A display apparatus comprising: display means for displaying an image; a light source including color LEDs of three different colors that irradiates light to the display means; and control means adapted to control the quantity of light of the light source with pulse width modulation, wherein the control means is further adapted to control the quantity of light of the light source by varying the ratio of a light-on period, during which the light source is repeatedly turned on and off using the pulse width modulation, to a light-off period, during which the pulse width modulation is inactive and thus the light source remains off for an interval that is longer than any interval that the light source is turned off using the pulse width modulation, characterized in that it further comprises: light receiving means 5comprising a color photo sensor adapted to detect a detection value corresponding to the quantity of light of the light source; and a switch provided between the light receiving means and an A/D converter, said switch being configured to be closed in response to a sampling pulse from said control means and to transmit the detection value of said light receiving means to said A/D converter which is configured to output digital signal, corresponding to said detection value, which is fed back to said control means, wherein the control means is configured to give said sampling pulse to the switch to detect the detection value corresponding to the quantity of light received by the light receiving means within the light-on period and wherein in order to adjust the quantity of light of the light source to at least a predefined quantity of light or larger, the control means is configured to control the quantity of light of the light source by adjusting the pulse width while keeping the light-on period at 100% and the light-off period at 0% until the pulse width of pulse width modulation corresponding to the predefined quantity of light is obtained, and, in order to adjust the quantity of light of the light source to the quantity of light smaller than the predefined quantity of light, the control means is configured to control the quantity of light of the light source by varying the ratio of the light-on period to the light-off period while keeping the pulse width constant at the said pulse width of pulse width modulation corresponding to the predefined quantity of light during light-on periods. display means for displaying an image; a light source including color LEDs of three different colors that irradiates light to the display means; and control means adapted to control the quantity of light of the light source with pulse width modulation, wherein the control means is further adapted to control the quantity of light of the light source by varying the ratio of a light-on period, during which the light source is repeatedly turned on and off using the pulse width modulation, to a light-off period, during which the pulse width modulation is inactive and thus the light source remains off for an interval that is longer than any interval that the light source is turned off using the pulse width modulation, characterized in that it further comprises: light receiving means 5comprising a color photo sensor adapted to detect a detection value corresponding to the quantity of light of the light source; and a switch provided between the light receiving means and an A/D converter, said switch being configured to be closed in response to a sampling pulse from said control means and to transmit the detection value of said light receiving means to said A/D converter which is configured to output digital signal, corresponding to said detection value, which is fed back to said control means, light receiving means 5comprising a color photo sensor adapted to detect a detection value corresponding to the quantity of light of the light source; and a switch provided between the light receiving means and an A/D converter, said switch being configured to be closed in response to a sampling pulse from said control means and to transmit the detection value of said light receiving means to said A/D converter which is configured to output digital signal, corresponding to said detection value, which is fed back to said control means, wherein the control means is configured to give said sampling pulse to the switch to detect the detection value corresponding to the quantity of light received by the light receiving means within the light-on period and wherein in order to adjust the quantity of light of the light source to at least a predefined quantity of light or larger, the control means is configured to control the quantity of light of the light source by adjusting the pulse width while keeping the light-on period at 100% and the light-off period at 0% until the pulse width of pulse width modulation corresponding to the predefined quantity of light is obtained, and, in order to adjust the quantity of light of the light source to the quantity of light smaller than the predefined quantity of light, the control means is configured to control the quantity of light of the light source by varying the ratio of the light-on period to the light-off period while keeping the pulse width constant at the said pulse width of pulse width modulation corresponding to the predefined quantity of light during light-on periods.