What Causes a Voltage in a Circuit with an LED and Filament Lamp?

[Mrs Moggins]

Does anybody know why illuminating an LED with a filament lamp would produce a voltage in a simple circuit with just an LED and voltmeter? I'm guessing it's related to the photo-electric effect, but I have no idea what is actually going on.

If any of you guys could help me out, or point me in the right direction, it would be a great help!

Thank you in advance!

 

[chroot]

It would only make sense -- if passing current through an LED produces light, why wouldn't shining light on an LED produce current?

It is, in fact, the photo-electric effect. An LED is basically just a p-n junction, comprised of two kinds of semiconductors joined together. The region around the junction is normally depleted of charge carriers, because free electrons on the n-side of the junction want to rush over into the electron-starved p-side.

When you shine light on the depletion region, the photo-electric effect kicks electrons out of atoms. These free electrons then immediately slide down the potential hill toward the p-side of the device, and a current flows.

- Warren

 

[Mrs Moggins]

Yeh, that seems to make sense. It was the point about the photoelectric effect freeing electrons in the depletion region that I was originally unsure about. Will white light incident on the depletion region definately free electrons from these otherwise stable atoms?

 

[chroot]

The frequency-sensitivity of an LED can be pretty complicated. A good thermal white light source should have enough light of every frequency to stimulate any LED to produce a measurable current.

- Warren

 

[Mrs Moggins]

Ah ok, so visible or even infrared light has enough energy to free these electrons. Thank you very much for your help, it really is appreciated!