I found it!
root@LGwebOSTV:~# luna-send -i -f 'luna://com.webos.service.pqcontroller/getEyeqSensorData' '{"subscribe" : true}'
{
"backlightValue": 100,
"Eyeqsensorcheck": true,
"returnValue": true
}
{
"sensorDataCount": 2,
"backlightValue": 49,
"sensorData": {
"luminance": 27,
"visibleLuminance": 25
},
"returnValue": true,
"Eyeqsensorcheck": true
}