LED light bulbs: when off isn't really off

TexasCamper · 08-26-2011, 06:37 PM

On my last camping trip I noticed that my outdoor patio light, recently fitted with an LED light bulb, was glowing even though the light switch was off. Upon closer inspection I noticed that 3 of the LEDs were illuminated. I turned the switch on, and all LED's became illuminated. I turned the switch off and once again, 3 LEDs were illuminated, although not as brightly. Bulb is a 21 led warm white board by command electronics. (model no. K-0031), relatively new.

I dismissed it until I noticed the same thing happen with one of my cheap LED flashlights.

Anyone seen this before or know why?

- John

**ShrimpBurrito** · 08-27-2011, 01:43 PM

I have the same K-0031 boards from Command Electronics, and I do not have this problem. But I don't understand how this could be a problem with the board -- when the switch is off, there should be zero power going to the LEDs. The only way I could see this happening is maybe a capacitor on the circuit board is somehow providing power, but even then, the LEDs should go off after some time.

Do you have other boards from them in your TM? If you do and this one is the only one that does this, call them and get it replaced.

Dave

Brittany Dogs · 08-27-2011, 03:08 PM

This is a long shot: but sometimes corrosion can be in a switch and conduct enough 12 volts that it could power some of the LED to a small amount. The corrosion is usually never conductive enough to light a filament bulb but might be acidic or salty enough to conduct enough current for LED’s.

Suggestion, if you have a digital volt meter which is usually very high impedance, such a meter when probed inside the light socket, might show a few volts with the switch off. This would be the clue that it could be enough to power the LED’s. The switch might need replacing or cleaning inside.

Again, I said this is a long shot….

scrubjaysnest · 08-28-2011, 07:00 AM

The only time I have seen this is when the board gets damp or wet, the vent lights are really prone to this if you leave a vent open

and it rains. Haven't had a problem with the vent lights since installed air max vent covers, even during a gully washer.

**Bill** · 08-28-2011, 01:36 PM

John -

I gotta go with Dave / Shrimp Burrito on this. Off is off - if there is no power to the board, the LEDs cannot be lit unless there is some on-board source of energy.

Early LED bulbs were very prone to burnout from momentary over-voltage conditions. If you search this board, you'll find some horror stories. Later on, the LED light manufacturers realized that this was a problem, and installed a voltage regulator as part of the LED module. The K-0031 boards have one - you can see it in the photos. The regulator has a big capacitor (energy storage) at its output, and it could store enough energy to power a LED, dimly, for many seconds. As a different example, the Power Indicator light on my laptop's wall wart glows for many seconds after I unplug it.

I can't know for sure, but I believe this is what you are seeing.

Bill

TexasCamper · 08-28-2011, 09:23 PM

I was wondering whether there was a capacitor on the LED board. But if that is the source of power, wouldn't it happen on the other boards (I have four of these)? Unless this board has a fault that makes its capacitor drain much slower vs. the others? And since this is only happening on the outside patio light, vs. the inside roof lights, I was suspicious on whether moisture was playing a role (e.g., like the switch corrosion idea).

....anyway, thanks for the ideas....I'll let you know what I find out next time I'm in the camper.

scrubjaysnest · 09-05-2011, 08:25 AM

a path of conductivity, usually a white film, across the on/off switch, again this is caused by water/moisture getting into the led housing. You might also have a condensation problem with the wall mounted switch by the door for the patio lights. LEDS draw such low current a pretty high path of resistance is all it will take.