each of a plurality of light sources to be set. To prolong the life of the light sources without averaging the cumulative activation time of the light sources, the publication describes setting the activation period of a first light source to eleven hours and the activation period of a second light source to one hour. The light sources are alternately activated in a constant pattern in accordance with the activation period settings. 
     Digital signage using an image display device, which is an electronic device, is a form for displaying advertisements or the like in commercial and public facilities, such as shopping malls and movie theaters. Generally, digital signage sequentially presents an audience with a plurality of video contents (e.g., product advertisement or o facility introduction). Video contents presented in such a manner have different time lengths. For example, one video content may run over thirty minutes while another video content runs over one hour. 
     A video projector that displays an enlarged and projected image may be effective when used for the digital signage described above. Particularly, the video projector described above that uses a plurality of light sources may be effective when used for digital signage that requires a video image to be displayed over a long time period. 
     However, in the prior art device, time may be necessary to switch the light sources. Further, in a projection display device such as that described in the above publication, the light sources are switched in a fixed pattern when the video contents are being presented. When the light sources are switched during the presentation of video content, the video content cannot be displayed during the switching. As a result, the video content would be interrupted when switching the light sources. 
     SUMMARY OF THE INVENTION 
     The present invention provides a video projector and an image display system that present video contents without any interruptions when switching light sources. 
     One aspect of the present invention is a video projector including a plurality of light sources used to display an image and a control unit that switches each of the light sources between states of activation and deactivation. The control unit is capable of setting an activation period for each activation of at least one of the light sources. 
     A further aspect of the present invention is a video projector including a plurality of light sources used to display an image and a control unit that switches each of the light sources between states of activation and deactivation. The control unit sets an activation period for each of the light sources in accordance with a reproduction period of the displayed image. 
     Another aspect of the present invention is an image display system provided with a video projector including a plurality of light sources used to project and display an image and a controller that controls the video projector so as to switch each of the light sources between states of activation and deactivation in accordance with the displayed image. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. In the drawings, like numerals are used for like elements throughout: 
         FIG. 1  is a schematic block diagram of an image display system according to a first embodiment; 
         FIG. 2  is a schematic block diagram of a computer shown in  FIG. 1 ; 
         FIG. 3  is a schematic block diagram of the projector shown in  FIG. 1 ; 
         FIG. 4  is a schematic block diagram of a lamp unit of the projector shown in  FIG. 3 ; 
         FIG. 5  is a schematic flowchart of a setting process for an activation program executed by the projector; 
         FIG. 6  is a table showing one example of a program list including a lamp activation pattern; 
         FIG. 7  is a schematic flowchart of a setting process for a repeat pattern performed by the projector; 
         FIG. 8  is a table showing one example of a repeat list including a repeat pattern; 
         FIG. 9  is a schematic flowchart of a lamp switching control executed by the projector in the first embodiment; 
         FIG. 10  is a schematic flowchart of a repeating process executed during the lamp switching control shown in  FIG. 9 ; 
         FIG. 11  is a schematic block diagram of an image display system according to a second embodiment; 
         FIG. 12  is a schematic block diagram of a vide reproduction device shown in  FIG. 11 ; 
         FIG. 13  is a schematic flowchart of a control program in a remote control mode executed by a computer in the second embodiment; 
         FIG. 14  is a table showing one example of a program list generated by the control program of  FIG. 13 ; 
         FIG. 15  is a schematic flowchart of a setting process for an activation program executed by the projector in the second embodiment; 
         FIG. 16  is a table showing one example of a program list stored in a memory of the projector; 
         FIG. 17  is a schematic flowchart of the operation of the video reproduction device that outputs a video signal in the second embodiment; and 
         FIG. 18  is a schematic flowchart of a lamp switching control executed by the projector in the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     Referring to  FIG. 1 , an image display system according to a first embodiment includes a computer  1 , which serves as a controller, and a projector  2 , which serves as a video projector. The image display system according to the first embodiment will now be discussed with reference to  FIGS. 1 to 10 . 
     As shown in  FIG. 2 , the computer  1  includes a control unit  11 , a memory  12 , a video signal output unit  13 , an operation unit  14 , a display unit  15 , and a control signal input/output unit  16 . The control unit  11  controls various functional units in the computer  1 . The memory  12  stores information such as programs. The video signal output unit  13  outputs video signals. The operation unit  14  is operated by a user. The display unit  15  displays an image. The control signal input/output unit  16  inputs and outputs control signals. The computer  1 , which includes these elements, is formed by a personal computer (PC), which is a versatile electronic device. 
     The control unit  11  is an integrated circuit that outputs control signals or the like to the functional units of the computer  1 . The control unit  11  is formed by, for example, a central processing unit (CPU) and executes a program stored in the memory  12  to generate signals for controlling the functional units of the computer  1 . 
     The memory  12  may be a hard disk drive or a flash memory. The memory  12  stores information for images displayed by the projector  2  and information for controlling the projector  2  in addition to programs executed by the control unit  11 . 
     The video signal output unit  13  includes a High-Definition Multimedia Interface (HDMI) terminal and a Video Graphics Array (VGA) terminal, which output video signals from the computer  1  to an external device. The information of an image stored in the memory  12  and the information of an image displayed on the display unit  15  are provided as video signals from the video signal output unit  13  to the projector  2 . 
     The operation unit  14  includes, for example, a keyboard and a mouse, which are operated by the user. When the operation unit  14  is operated, the control unit  11  receives various types of signals, and the control unit  11  executes control in accordance with the operation contents of the operation unit  14 . 
     The display unit  15  displays an image for the user of the computer  1 . The display unit  15  displays an image based on the video signal output from the video signal output unit  13 . Accordingly, the user may refer to the display unit  15  to check the image displayed by the projector  2 . 
     The control signal input/output unit  16  includes, for example, a local area network (LAN) terminal connectable to a LAN cable, a RS-232C terminal, and a Universal Serial Bus (USB) terminal. A signal for controlling the projector  2  is output from the control signal input/output unit  16  to the projector  2 . 
     As shown in  FIG. 3 , the projector  2 , which projects and displays an image on a plane such as a screen, includes various optical components for projecting and displaying images. For example, the projector  2  includes a plurality of lamps  21 , an optical path switching device  24 , an image generation unit  25 , which generates an image with light, and a projection lens  26 , which enlarges and projects an image. The projector  2  projects and displays an image to present a video content. 
     In the first embodiment, the lamps  21  of the projector  2  include a first lamp  21   a  and a second lamp  21   b . The first lamp  21   a  serves as a first light source for displaying an image, and the second lamp  21   b  serves as a second light source for displaying an image. The first lamp  21   a  and the second lamp  21   b  are each accommodated in a lamp unit  20  and formed by a discharge lamp such as an ultrahigh pressure mercury lamp or a metal halide lamp. 
     As shown in  FIG. 4 , the lamp unit  20  is a light source device including a single lamp  21 , a control unit  22  provided exclusively for the single lamp  21 , and a memory  23  for storing the cumulative activation time or the like of the lamp  21 . The control unit  22  executes data processing based on a control signal received from a main control unit  54  (refer to  FIG. 3 ) of the projector  2 . For example, the control unit  22  stores information, such as the cumulative activation time and operation history of the lamp  21 , in the memory  23  and reads information from the memory  23 . 
     Referring to  FIG. 3 , the optical path switching device  24  switches the light guided to the image generation unit  25  between the light emitted from the lamp  21   a  or the light emitted from the second lamp  21   b . For example, the optical path switching device  24  switches the optical path based on a control signal received from the control unit  54  by driving a reflection mirror connected to an electric motor. The use of such an optical path switching device  24  allows for the image generation unit  25  and the projection lens  26  to be shared by the optical paths formed by the lamps  21 . 
     The image generation unit  25  includes a liquid crystal panel, which is a dot matrix type light valve, and a digital micromirror device (DMD), which has micromirrors arranged in a grating. The image generation unit  25  generates an image with the light emitted from the first lamp  21   a  or the second lamp  21   b  that is passed through the liquid crystal panel and reflected by the DMD. The image generation unit  25  drives the liquid crystal plane and the DMD based on the video signal. 
     The projection lens  26  includes a lens group, which enlarges and projects the light of the image generated by the image generation unit  25 . The projector  2  projects the light of an image with the projection lens  26  to display the image on a screen, a wall, or the like. 
     Further, as shown in  FIG. 3 , the projector  2  includes a power supply unit  31  and a relay  32 . The power supply unit  31  supplies power to the first lamp  21   a  and the second lamp  21   b . The relay  32  switches the destination of the power supplied from the power supply unit  31  between the first and second lamps  21   a  and  21   b.    
     The power supply unit  31  includes a circuit for obtaining power from a commercial power supply in correspondence with each functional unit of the projector  2  and supplies the first lamp  21   a  and the second lamp  21   b  with power via the relay  32 . Based on a control signal received from the main control unit  54  of the projector  2 , the power supply unit  31  controls the lamps  21  so that one is on, or activated, and the other is off, or deactivated. In addition to the first lamp  21   a  and the second lamp  21   b , the power supply unit  31  supplies the control unit  54  of the projector  2 , the control unit  22  of each lamp unit  20 , and the like with power. 
     The relay  32  supplies one of the lamps  21  with the power from the power supply unit  31 . That is, the relay  32  selectively supplies the first lamp  21   a  and the second lamp  21   b  with the power from the power supply unit  31 . The relay  32  switches the destination of the power supply based on the control signal received from the main control unit  54  of the projector  2 . 
     When power is supplied from the power supply unit  31  to the first lamp  21   a , the first lamp  21   a  is on, or activated. In this state, the supply of power to the second lamp  21   b  is stopped. Thus, the second lamp  21   b  is off, or deactivated. In the same manner, when power is supplied from the power supply unit  31  to the second lamp  21   b , the second lamp  21   b  is on, or activated. In this state, the supply of power to the first lamp  21   a  is stopped. Thus, the first lamp  21   a  is off, or deactivated. 
     The projector  2  includes a video signal input unit  41  and a video signal processing unit  42 . The video signal input unit  41  receives a video signal from an external device connected to the projector  2 . The video signal processing unit  42  performs predetermined signal processing on the video signal. 
     The video signal input unit  41  includes, for example, an HDMI terminal and a VGA terminal. In the first embodiment, the computer  1 , which serves as an external device connected to the projector  2 , provides the projector  2  with a video signal via the video signal input unit  41 . 
     The video signal processing unit  42  performs various types of signal processing on a video signal provided to the projector  2 . The video signal is then provided from the video signal processing unit  42  to the image generation unit  25 . 
     The projector  2  further includes an operation unit  51 , a memory  52 , and a control signal input/output unit  53 . The operation unit  51  is operated by the user. The memory  52  stores information such as programs. The control signal input/output unit  53  inputs and outputs control signals to and from the external device connected to the projector  2 . 
     The operation unit  51  includes, for example, buttons or a touch panel pushed by the user. When the operation unit  51  is operated, various types of signals are input to the control unit  54 , and the control unit  54  executes controls in accordance with the operation contents of the operation unit  51 . 
     The memory  52  includes a non-volatile memory (e.g., flash memory) that allows for information to be written and deleted. In addition to programs executed by the control unit  54 , information such as the activation periods of the lamps  21  is stored in the memory  52 . 
     The control signal input/output unit  53  includes, for example, a LAN terminal connectable to a LAN cable, an RS-232C terminal, and a USB terminal. The control signal input/output unit  53  provides the projector  2  with signals output from the computer  1  to control the projector  2 . 
     The control unit  54  is an integrated circuit that outputs control signals or the like to each functional unit of the projector  2 . The control unit  54  is formed, for example, by a microcomputer and executes the programs stored in the memory  52  to control each functional unit of the projector  2 . 
     Based on the information stored in the memory  52  and signals provided from an external device connected to the projector  2 , the control unit  54  controls the optical path switching device  24 , the power supply unit  31 , and the relay  32  to switch the lamps  21 . In other words, the control unit  54  controls the power supplied by the power supply unit  31  and the relay  32  to control the activation and deactivation of the lamps  21 . In the first embodiment, the control unit alternatively switches the activation of the first lamp  21   a  and the activation of the second lamp  21   b.    
     Further, the control unit  54  performs various types of determinations based on the executed program. For example, the control unit  54  determines whether or not to activate a predetermined one of the lamps  21  based on factors like the cumulative activation time of the lamp  21  or operational history such as deactivation of the lamp  21 , which are stored in the memory  23 . 
     The user may set the activation periods of the lamps  21 . The control unit  54  of the projector  2  switches the activated lamp  21  based on the activation periods. When the projector  2  is used for digital signage, the user would be the administrator or the like of the projector  2 . 
     Based on the activation period set by the user, the activation period for each activation of at least one of the lamps  21  is settable, or programmable, by the control unit  54 . In the first embodiment, the two lamps  21   a  and  21   b  are alternately activated. Accordingly, each lamp  21  is repeatedly activated and deactivated and thereby activated for a number of times. Therefore, the control unit  54  of the first embodiment sets the activation period of each of the lamps  21  ( 21   a  and  21   b ) for each activation. The activation period is set in accordance with the reproduction time of the displayed image. 
     The projector  2  according to the first embodiment is operated in three selectable activation modes to activate the lamps  21 . More specifically, the projector  2  includes a manual switching mode that switches the lamp  21  that is activated when operated by the user, an automatic switching mode that switches the lamp  21  that is activated based on the set activation period, and a remote control mode that switches the lamp  21  that is activated based on a signal input from an external device. 
     In the manual switching mode, the lamp  21  that is activated is switched when the user operates the operation unit  51 . In the automatic switching mode, the lamp  21  that is activated is automatically switched based on an activation program, which includes information of the activation period stored in the memory  12 . 
     In the remote control program, the lamp  21  that is activated is switched based on the control of the computer  1 , which serves as an external device connected to the projector  2 . In the first embodiment, when the remote control mode is selected, the activated lamp  21  is switched when the operation unit  14  of the computer  1  is operated. 
     With reference to  FIG. 5 , the processing performed to set an activation program for the automatic switching mode will now be discussed. The control unit  54  starts the series of processes shown in  FIG. 5  when, for example, receiving a setting start signal for the activation program from the operation unit  51 . The activation program need only be set before the lamps  21  are actually activated in the automatic switching mode. Accordingly, the activation program may be set in advance before the automatic switching mode is selected or immediately after the automatic switching mode is selected. 
     As shown in  FIG. 5 , the control unit  54  first obtains information of the lamp  21  that is to be activated (step S 1 ). For example, the control unit  54  obtains information of the one of the lamps  21  that is to be activated based on the selection performed with the operation unit  51  by the user. In the first embodiment, either one of the first lamp  21   a  and the second lamp  21   b  is selected. 
     Then, the control unit  54  obtains information for the length of time, or period, of a single activation of the selected lamp  21  (step S 2 ). For example, the control unit  54  obtains the activation period information based on the selection performed with the operation unit  51  by the user. 
     Next, the control unit stores in the memory  52  the information of the lamp  21  obtained in step S 1  in association with the information of the activation period obtained in step S 2  (step S 3 ). This sets the period for a single activation of the single lamp  21 . 
     Finally, the control unit  54  determines whether or not to complete the setting of the activation program (step S 4 ). For example, the control unit  54  determines whether or not an operation for completing the setting of the activation program has been performed with the operation unit  51  and completes the setting of the activation program when receiving a setting completion signal from the operation unit  51 . 
     When the setting of the activation program is not completed, the control unit  54  repeats steps S 1  to S 3 . By repeating steps S 1  to S 3 , the lamp  21  that is to be activated and the activation period for each activation of the lamp  21  are set so as to generate a program list such as that shown in  FIG. 6 . 
     The program list shown in  FIG. 6  is one example of an activation pattern of the lamps  21  including the set contents of the activation program and stored in the memory  52 . In  FIG. 6 , “n” represents a natural number and is either “1” or “2” in the first embodiment. In  FIG. 6 , “K” represents a natural number corresponding to the time length of the displayed image. 
     In the first embodiment, the information for the lamp  21  that is to be activated and the information for the activation period are associated with a list number. The list number is a distinguishable code and indicates an activation order of the lamps  21 . For example, the program list shown in  FIG. 6  shows a pattern for activating the lamps  21  in the order of “activate the first lamp  21   a  for thirty minutes”, “activate the second lamp  21   b  for one hundred minutes”, “activate the first lamp  21   a  for forty minutes”, and “activate the second lamp  21   b  for twenty minutes”. In other words, the activation periods shown in  FIG. 6  indicates the time intervals in which the activated lamps  21  are switched. Accordingly, in the first embodiment, the time intervals for switching the lamps  21  are set by the activation periods of the lamps  21 . 
     The various information of the program list generated with the operation unit  51  as described above is stored in the memory  52 . 
     In the first embodiment, at least part of the activation pattern of the lamps  21  (i.e., the program list) may be set as a repeat pattern. When a repeat pattern is set, the control unit  54  switches the activated lamps  21  by repeating the repeat pattern. 
     With reference to  FIG. 7 , the processing performed to set the repeat pattern will now be discussed. The control unit  54  starts the series of processes shown in  FIG. 7  when, for example, receiving a setting start signal for the repeat pattern from the operation unit  51 . 
     As shown in  FIG. 7 , the control unit  54  obtains information of whether or not to repeat a predetermined activation pattern as a repeat pattern based on the activation pattern, which has been set as described above (step S 11 ). For example, the control unit  54  obtains information of whether or not to validate execution of the repeat pattern based on the selection performed with the operation unit  51  by the user. 
     Then, the control unit  54  obtains information of a starting point of the repeat pattern (step S 12 ). For example, based on the selection performed with the operation unit  51  by the user, the control unit  54  obtains one of the list numbers in the program list shown in  FIG. 6  as the starting point of the repeat pattern. 
     Next, the control unit  54  obtains information of an ending point of the repeat pattern (step S 13 ). For example, based on the selection performed with the operation unit  51  by the user, the control unit  54  obtains one of the list numbers in the program list shown in  FIG. 6  as the ending point of the repeat pattern. The list number selected as the ending point is a list number of which activation order comes after the list number selected in step S 12 . 
     Then, the control unit  54  obtains information for the number of times to repeat—the repeat pattern (step S 14 ). For example, based on the selection performed with the operation unit  51  by the user, the control unit  54  obtains the number of times to repeat the activation pattern from the starting point of the repeat pattern to the ending point of the repeat pattern. 
     Further, the control unit  54  associates and stores in the memory  52  information for whether or not to repeat the repeat pattern, information for the starting point and ending point of the repeat pattern, and information for the number of repetitions (step S 15 ). As a result, as shown in the example of  FIG. 8 , a repeat list is generated including the information for the repeat pattern (starting point and ending point), the information for whether or not to validate execution of the repeat pattern (ON/OFF), and the information for the number of repetitions. 
     The repeat list shown in the example of  FIG. 8  is stored in the memory  52  in step S 15 . Under the item labeled as “repeat process” in  FIG. 8 , “ON” indicates that execution of the repeated pattern is validated. Accordingly, the repeat list of  FIG. 8  indicates that the activation pattern of list numbers  3  to  4  in the program list of  FIG. 6  is to be repeated six times. More specifically, based on the program list of  FIG. 6  and the repeat list of  FIG. 8 , the control unit  54  executes a program pattern of “activate the first lamp  21   a  for thirty minutes” and “activate the second lamp  21   b  for one hundred minutes”. Then, the control unit  54  repeats for six times a program pattern of “activate the first lamp  21   a  for forty minutes” and activate the second lamp  21   b  for twenty minutes”. 
     The storage of the repeat list in the memory  52  completes the setting of the repeat pattern. In step S 11 , when validation of the execution of the repeat pattern is not selected, the setting of the repeat pattern may be cancelled without performing the operations of steps S 12  to S 14 . 
     The flow of an activation switching control for the lamps  21  will now be discussed with reference to  FIG. 9 . The control unit  54  starts the series of processes shown in  FIG. 9  when, for example, the automatic switching mode is selected with the operation unit  51 . 
     As shown in  FIG. 9 , the control unit  54  first refers to the repeat list and determines whether or not execution of the repeat pattern has been validated (step S 21 ). When the repeat list is not generated, the control unit  54  determines that there is no repeat pattern (step S 21 : NO). 
     When execution of the repeat pattern is validated, the control unit  54  determines whether or not the present list number, which is in accordance with the program list of, for example, that shown in  FIG. 6 , is the starting point of the repeat pattern set in the repeat list of, for example, that shown in  FIG. 8  (step S 22 ). 
     When the present list number is the starting point of the repeat pattern, the control unit  54  performs the repeat process shown in  FIG. 10  (step S 30 ) based on the set repeat list. 
     When execution of the repeat pattern is not validated (step S 21 : NO), the control unit  54  executes the activation program for the present list number in accordance with the program list (step S 23 ). Further, when the present list number is not the starting point of the repeat pattern (step S 22 : NO), the repeat process is suspended, and the control unit  54  executes the activation program for the present list number. In this manner, in step S 23 , the control unit  54  activates the predetermined one of the lamps  21  (the first lamp  21   a  or the second lamp  21   b ) designated by the activation program. 
     Next, the control unit  54  determines whether or not the continuous activation period of the lamp  21  ( 21   a  or  21   b ) that started activation has elapsed a set activation period (step S 24 ). For example, the control unit  54  uses a timer (not shown) to measure the elapsed time from when activation of the lamp  21  started to determine whether or not the measured elapsed time has reached a set activation period. 
     When the set activation period has elapsed, the control unit  54  deactivates the lamp  21  that started activation in step S 23  (step S 25 ). For example, the first lamp  21   a  corresponding to list number  1  in  FIG. 6  is turned off after thirty minutes elapses from when activation started. Further, the second lamp  21   b  corresponding to list number  2  in  FIG. 6  is turned off after one hundred minutes elapses from when activation started. Accordingly, the lamp  21  that starts activation in step S 23  remains activated until the set activation period elapses. 
     Then, the control unit  54  refers to the program list and determines whether or not the lamp  21  that is activated next is set (step S 26 ). 
     When the lamp  21  that is to be activated next is set, the control unit  54  repeats the operations from step S 21 . As a result, based on the activation periods set in the program list, the lamps  21  that are activated are sequentially switched so as to conform to the set activation pattern. 
     With reference to  FIG. 10 , the flow of the repeat process of step S 30  will now be discussed. First, the control unit  54  activates the predetermined lamp  21  ( 21   a  or  21   b ) in accordance with the repeat pattern set in the repeat list (step S 31 ). For example, in the case of the repeat list shown in  FIG. 8 , the control unit  54  activates the first lamp  21   a , which corresponds to list number  3 , which is set as the starting point. 
     Then, in the same manner as in step S 24 , the control unit  54  determines whether or not the continuous activation period of the lamp  21  that started activation has reached a set activation period (step S 32 ). 
     When the set activation period has elapsed, the control unit  54  deactivates the lamp  21  that started activation in step S 31  (step S 33 ). 
     Then, the control unit  54  determines whether or not the list number of the activation program of which execution has presently been completed is an ending point of the repeat pattern (step S 34 ). For example, in the case of the repeat list shown in  FIG. 8 , the control unit  54  determines whether or not the activation program of which execution has presently been completed is the activation program corresponding to list number  4 . 
     When the list number is not the ending point of the repeat pattern (step S 34 : NO), the control unit  54  repeats steps S 31  to  533 . By repeating steps S 31  to  533 , the activated lamps  21  are switched in accordance with the repeat pattern from the starting point to the ending point. 
     When the list number is the ending point of the repeat pattern (step S 34 : YES), the control unit  54  determines whether or not the repeat pattern has been repeated for the set number of times to repeat (step S 35 ). 
     When the repeat pattern has not be repeated for the set number of times to repeat (step S 35 : NO), the operations of steps S 31  to S 34  are repeated. As a result, the repeat pattern from the starting point to the ending point is repeated for the set number of times to repeat. 
     When the repeat pattern has been repeated for the set number of times to repeat (step S 34 : YES), the repeat process ends and the processing proceeds to step S 26  of  FIG. 9 . 
     When the lamp  21  that is to be activated reaches the end of its life or when the lamp  21  becomes defective, the switching of the lamps  21  is performed in a manner irrelevant to the set activation program even if the automatic switching mode is selected. In other words, when the automatic switching mode is selected and the control unit  54  determines that the predetermined lamp  21  cannot be activated to display an image, the switching control of the lamps  21  based on the set activation program is prohibited. 
     The image display system of the first embodiment has the advantages described below. 
     (1) The activation period of each lamp  21  is set for each activation. That is, the control unit  54  is capable of setting the activation period for each activation of the repetitively activated first lamp  21   a  or second lamp  21   b . This increases the freedom for setting the activation period of each lamp  21  and allows for the activation pattern of each lamp  21  to be flexibly set. Accordingly, the activation pattern of the lamps  21  is not fixed and is variable in accordance with the various video contents presented with the projector  2 . This enables the closing of a video content to be synchronized with the switching of the activated lamps  21  so that the presentation of the video contents is not interrupted when switching the activation of the lamps  21 . 
     (2) The activation period is settable for each activation of each lamp  21  (i.e., the first lamp  21   a  and the second lamp  21   b ) in the projector  2 . This allows for flexible setting of an activation pattern that combines all of the lamps  21 . 
     (3) The user may freely set the activation period of each lamp  21  by operating the operation unit  51  of the projector  2 . 
     (4) The control unit  54  programs the activation pattern of the lamps  21  based on the activation periods set by the user with the operation unit  51 . This allows for the activation pattern of the lamps  21  to be set with further flexibility. That is, the programmed activation pattern of the lamps  21  may be one that activates the lamps  21  in an order that is desirable for the user. 
     (5) The control unit  54  executes a control for switching and activating the lamps  21  based on the information stored in the memory  52  (i.e., the activation periods set in the program list). Accordingly, the external device (computer  1 ), which is connected to the projector  2 , does not have to be used to control the switching timing of the lamps  21 . 
     (6) The control unit  54  sets whether or not to use at least part of the activation pattern in the program list as a repeat pattern. When using the repeat pattern, the control unit  54  repeats part of the program list in accordance with the repeat pattern. This allows for elimination of the burden for setting the activation period of each lamp  21  for each activation. 
     (7) The control unit  54  repeats the repeat pattern for the number of times set in the repeat list. Thus, a predetermined activation pattern included in the program list may be repeated for the number of times desired by a user. 
     (8) The control unit  54  is capable of selectively executing the automatic switching mode, which switches the lamps  21  based on preset activation periods, and the manual switching mode, which switches the lamps  21  based on a user operation. Thus, the user may select the desirable activation mode in accordance with the application of the projector  2 . 
     (9) The control unit  54  is capable of further selecting the remote control mode, which switches the lamps  21  based on signals provided from the computer  1 . Accordingly, when the image display system includes a plurality of projectors  2 , the use of the remote control mode eliminates the need for setting the activation pattern for each projector  2  and facilitates the control of the plurality of projectors  2 . 
     Second Embodiment 
     An image display system according to a second embodiment will now be discussed with reference to  FIGS. 11 to 18 . The image display system of the second embodiment includes a computer  1  (controller), which has a structure similar to that of the first embodiment shown in  FIG. 2 , and a plurality of projectors  2  (video projectors  2 ), each having a structure similar to that of the first embodiment shown in  FIGS. 3 and 4 . To avoid redundancy, like or same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described. 
     As shown in  FIG. 11 , the image display system further includes an image reproduction device  6 , which serves as a video signal output device that outputs video signals to the projectors  2 . 
     In the second embodiment, the memory  12  of the computer  1  further stores information for controlling the image reproduction device  6 . The image reproduction device  6  is controlled by signals from the control signal input/output unit  16  of the computer  1 . The computer  1  retrieves information related to the lamps  21  and information related to video contents through the control signal input/output unit  16  and stores the retrieved information in the memory  12  of the computer  1 . 
     In the second embodiment, the image reproduction device  6 , which is an external device, provides each projector  2  with a video signal via the video signal input unit  41  of each projector  2 . Each projector  2  provides the computer  1  with signals representing information related to the lamps  21  via the control signal input/output unit  53 . The information related to the lamps  21  includes, for example, the quantity of the lamps  21  in each projector  2  and lamp IDs for distinguishing each lamp  21 . 
     As shown in  FIG. 12 , the image reproduction device  6  includes a storage device  61 , a video signal output unit  62 , a control unit  63 , and a control signal input/output unit  64 . The storage device  61  reads video information stored in an electronic storage medium (not shown). The video signal output unit  62  outputs the video information read by the storage device  61  as a video signal. The control unit  63  controls each functional unit in the image reproduction device  6 . The control signal input/output unit  64  receives control signals from the computer  1 , which is an external device. 
     The storage device  61  is, for example, an optical drive that reads image information from an optical disk such as a DVD serving as an electronic storage medium. The video signal output unit  62  includes an HDMI terminal or VGA terminal for outputting video signals to each projector  2  connected to the image reproduction device  6 . The electronic storage medium stores information for images corresponding to various types of video contents. The storage device  61  reads video information from the electronic storage medium and outputs the video information as a video signal to each projector  2  via the video signal output unit  62  based on a control signal provided from the control unit  63 . 
     The control unit  63  is an integrated circuit for outputting a control signal to each functional unit of the image reproduction device  6 . The control unit  63  is formed by, for example, a microcomputer and provides the storage device  61  with a control signal for outputting the video signal to each projector  2  based on a control signal provided from the computer  1 . 
     The control signal input/output unit  64  includes, for example, a LAN terminal connectable to a LAN cable, an RS-232C terminal, and a USB terminal. The control signal input/output unit  64  provides the image reproduction device  6  with a control signal from the computer  1 . The control signal includes, for example, a signal for outputting a predetermined video signal from the image reproduction device  6 . Further, the image reproduction device  6  provides the computer  1  with information related to a video content via the control signal input/output unit  64 . Information related to a video content includes, for example, a video reproduction time, which is the presentation time of a video content, and a video content ID, which is for distinguishing each of a plurality of video contents. 
     Accordingly, in the second embodiment, the image reproduction device  6  provides the projectors  2  with video signals. That is, the control signal provided from the computer  1  controls the projectors  2  and the image reproduction device  6 . 
     In the second embodiment, the activation period of each lamp  21 , which is activated for a number of times, is set for each activation. The activation period is set in accordance with the reproduction time of the displayed image by, for example, operating the operation unit  14  of the computer  1 . 
     In the second embodiment, the projectors  2  are operated in any one of three selectable activation modes, that is, the manual switching mode, the automatic switching mode, and the remote control mode. In particular, the remote control mode will now be discussed. When the remote control mode is selected, the control unit  11  of the computer  1  executes a control program including an activation program stored in the memory  12  to automatically switch the activated lamps  21 . 
     The flow of the control program related to the remote control mode will now be discussed with reference to  FIG. 13 . The control unit  11  of the computer  1  starts the series of processes shown in  FIG. 13  when receiving a setting start signal for the activation program from the operation unit  14 . The control program need only be set before actually controlling the activation of the lamps  21  in the remote control mode. 
     As shown in  FIG. 13 , the control unit  11  first obtains control timing information indicating the starting time or changing time for the control operation of the projectors  2  and the image reproduction device (step S 41 ). For example, the control unit  11  obtains the time designated by a user with the operation unit  14  as control timing. Alternatively, as will be described later, the control timing may be automatically set based on previous control contents. 
     Then, the control unit  11  obtains the information of the control contents of the projector  2  and the image reproduction device  6  (step S 42 ). For example, the control unit  11  selects the control contents designated by a user with the operation unit  14 . Alternatively, as will be described later, the control timing may be automatically set based on the previous control contents. In the second embodiment, in step S 42 , one of “start reproduction”, “end reproduction”, and “switch lamps” is selected as the control content. The phrase “start reproduction” refers to a control that starts the output of a video signal from the image reproduction device  6  and activates the lamps  21  of the projectors  2 . The phrase “end reproduction” refers to a control that stops the output of a video signal from the image reproduction device  6 . The phrase “switch lamps” refers to a control for deactivating an activated lamp  21  to switch activated lamps  21 . 
     Next, the control unit  11  determines whether or not the control content is “start reproduction” (step S 43 ). 
     When the control content is “start reproduction”, the control unit  11  obtains information of the video content that is to be presented (step S 44 ). For example, the control unit  11  selects a video content designated by a user with the operation unit  14 . 
     Then, the control unit  11  obtains information of the lamp  21  that is to be activated (step S 45 ). For example, the control unit  11  selects the lamp  21  designated by the user with the operation unit  14 . The selected lamp  21  is activated at the starting time, which has been set as the control timing. In the same manner as in the first embodiment, in each projector  2 , the lamps  21  include a first lamp  21   a  and a second lamp  21   b . Accordingly, the control unit  11  selects either one of the first lamp  21   a  and the second lamp  21   b.    
     Next, the control unit  11  obtains information of whether or not to repeat reproduction of the image (contents) selected in step S 44  (step S 46 ). The repeat reproduction information may be set with, for example, the operation unit  14 . If a repeat reproduction function is valid, when the presentation of a video content ends within the activation period of the lamp  21  (i.e., when the reproduction of an image ends), the presentation of the video content is repeated. 
     Then, based on the information obtained in step S 46 , the control unit  11  determines whether or not to repeat reproduction of the image (step S 461 ). 
     When repeating reproduction (step S 461 : YES), the control unit  11  obtains information of the number of times for repeating reproduction (step S 462 ). The number of times to repeat may be set, for example, with the operation unit  14 . When reproduction is not repeated (step S 461 : NO), step S 462  is not performed. 
     When the number of times to repeat is set in step S 462 , the control program may be set so as to repeat the control of “start reproduction” and “end reproduction” for the number of times set for repetition. When “end reproduction” is selected as the control content, the time for ending the presentation of a video content (i.e., the control timing of “end reproduction”) may be automatically set by adding the presentation time length of the video content to the time for starting the presentation of the video content (i.e., the control timing of “start reproduction”). Moreover, a time immediately after the ending time may be automatically set as a starting time for the presentation of a video content, and a further ending time for the presentation of the video content may be set by adding the presentation time length of the video content to the starting time. 
     Then, the control unit  11  associates and stores the information obtained in at least steps S 41  and S 42  (step S 47 ). In this state, when “start reproduction” is selected as the control content in step S 42 , the control unit  11  associates the information obtained in steps S 41 , S 42 , and S 44  to S 46 . That is, the control unit  11  associates and stores in the memory  12  information of the control timing, information of the control contents, information of the video contents that are to be presented, information of the lamp  21  that is to be activated, and information of whether or not to repeat reproduction. In this manner, the operation unit  14  is operated to store in the memory  12  the information of the control timing for “start reproduction” and the information of the lamp  21  that is to be activated. This sets the lamp  21  that is to be activated and the timing for activating the lamp  21 . 
     Further, in step S 47 , information of the video content that is to be presented is stored in the memory  12  to set the image displayed by the projectors  2 . Further, in step S 47 , the memory  12  stores in the memory  12  information of whether or not to repeat reproduction. This sets whether or not to repeat presentation of the video content. 
     When the control content is not “start reproduction” in step S 43 , that is, when “end reproduction” or “switch lamps” is selected in step S 42 , the control unit  11  proceeds to step S 47  to associate and store in the memory  12  the information of the control timing obtained in step S 41  and the information of the control content obtained in step S 42 . 
     Steps S 41  to S 47  are repeated. In this case, when “start reproduction” is selected in step S 42 , “end reproduction” may be automatically selected the next time S 42  is performed. Further, in step S 47 , the information of the control timing of “start reproduction” and “end reproduction” may be stored in the memory  12 . Accordingly, by repeating steps S 41  to S 47 , the activation period is set for each activation of each lamp  21 , which is activated a number of times. 
     When step S 42  is performed the first time, “start reproduction” may be automatically set. Further, when “end reproduction” is selected in step S 42 , “end reproduction” may be selected the next time step S 42  is performed. When “switch lamps” is selected in step S 42 , “start reproduction” may be automatically selected the next time step S 42  is selected. 
     After “end reproduction” is selected in step S 42 , when “start reproduction” is selected the next time step S 42  is performed, the control for switching the lamps  21  is not executed. Thus, step S 45  does not have to be performed. 
     When “end reproduction” is selected in step S 42 , it is preferable that the control timing corresponding to the ending time for the presentation of a video content be automatically set in accordance with the presentation time of the video content (i.e., reproduction time of image) obtained from the video content information. 
     Finally, the control unit  11  determines whether or not to complete the setting of the control program (step S 48 ). For example, the control unit  11  determines whether or not an operation for completing the setting of the control program has been performed with the operation unit and completes the setting of the control program when receiving a setting completion signal from the operation unit  14 . 
     The control unit  11  repeats steps S 41  to S 47  when not completing the setting of the control program. The repetition of steps S 41  to S 47  sets the lamp  21  that is to be activated and the activation period for each activation of the lamp  21  and generates, for example, a program list as shown in  FIG. 14 . 
     The program list of  FIG. 14  is stored in the memory  12  and shows one example of an activation pattern of the lamps indicating the setting contents of an activation program. 
     In the second embodiment, the information of the control timing, the information of the control contents, the information of the video contents, the information of the lamp  21  that is to be activated, and the information of whether or not to repeat reproduction are associated with a list number. The list number is a distinguishable code and indicates an activation order of the lamps  21 . For example, the program list shown in  FIG. 14  shows an activation pattern of the activated lamp  21  in the order of “activate the first lamp  21   a  for approximately thirty minutes”, “activate the second lamp  21   b  for approximately one hundred minutes”, and “activate the first lamp  21   a  for approximately forty minutes”. 
     Further, under the item labeled as “repeat reproduction” in  FIG. 14 , “ON” indicates that reproduction is repeated, and “OFF” indicates that reproduction is not repeated. For example, list numbers  1  to  2  in the program list of  FIG. 14  indicates that reproduction of the image of content A is repeated for approximately thirty minutes during which the first lamp  21   a  is activated. 
     Under the item labeled as “video contents” in  FIG. 14 , “contents A”, “contents B”, “contents C”, and “contents D” represent commercial purpose video contents as the video contents that are to be presented. Under the same item labeled as “video contents”, “switch period image” represents non-commercial purpose video contents that are not used for advertisement of products and services or for the introduction of a facility. 
     In the second embodiment, when “switch lamps” is selected in step S 42 , “switch period image” is automatically selected as the video content the next time step S 44  is performed. That is, referring to  FIG. 14 , for approximately twenty seconds from when activation starts with the lamp  21 , which has been switched based on the “switch lamps” control, to when the illuminance of the lamp  21  stabilizes, selection of commercial purpose video contents (i.e., contents A to D) as the video content that is to be presented is prohibited. When an image is reproduced from immediately after activation of the lamp  21  starts, an image displayed when the illuminance is still insufficient is difficult to view. This may result in a disadvantage such as information not being conveyed to the audience. To cope with this problem, in the second embodiment, during the period from when activation starts to when the illuminance of the lamp  21  stabilizes, a non-commercial purpose is displayed. When the illuminance of the lamp  21  stabilizes, a commercial purpose image is shown. 
     The presentation time of the “switch period image”, that is, the reproduction time of the image displayed until the illuminance of the lamp  21  stabilizes may be changed by the user. Such a structure would satisfy a demand for setting a longer presentation time for the “switch period image” to ensure that commercial purpose video contents are presented in a state in which the illuminance is stabilized or ensure a demand for quickly presenting a video content other than the “switch period image”. 
     Further, the illuminance of the lamp  21  may be measured with a sensor, and presentation of a “switch period image” may be completed when the measured illuminance becomes greater than or equal to a fixed value. When the illuminance becomes greater than or equal to the fixed value, such a structure would ensure completion of the “switch period image” and allow for the presentation of a further video content. That is, an illuminance that is greater than or equal to the fixed value would be guaranteed when presenting the video contents of contents A to D, and the presentation of video content to the audience would be further ensured. 
     The various types of information in the program list generated with the operation unit  14  are stored in the memory  12 . 
     The computer  1  provides the projectors  2  with the information of the activation program generated in the setting process ( FIG. 13 ) of the control program. More specifically, based on the information stored in the memory  12  of the control timing and the lamp  21  that is to be activated, the computer  1  outputs from the control signal input/output unit  16  information of the time for switching the lamps  21  and information of the lamp  21  subject to switching. The information output as the control signal from the control signal input/output unit  16  is input to the control signal input/output unit  53  of each projector  2 . Accordingly, the control signal input/output unit  53  is provided with a signal indicating the switching time of the lamps  21  as a signal indicating the activation period. This stores the activation program, which includes information of the activation period, in the memory  52  of each projector  2  and completes the setting of the activation program for the projector  2 . 
     The flow of the process for storing the activation program in the memory of each projector  2  will now be discussed with reference to  FIG. 15 . The control unit  54  of the projector  2  starts the series of processes shown in  FIG. 15  when, for example, receiving a signal for selecting the remote control mode from the computer  1 . The storage of the activation program in the memory  52  is performed before the control process of the lamps  21  in the remote control mode. 
     As shown in  FIG. 15 , the control unit  54  of the projector  2  first obtains information of the time for switching the activated lamp  21  from the computer  1  via the control signal input/output unit  53  (step S 51 ). Based on the information of the switching time, the control unit recognizes the timing for deactivating the activated lamp  21  and the timing for activating the deactivated lamp  21 . 
     Next, the control unit  54  obtains information of the lamp  21  of which activation state is subject to switching from the computer  1  via the control signal input/output unit  53  (step S 52 ). This obtains at least either one of information of the lamp  21  that is to be activated at a predetermined timing and information of the lamp  21  that is to be deactivated at a predetermined timing. 
     Further, the projector  2  associates and stores in the memory  52  the information of the switching time obtained in step S 51  and the information of the lamp  21  subject to switching obtained in step S 52  (step S 53 ). As a result, a program list such as that shown in  FIG. 16  is generated. 
     The program list shown in  FIG. 16  is one example of an activation pattern of the lamp  21  showing the setting contents of the activation program and is stored in the memory  52  in step S 53 . In  FIG. 16 , “h” represents a natural number. Further, “m” and “s” represents an integer of 0 to 59. Additionally, in  FIG. 16 , “n” represents either “1” or “2” in the second embodiment. 
     The activation program shown in  FIG. 16  has the same contents as the activation program included in the control program of  FIG. 14  represents an activation pattern in which the activation of the lamps  21  is switched in the order of “activate the first lamp  21   a  for thirty minutes” and “activate the second lamp  21   b  for one hour forty minutes and twenty seconds”. In this manner, the time for switching the lamps  21  may be represented as the activation period for a single activation of the lamp  21 , and the activation period of the lamp  21  is set by setting the time for switching the lamp  21 . 
     The time for switching the lamps  21  and the activation periods of the lamps  21  are set based on a signal output from the computer  1  to the projectors  2 . Accordingly, based on a control timing set by the user, the computer  1  controls the projectors  2  that the activated lamps  21  and activation periods are as set by the user. When controlling the activation of the lamps  21 , the computer  1  also controls the image reproduction device  6  so as to display the image set by the user during the activation period, which is set by the user. Based on the control program and activation program, which are set as described above, a control for inputting to the projector  2  a video signal corresponding to the video content that is to be presented and a control for sequentially activating the lamps  21  are executed. 
     To output a video signal corresponding to a video content that is to be presented, the computer  1  provides the image reproduction device  6  with a control signal of “start reproduction” or “end reproduction” at the set control timing. The control signal of “start reproduction” is a signal for outputting a predetermined video signal from the image reproduction device  6 . The control signal of “end reproduction” is a signal for stopping the output of a predetermined video signal from the image reproduction device  6 . 
     The flow of a process for providing a video signal corresponding to the video content that is to be presented from the image reproduction device  6  to each projector  2  will now be discussed with reference to  FIG. 17 . The control unit  63  of the image reproduction device  6  starts the series of processes shown in  FIG. 17  when receiving from the computer  1  the control signal of “start reproduction” at a control timing set in the remote control mode. For example, in the control program shown in  FIG. 14 , when starting control in the remote control mode, the control unit  63  starts the series of processes shown in  FIG. 17  at control timings such as thirty minutes and five seconds, thirty minutes and twenty seconds, and one hour ten minutes and twenty seconds. 
     As shown in  FIG. 17 , the control unit  63  first starts the output of the video signal corresponding to the video content that is to be presented (step S 61 ). For example, in the case of the control program shown in  FIG. 14 , when starting the control process of “start reproduction” registered in list number  1 , the control unit  63  receives a control signal for presenting content A from the computer  1  via the control signal input/output unit  64 . Based on the control signal, the control unit  63  reads video information corresponding to content A and outputs the video information as a video signal from the video signal output unit  62 . Contents A to D are commercial purpose contents, and images corresponding to contents A to D are for advertisement of a product or service or for introduction of a facility. 
     Then, the control unit  63  determines whether or not a control signal of “end reproduction” has been received from the computer  1  via the control signal input/output unit  64  (step S 62 ). 
     When the control signal of “end reproduction” is not received, the control unit  63  determines whether or not image reproduction has been completed (step S 63 ). When image reproduction has not been completed, step S 62  is repeated. Further, the control unit  63  continues the output of the input signal corresponding to a video content until the control signal of “end reproduction” is received or until image reproduction is completed. 
     Further, when image reproduction is completed without receiving the control signal of “end reproduction”, the control unit  63  determines whether or not to repeat reproduction of the image (step S 64 ). This determination is made based on a control signal representing repeat reproduction information and provided from the computer  1 . That is, the control unit  63  determines whether the repeat reproduction information represents valid or invalid. 
     When image reproduction is not repeated, the processing returns to step S 62 . Accordingly, the control unit  63  maintains the state in which the video signal corresponding to a video content is output until receiving the control signal of “end reproduction”. 
     When repeating image reproduction, the control unit  63  determines whether or not the video content has been repeated for a predetermined number of times (step S 641 ). The determination is made based on a control signal representing information indicating the number of repetitions and provided from the computer  1 . 
     When the image has not been repeated for the number of times for repetition (step S 62 : NO), the processing returns to step S 61 . Accordingly, the output of a video signal corresponding to the video contents that is to be presented is restarted, and presentation of the video content is repeated until the required number of repetitions has been met. Further, the control unit  63  continues to output the video signal corresponding to the video content until receiving the control signal of “end reproduction”. In this manner, when repeating presentation of the video content, during the activation period of the lamp  21  that is synchronous with the control timings for “start reproduction” and “end reproduction”, the set image is repeatedly reproduced and displayed. 
     When receiving the control signal of “end reproduction” (step S 62 : YES), the control unit  63  stops outputting the video signal (step S 65 ). In this manner, the control unit  63  controls the output of the video signal with the control signal from the computer  1 . In other words, the computer  1  controls the image reproduction device  6  so as to output the video signal corresponding to the set image. 
     By repeating the series of processes described above, the image reproduction device  6  sequentially provides the projector  2  with video signals corresponding to various video contents. In the second embodiment, the image reproduction device  6  is connected to the plurality of projectors  2 . Thus, the projectors  2  are provided with the same video signal. 
     The flow of the operation of the projector  2  when sequentially activating the lamps  21  in the remote control mode will now be discussed with reference to  FIG. 18 . The series of processes shown in  FIG. 18  start when the computer  1  provides the control unit  54  of each projector  2  with a signal for selecting the remote control mode, and the activation program (program list) of the lamps  21  is stored in the memory  52 . 
     As shown in  FIG. 18 , the control unit  54  of the projector  2  activates the lamps  21  in accordance with the set activation pattern (step S 71 ). For example, when the program list shown in  FIG. 16  is stored in the memory  52 , the control unit  54  first activates the first lamp  21   a  (for details, refer to  FIG. 14 ). In this case, the control unit  54  continues to activate the first lamp  21   a  for thirty minutes and activates the second lamp  21   b  after thirty minutes elapses. In this manner, in step S 71 , based on the program list stored in the memory  52 , the control unit  54  activates the first lamp  21   a  or the second lamp  21   b.    
     Next, the control unit  54  determines whether the time for switching the activated lamp  21  has arrived (step S 72 ). For example, the control unit  54  measures the elapsed time from when activation of the lamp  21  starts with a timer (not shown) and determines whether or not the measured elapsed time has reached a switching time for the lamp  21  stored in the memory  52 . 
     When the switching time has not been reached, the process of step S 72  is continued. When the switching time has been reached, the control unit  54  deactivates the lamp  21  that started activation in step S 71  (step S 73 ). For example, when the program list shown in  FIG. 16  is stored in the memory  52  and the activation period of the first lamp  21   a  that first started activation reaches thirty minutes, the first lamp  21   a  is deactivated. Further, as the activation period of the second lamp  21   b  that started activation when thirty minutes elapsed reaches two hours ten minutes and twenty seconds, the second lamp  21   b  is deactivated. In this manner, in step S 73 , the control unit  54  activates the first lamp  21   a  or the second lamp  21   b  based on the program list stored in the memory  52 . In other words, the lamp  21  that starts activation in step S 71  continues activation until the next switching time is reached. 
     The timing in which the projector  2  activates the lamp  21  in step S 71  and the timing in which the image reproduction device  6  starts the output of the video signal are synchronized with when the control process of the lamps  21  is started in the remote control mode. Accordingly, the computer  1  controls the projectors  2  and the image reproduction device  6  so as to switch and activate the lamps  21 , which are activated in accordance with the displayed image. 
     Finally, the control unit  54  of the projector  2  determines whether or not the lamp  21  that is to be activated next is set in the program list (step S 74 ). 
     When the lamp  21  that is to be activated next is set, steps S 71  to S 73  are repeated. This switches the activated lamps  21  at the switching time set in the program list. 
     In addition to advantages (1), (2), (5), (8), and (9) of the first embodiment, the image display system of the second embodiment has the advantages described below. 
     (10) The projectors  2  receive a signal indicating the activation period from the computer  1  to set the activation period of each lamp  21 . This allows for the activation period of each lamp  21  in the projectors  2  to be remote controlled from the computer  1 . 
     (11) When starting activation of a lamp  21 , each projector  2  displays a predetermined image until the illuminance of the lamp  21  stabilizes. After the illuminance of the lamps  21  stabilizes, the displayed image is switched. For example, an image of which purpose is not for advertisement of products and services or for introduction of a facility is displayed until the illuminance of the lamp  21  that started activation stabilizes. After the illuminance of the lamp  21  stabilizes, an image of which purpose is for advertisement of products and services or for introduction of a facility is displayed. Thus, in a state in which the illuminance of the lamp  21  is not stable, commercial purpose video contents are not presented. 
     (12) The computer  1  controls each projector  2  so as to switch and activate the lamps  21  in accordance with the displayed image. Thus, the activated lamps  21  are switched in accordance with an activation pattern corresponding to the various video contents presented by the projectors  2 . This synchronizes the closing of a video content and the switching of the lamps  21 . Thus, the switching of the lamps  21  does not interrupt the presentation of the video content. 
     (13) The computer  1  sets the activation period of each lamp  21  for each activation based on the contents set by the user with the operation unit  14 . Further, the computer  1  provides the projectors  2  with a signal indicating activation periods to control the switching of the lamps  21  in the projectors  2 . This allows for the switching of the lamps  21  in the projectors  2  to be remote controlled from the computer  1 . 
     (14) Based on the contents set by the user with the operation unit  14 , the computer  1  sets the activation pattern of the lamps  21  in the projectors  2  in an activation order and activation period desirable to the user. 
     (15) Based on the contents set by the user with the operation unit  14 , the computer  1  sets the timing for activating the lamps  21  and switches the lamps  21  at the set timings. This generates an activation pattern that switches the activation of the lamps  21  at timings desirable to the user. 
     (16) The projectors  2  may display images designated by the user in the set activation period. 
     (17) The computer  1  controls the image reproduction device  6  so as to output a video signal corresponding to the set image during the set activation period. This allows for the plurality of projectors  2  to display the same image by outputting a video signal to the projectors  2  from the image reproduction device  6 . 
     (18) Repeated presentation of a video content is set. When repeating presentation of a video content, reproduction of the set image is repeated during the set activation period. Thus, even when the reproduction of an image ends in the set activation period, the video image may be presented again. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     In the first embodiment, instead of the time intervals for switching the lamps  21 , activation periods of the lamps  21  may be set by timings for switching of the lamps  21 . For example, the operation unit  51  of the projector  2  may be used to set the timing for activating the lamps  21 . This also allows for the switching of the lamps  21  to be controlled based on the set timing. 
     Such a structure allows for the activation pattern of the lamps  21  to be set with further flexibility. Further, an activation pattern that activates the lamps  21  at timings desirable to the user may be generated. 
     In the first embodiment, in the same manner as in the second embodiment, the projector  2  may be configured so that when starting activation of the lamps  21 , a predetermined image is displayed until the illuminance of the lamp  21  that started activation stabilizes and so that the displayed image is switched after the illuminance of the lamp  21  stabilizes. Such a structure would obtain advantage (11), which is described above. 
     In the second embodiment, instead of the timings for switching the lamps  21 , time intervals for switching the lamps  21  may be set to set the activation period of the lamps  21 . 
     In the second embodiment, in the same manner as in the first embodiment, at least pat of the activation pattern of the lamps  21  may be set as a repeat pattern. In this case, the control unit  54  switches the lamps  21  in accordance with the repeat pattern. Such a structure would obtain advantage (6), which is described above. 
     The number of times for repeating the repeat pattern may be set in the same manner as in the first embodiment. In this case, the control unit  54  controls the switching of the lamps  21  so as to repeat the repeat pattern for the required number of times. Such a structure would obtain advantage (7), which is described above. 
     In each of the above embodiments, the user may selectively set either one of the switching time interval of the lamps  21  and the switching timing of the lamps  21 . Such a structure would allow for the activation period of the lamps  21  to be flexibly set. This would improve convenience for the user when setting the activation period. 
     A prism block, for example, may be used in lieu of the optical path switching device  24  so that the light emitted from the first lamp  21   a  and the light emitted from the second lamp  21   b  are both reflected by the prism block and guided to the image generation unit  25 . That is, the image generation unit  25  and the projection lens  26  may be shared in the optical paths formed by the plurality of lamps  21 . Thus, a device for switching the optical paths is not necessarily required. 
     Further, the present invention is not restricted to selectively switching a plurality of optical paths formed by the plurality of lamps  21 . That is, the present invention is not limited to alternate activation of the lamps  21 . As described above, when a prism block is used in lieu of the optical path switching device  24 , the plurality of lamps  21  (i.e., the first lamp  21   a  and the second lamps  21   b ) may be simultaneously activated. In this case, the lights simultaneously emitted from the lamps  21  are guided to the image generation unit  25 . Such a structure would improve the illuminance of the image in comparison to when activating just one lamp  21 . 
     The projector  2  is not limited to just two lamps and may include three or more lamps  21 . In this case, as described above, some of the three or more lamps  21  may be simultaneously activated. 
     The operation unit  51  of the projector  2  may be arranged on a remote controller that corresponds to the projector  2 . That is, the projector  2  may include a remote controller, and buttons arranged on the remote controller may form the operation unit  51 . 
     The video signal output unit  13 , the control signal input/output unit  16 , the video signal input unit  41 , the control signal input/output unit  53 , and the control signal input/output unit do not necessarily have to be formed by terminals connected to cables or the like and may be formed, for example, by a wireless communication module including an antenna. The input/output means may be either wired or wireless for signals between the computer  1  and the projector  2 , the computer  1  and the image reproduction device  6 , and the projector  2  and the image reproduction device  6 . 
     The signals input and output between the computer  1  and the projector  2  or between the projector  2  and the image reproduction device  6  are not limited to video signals, and audio signals may be input to the projector  2  together with video signals. In this case, sound may be reproduced with a speaker (not shown), which is an audio output device incorporated in the projector  2 . Further, the sound may be reproduced with other audio output devices. In this manner, the present invention is effective not only for digital signage including only video contents but also for digital signage including both video and audio contents. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.