Hi. I replaced all my fluorescent lamps (round) with LED's. I have noticed that about half seem to be faintly glowing when they are turned off. Recently I just touched a lamp and it weakly started glowing. What's happening? Polarity? 

LED lamps are strange beasts.

They are high impedance devises and will work, sort of, with very little current flow.

What you are seeing is possibly a bit of stray, cable induced, pickup from the house wiring.

Fitting an AC rated capacitor (for example a fan motor capacitor) across the light fitting terminals should fix this.

This ^^^.

 

But do verify that your switch is in the live side of the supply, a switched neutral can have similar effects.

2 hours ago, cooked said:

Hi. I replaced all my fluorescent lamps (round) with LED's. I have noticed that about half seem to be faintly glowing when they are turned off. Recently I just touched a lamp and it weakly started glowing. What's happening? Polarity? 

2 answers, 1 @Crossy has diagnosed, your neutral and line are crossed on half the lamps. The other is that you have bought cheaply designed/made lamps where the circuit doesn’t have the required resistor/capacitor that will prevent the glow.

Cheapest, reverse the wiring. Best, spend more per unit, though that is a bit of a lottery.

46 minutes ago, Crossy said:

 

But do verify that your switch is in the live side of the supply, a switched neutral can have similar effects.

Absolutely right although the question of "did the fluorescent lamps show similar problems?" would probably answer that.

I am assuming that there was no sign of ghostly glows before the LED's were fitted.

1 hour ago, Muhendis said:

Absolutely right although the question of "did the fluorescent lamps show similar problems?" would probably answer that.

Probably not as the leakage current required to light an LED is significant lower than required to light a fluorescent.

 

4 hours ago, cooked said:

What's happening?

did you remove the starters? (small round blueish things you can find on the side of your case... or just google if not sure)

the casings for regular fluresent lamps do support led's, but if they have starters then these need to be removed for the tubes to work.

 

There may be a 3rd possibility as some LED lamps are also made for safety exit use and are designed to provide limited light when power lost.  Not sure if they make for circle lights but have a few normal E27 base bulbs so designed.

37 minutes ago, sometimewoodworker said:

Probably not as the leakage current required to light an LED is significant lower than required to light a fluorescent.

True but if neutral is switched rather than live (see @Crossy comment above) then that is enough to make a fluorescent lamp glow quite nicely when switched off.

I know that to be true, been there done that.

4 hours ago, Pouatchee said:

 

did you remove the starters? (small round blueish things you can find on the side of your case... or just google if not sure)

the casings for regular fluresent lamps do support led's, but if they have starters then these need to be removed for the tubes to work.

 

Please note the original post

8 hours ago, cooked said:

I replaced all my fluorescent lamps (round) with LED's.

Might have some difficulty finding the starters in most of these.