question about Light Dependent Resistors or LDRs?

Question

i know that when the light intensity of a light source falling on an LDR is high, the resistance in the LDR falls and when the light intensity is low, the resistance of the LDR is high.
and i know that when resistance is high, current flowing through the LDR is low and vice versa.
however, whats the relationship between the voltage and the current in an LDR? are they directly or inversely proportional?
if the current in an LDR rises, will the potential difference also rise or fall?
this is quite important as i need it for this sensor i'm making at school.
if u've got ur information from a website, could you also mention the website here or create a link?
thanks

Answer 1

Depends on where you are measuring the voltage and what the rest of the circuit looks like. If you are measuring across the LDR, the voltage difference will drop as the current flow increases with lowered resistance. If you are measuring the potential to ground down stream of the LDR, the voltage should go up as the resistance drops.

Answer 2

It seems like you are over thinking this. The LDR is just a variable resistor. I'm sure you played with a potentiometer by now and that was a variable resistor. With the pot, you had to rotate the shaft to change the resistance. Well, the LDR doesn't have the shaft, but varies it resistance based on the amount of light it senses. So it might help you to think of the LDR as potentiometer (BTW, it is very useful to use a pot in place of this LDR when you are first building your circuit- easier to control a pot and all).

But basic electrical principle states, assuming everything else in the circuit stays the same, that voltage drop and current are inversely related through an element whose resistance changes.

Answer 3

They rely on light exciting electrons from the valence band or doping band to the conduction band of the material. These excited electrons ultimately decay back, but contribute to conductivity while they are in the conduction band. The balance between the rate at which light is exciting electrons (the luminosity) and the decay back determines the conductivity - and hence it depends on how much light there is.