In order to achieve high dynamic range (HDR) displays, the backlight LEDs of monitors need to increase the drive current to improve the luminous intensity. However, LED efficiency will be decreased with the increasing of current, and a fourth primary colour (orange) was introduced to mitigate the decrease of efficiency. Energy saving was achieved by mixing four primary colours and the brightness was allocated to different groups of three primary colour LEDs to reduce the drive current. Results show that the maximum power consumption can be reduced by 23.7% at HDR brightness of 1000 cd/m2, and the average power consumption reduced by 10.97%. In addition to the brightness allocation method, this paper also investigated the effect of improving the LED"green gap"on mitigating the efficiency decline.Compared with the power consumption of this scheme, the proposed method is 5 percentage points lower in white conditions and more than 3 percentage points lower in other situations, once again verifying the superiority of the proposed method in existing methods.