okay, thank you both!
I think I have a better understanding. So since R = V/I , because Voltage is at 5V, increasing the resistance will only decrease I. That makes sense and explains the LED.
To clarify the resistor was connected to the output of a Infrared Receiver, while the LED was on Pin 13 on the board.
You mentioned for a green LED the Vf is 3.5V. Is it possible to measure the Vf of my IR receiver or other devices, perhaps using a multimeter ?