Silicon type photocells (tiny little solar cells, essentially) have
some of the same problems that power solar cells have - degraded
output current over time.

CDS (Cadmium Sulfide) should be much more stable over long periods of time.

As far as longevity, consult your manufacturer - some cheap ones last
forever, some expensive ones dies quickly, and vice-versa.  Horses for
courses...

-Adam

On 3/31/07, Peter Todd <pete@petertodd.ca> wrote:
> I have a few projects that I'm using cds-type photocell resistors in
> them. Specifically they are all digikey #PDV-P9001-ND in a simple
> voltage divider circuit. I'm running them to spec, 1ma max-current etc.
> They've all gotta last at least 10 years. My definition of failure would
> be their specs drifting by more than about 30% In the applications they
> are at worst completely uncovered and *may* be subject to UV light, but
> would generally be used in a standard office environment.
>
> I mentioned this to someone who said that photocells are unreliable and
> won't last more than a year or two. He said they all fail due to light
> exposure within a few years.
>
> Seems pretty dubious to me, photocells are used in streetlamps after
> all, and the datasheets don't mention anything worrying, but... What do
> you guys think?
>
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