Time-Stable Red, Green, and Blue Light-Emitting Diode Backlighting Control Using Time-Varying Transform Matrix

o m p p c B bstract. This paper proposes a driving current control method for back light unit (BLU), consisting of red, green, and blue (RGB) ight-emitting diodes (LEDs), whereby a RGB optical sensor is used o check the output color stimulus variation to enable a time-stable olor stimulus for light emission by the RGB LED BLU. First, to btain the present color stimulus information of the RGB LED BLU, n RGB to XYZ transform matrix is derived to enable CIEXYZ vales to be calculated for the RGB LED BLU from the output values of RGB optical sensor. The elements of the RGB to XYZ transform atrix are polynomial coefficients resulting from a polynomial reression. Next, to obtain the proper duty control values for the curent supplied to the RGB LEDs, an XYZ to Duty transform matrix is erived to calculate the duty control values for the RGB LEDs from he target CIEXYZ values. The data used to derive the XYZ to Duty ransform matrix are the CIEXYZ values for the RGB LED BLU esimated from the output values of the RGB optical sensor and coresponding duty control values applied to the RGB LEDs for the resent, first preceding, and second preceding sequential check oints. With every fixed-interval check of the color stimulus of the GB LED BLU, the XYZ to Duty transform matrix changes daptively according to the present lighting condition of the RGB ED BLU, thereby allowing the RGB LED BLU to emit the target olor stimulus in a time-stable format, regardless of changes in the ighting condition of the RGB LEDs. © 2009 Society for Imaging cience and Technology. DOI: 10.2352/J.ImagingSci.Technol.2009.53.3.030503