Incandescent bulbs work, LED do NOT work

I had an experience with a home AC fixture having the same problem. A seniors forum acquaintance had bought a new LED fixture to replace an old incandescent one at the foot of the basement stairs. My first thought was that the new LED was defective. I brought a cord with me, hooked The LED light up to the cord and plugged it in - worked perfectly. Next I checked the voltage on the black to white wires coming out of the electrical box in the ceiling - 120 volts. Hooked up the fixture - No light. Took it down and by some fortunate accident I was a bit rough on the black wire and it pulled out of a wire nut connected it to the black wire from the breaker box.

I tossed the pigtail wire and connected the wire from the LED fixture to the service wire with the same wire nut and the LED light worked perfectly. Just a loose connection problem.