Based on the Nest API documentation I don’t think they expose motion and lux. Based on the developer API reference guide found here Nest Developers and documentation here Smoke+CO Alarm  | Nest Developers
You can see below there is no motion or lux exposed for the Nest Protects.
“smoke_co_alarms”: {
“RTMTKxsQTCxzVcsySOHPxKoF4OyCifrs”: {
“device_id”: “RTMTKxsQTCxzVcsySOHPxKoF4OyCifrs”,
“locale”: “en-US”,
“software_version”: “1.01”,
“structure_id”: “VqFabWH21nwVyd4RWgJgNb292wa7hG_dUwo2i2SG7j3-BOLY0BA4sw”,
“name”: “Hallway (upstairs)”,
“name_long”: “Hallway Protect (upstairs)”,
“last_connection”: “2016-10-31T23:59:59.000Z”,
“is_online”: true,
“battery_health”: “ok”,
“co_alarm_state”: “ok”,
“smoke_alarm_state”: “ok”,
“is_manual_test_active”: true,
“last_manual_test_time”: “2016-10-31T23:59:59.000Z”,
“ui_color_state”: “gray”,
“where_id”: “UNCBGUnN24…”,
“where_name”: “Hallway”
}
},
