A kind of backlight unit is designed in this paper

in which the white LEDs are used as the main light source

and the orange LEDs and blue LEDs are used as the color-complementation light source. The proportion of high levels of three PWM control pulses is gained on the condition of different lightness by the method of linear matching

and then the three PWM pulses can be adjusted according to the proportion. By this way

the standard white light source can be obtained

of which the color temperature

u'

is in 6 500100 K

the color coordinate

u'

is in 0.1980.01

and

v'

is in 0.4680.01. The high level time of three PWM pulses can be adjusted appropriately according to the color data of TCS230 when the temperature is changed. The color will keep steady on the condition of the pulses number of the three color channels keeping their proportion fixed.