> Sounds like a product to develop, especially if the output were
> logarithmic and you could send it some sort of offset. A photo diode
> would be best for that, having more range than a phototransitor.

Well, a strange idea initially crossed my mind - use something like a
PIC12C508/JW with its window uncovered for the sensor, basing its output on
its initial RAM contents, which I believe is rather light-dependent (more
light -> less randomness).  However, I don't know if this effect is
repeatable enough to be useful, and I was hoping for a solution that costs
less than what a windowed PIC does...

Hey, weirder things have been done - anybody remember that long-ago article
(in Popular Electronics, I believe) for making a solid-state camera by
removing the top of a certain brand of RAM chip?
        Jason Harper