I have a light fitting with one CFL lamp and one LED lamp in it. I have noticed that when I switch off the CFL goes out immediately but the LED lamp fades out over perhaps one or two seconds.
I thought the CFL might continue to glow as the phosphor was still 'energised' - but it doesn't.
Maybe the LED lamp continues to glow because of a capacitor in the driver circuit otherwise an LED wouldn't glow without power. Would it?

 

It could be the caps in the LED slowly discharging if it eventually goes out. If the LED bulb lights dimly all the time, there may be enough capacitive coupling in the wires to supply a tiny current to the LED bulb.

 

It could be the caps in the LED slowly discharging if it eventually goes out. If the LED bulb lights dimly all the time, there may be enough capacitive coupling in the wires to supply a tiny current to the LED bulb.

It does go out completely fairly quickly.
The resaon I was doubtful about the capacitor was that I thought they used capacitor dropper supplies which wouldn't store charge.

 

There is often a smoothing cap.

Newer bulbs use a series of LEDs at line voltage, with a single linear current regulator chip.

 

I once swapped out an led bulb because it “wasn’t working”. When I picked up the “bad” bulb, it started glowing, like Uncle Fester’s light bulb.

 

LED lamps that do not include a switching power supply very often stay on when the light switch is off because of leakage current to earth. That leakage can come from a capacitance between one of the wires to earth. It does not take many microamps to make a good white LED glow visibly, especially in a darkened room.

 

LED lamps that do not include a switching power supply very often stay on when the light switch is off because of leakage current to earth. That leakage can come from a capacitance between one of the wires to earth. It does not take many microamps to make a good white LED glow visibly, especially in a darkened room.

It does go out completely quite quickly and the lighting circuit does not have any earth wire (!).

 

It is almost certainly just the smoothing cap on the supply. To save money, they often omit the bleeder resistor and as mentioned the LED can light at very low currents.

 

I have the same phenomena in all my LED light panels. Switch them off and they fade to off over about 1 1/2 seconds.

The LED's I have in the laundry room are different. They're controlled by a motion sensitive switch. When no motion is detected the LED's may flicker or remain about 40% lit. The only way to get them to go fully out is to put an incandescent lamp in the circuit. The cause is somehow related to the type of switching circuit in the PIR switch.

 

White LED's do use a phosphor coating over a UV LED to get broad band white emissions. This will be evident in a low intensity glow once a white LED is turned off. That being said, I've seen LED lamps stay on for nearly a second or so after power has been removed. I figured that was a cap in the power supply.

 

MOST LED lights will dime because they do use at least one capacitor. And likewise many CFL devices, although the dimming time is usually much to short to notice. This is seldom a problem, except with flasher applications.