Sounds to me like you've bolloxed up the programming You need to get teh light to true max output.. I don't know what mode you have it in, but you can immediately get your LF3XT to full brightness by turning it on and then either holding the button down to get max (if it's in CUI), or by click holding (if it's in FUI). Check how full brightness compares to your nitecore then.
That's not quite correct. Turn on the light, with a quck click and release. If you are in the CUI (the default mode of a new light), it should turn on in the user defined mode. Now to get to the CUI's Max mode: Click, then quickly release, and quickly Press and HOLD. The light will go to full MAX, then release and it will stay in Max, until you issue another command to switch it to another mode, or you turn off and then on the light, where it will go back to the default user defined light level.
If you have some how gotten into the FUI (you would have had to do 5 consecutive clicks followed by a PRESS HOLD), you will know tha if one of the default levels is a flashing beacon. Double click to switch modes, and if you don't see a flashing beacon you are probably still in the CUI. If you happen to be in the FUI, do a PRESS (don't release) and HOLD the button down continuously. As long as you hold it you should see maximum brightness. This is a maximum momentary, which means it only stays in max as long as you keep the button pressed. Release the button and it goes back to the mode you were in before.
One other thing. It is pretty easy to have accidentally toggled on your momentary, which could also be confusing you when trying to issue commands. You know you are in momentary if with the light off, a firm press and hold turns on the light but then releasing turns off the light. A single quick click and then a release will turn the light on continuously. Then do 4 clicks in fairly rapid succession and you can toggle off the momentary.
If you are still having problems PM me. I am sure I can help you. We may have to connect by phone and I can walk you through it.