Does the Node MCU v3 (LoLin) not have a builtin led?
the ESP8266 has a builtin led that is attached to D4 as labeled on LoLin boards which maps to GPIO2. One thing to Note is that the led is active low. In other words ... setting PIN 2 to '0' will turn the LED ON and setting PIN 2 to '1' will turn the LED OFF

Lolin Builtin_Led Picture

This is the only LED on the LoLin boards and differs from other devkits that have an LED on GPIO16.