>
>
>> Photocells convert light to electrical energy, and don't operate on
>> varying
>> resistance.
>
> I don't understand what you mean by this. I was looking at the
> datasheet for
> PDV-P9001 for example and it even calls it a "light dependent resistor".


Then it is just that, a  LDR (light dependent resistor). Simply put,
photocells,  photo diodes and photo transistors works on voltage
generated by light, or voltage passed through a gate based on amount of
light on the base. It is normally silicon based.
LDR changes the resistance across it based on the amount of light. Easy
to see if you got an example, with a LDR you will see a small "grid" or
what looks like a couple of lines if you look through the lens (when
light falls on these lines, it changes the resistance between the lines).
When you look at a photo cell/diode/transistor you will see a small
(microns) block of silicon.
 Oh and a photocell differ from a diode/transistor in that is is made to
generate electricity, a photo diode/transistor works on the same
principal, but in microvolts.

It's been a while, anybody is welcome to correct me or expand on this.

Quentin

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