ILI9341 LCD backligh control

I have been looking at this data sheet and it appears as though you can control the backlight LEDs, i.e. the white LEDs behind the actual LCD screen (I assume).

It says that the backlight in controlled via registers BHf and 53h.

Is it possible to turn those LEDs off via these or other registers?

I have tried the following but none of it seems to have any effect:

void Adafruit_TFTLCD::displayOn()
{
 writeRegister8(ILI9341_DISPLAYON, 0);
}

void Adafruit_TFTLCD::displayOff()
{
 writeRegister8(ILI9341_DISPLAYOFF, 0);
}

void Adafruit_TFTLCD::backlightOn()
{
 //uint8_t nVal = readReg(0x53);
 //writeRegister8(0x53, nVal | 0b00001000);
 writeRegister8(0x51, 0xFF);
}

void Adafruit_TFTLCD::backlightOff()
{
 uint8_t nVal = readReg(0x53);
 //writeRegister8(0x53, nVal & 0b11110111);
 writeRegister8(0x53, nVal & 0b11111111);
 writeRegister8(0x51, 0x00);
}