Lux value read from Opt3001

Hi All,
Am trying to read the 16-bit register value from the opt3001 ALS sensor from the code posted below. Am getting the MSB 8-bit 
data properly but LSB value always 0xFF. Can anyone help me out in this issue weather am i reading register value properly?


void opt3001_read(void)
{
                                                                               // create an instance of MsgObj named msg
       uint8_t als_register_read[2] = {0x00,0x00};
       int lux;
       while(1){

              I2CMasterSlaveAddrSet(I2C6_BASE, SLAVE_ADDRESS, false);
              I2CMasterDataPut(I2C6_BASE, 0x00);               
              I2CMasterControl(I2C6_BASE, I2C_MASTER_CMD_BURST_SEND_START);
              while(I2CMasterBusy(I2C6_BASE));


              I2CMasterSlaveAddrSet(I2C6_BASE, SLAVE_ADDRESS, true);// true indicates that master is initiating the receive.
              I2CMasterControl(I2C6_BASE, I2C_MASTER_CMD_BURST_RECEIVE_START);
              while(I2CMasterBusy(I2C6_BASE));

              als_register_read[0] = I2CMasterDataGet(I2C6_BASE) ; //Receives a byte that has been sent to the I2C Master
           
              I2CMasterControl(I2C6_BASE, I2C_MASTER_CMD_BURST_RECEIVE_FINISH);
              while(I2CMasterBusy(I2C6_BASE));
              als_register_read[1] = I2CMasterDataGet(I2C6_BASE);

              lux =  0x0FFF & (uint16_t)als_register_read[0] << 8 | (uint16_t)als_register_read[1];
              int8_t exp = als_register_read[0]>> 4;  //exponent is top four bits
              lux = 0.01 * pow(2,exp) * lux;
       }
}