Please explain human EM interference with my XMAS lights

[stevenstritt]

I am aware that the human body has electrical properties, But was baffled by what I witnessed Christmas Eve. I had a malfunctioning electric candle in the window. I picked it up to check the tightness of the bulb, and it immediately came on. I set it down and it went off. Three times this happened before I discovered that I did not even need to touch it, but merely move my hand close and it would light up. My question is how can so simple a device as a light bulb react this way, and why does this not happen all the time?

 

[berkeman]

I am aware that the human body has electrical properties, But was baffled by what I witnessed Christmas Eve. I had a malfunctioning electric candle in the window. I picked it up to check the tightness of the bulb, and it immediately came on. I set it down and it went off. Three times this happened before I discovered that I did not even need to touch it, but merely move my hand close and it would light up. My question is how can so simple a device as a light bulb react this way, and why does this not happen all the time?

Often with weird stuff like that, there is a floating CMOS logic input that is the cause. A floating CMOS logic gate input has very high input impedance, and static charge on your hand can generate enough of a field to push the gate input high and low. I've had this happen to me several times on prototype circuits where I wasn't paying attention and didn't tie off unused inputs.

How does this candle normally turn on and off? Does it have a button?

 

[stevenstritt]

There is no on/off switch
thanks

 

[berkeman]

There is no on/off switch
thanks

Was the bulb incandescent or LED? Does it still exhibit this weird behavior?

 

[stevenstritt]

It was incandescent. It was not actually at my house so I don't know. There were actually 3 lights behaving this way, and 3 others that didn't