I have used the exact same LED light, and had the same thing happen, it would glow faintly for several minutes after it was turned off. I am guessing some kind of capacitor inside? I suppose it could be picking up induced voltage from the fixture wiring. Is the lamp plug polarized? Is the lamp fixture, and outlet wired correctly? I don't see any harm with it glowing dimly, but I agree it should not. I used mine as a nightlight for an average of 10 hours per day, and it stopped working after 3 months, or roughly 1000 hours. Considering it was rated for 20,000 hours, I was not pleased.

LEDs run on DC current, so there is a power supply in the unit to change the 120 V AC to some lower voltage DC.

Power supplies producing DC have filter capacitors to smooth out the pulses produced from the 120 V AC waveform.

These capacitors will slowly discharge after the AC input power is removed.

Thanks Brickeyee and Dan, but part of the puzzle is still missing:

After removing the bulb from the switched-off socket (ceiling fixture) it loses its glow in a minute or two. Upon replacing it in the switched-off fixture it begins to glow again.

Phantom voltage, faulty switch, induced current? I understand that it takes very little current to make these work, but why would there be any current at all in the turned off overhead?

Thanks again,

Mark

An LED will glow faintly with just a few microamps of current. Most likely you're getting a bit of capacitive coupling in the wiring, creating a miniscule amount of current leakage across the switch. It would never be enough to make an incandescent bulb glow, or even light a compact fluorescent. However, you can measure it with a high impedance meter, and I can imagine it making LEDs glow.

This could easily happen in a 3-way switch setup (with the travelers running parallel in a cable), or if the switch is on a switch loop.

It's nothing to worry about.

Is the switch for this light a lighted switch? These light up by allowing a small amount of current to leak, probably enough to faintly light the LED bulb.

could there be a sensor or touch lamp? there is usually a cad cell shorting a resistor in a sensor. Try unplugging the lamp or turning off the breaker. If it glows then, It is being induced from another wire.