On Mon, 06 Apr 2009 22:43:57 -0400, wrote:

On Mon, 06 Apr 2009 17:05:08 -0400, "Percival P. Cassidy"
wrote:

On 04/05/09 04:43 pm bob haller wrote:

I replaced some existing incandescent bulbs by LED bulbs, then noticed
that they do not switch off completely but still glow dimly.

Checking the voltage at the lamp socket with a high-resistance
electronic multimeter, I get a reading of 48v!! A few volts might be OK
-- induction, stray voltages, etc., but 48V!!!

This occurs in two different rooms, but I think the various lighting
circuits are all connected to one breaker.

What could cause this?

its the meter, take a walk around high sensitivity meters will show 60
volts under the neighborhood power line........

connect a 100 watt light bulb with the meter voltage will go away.

relax yours must be one of the most frequent questions asked.

OK, but

(1) there are no overhead power lines within a mile. Walking around the
house with that meter and a lead trailing like an antenna I see not even
a 1 volt reading.

(2) It's a pain that the LED lights don't switch off completely. The
voltage with the switch off is sufficient to keep them glowing dimly.
Perhaps replacing one of the bulbs by a low-wattage incandescent would
hold the voltage down, but that offsets the power saving benefit of the
LEDs.

Perce


Cover the bulb - make it completely dark - the voltage will likely go
away. You are LIKELY getting a DC voltage FROM the light because an
LED is ALSO a photocell. An LED will produce a DC voltage when exposed
to light.
Green ones are Gallium Phosphide and make 1.65 to 1.74 volts each.
Not sure what the white ones are and what voltage they produce but I
think they are Indium Gallium Nitride - so likely around the same
output.


And remember - White LEDs also have a phosphorescent material in them
that makes white light from blue - the Phospor actually produces a
yellow light.