Okay, I haven't had time to get by the candy store, so I still don't have
the MOSFET recommended, and am still tinkering with this project out of my
junkbox. Problem is, it's not working right, and I can't figure out why.
Details a the photoresistor (and every photoresistor I have) DROPS it's
resistance in sunlight, rather than raising it, so the transistor conducts
when exposed to sunlight only. I replaced the photoresistor with a device
that seems to be a tiny photocell behind a window (with leads, and sized
similarly to the photoresistor) which provides .4VDC in normally bright
light, installed in polarity opposite to that which would assist Q1 in
conducting. My calculations (obviously flawed, but I can't figure out
where) tell me that it should counteract some of the voltage resulting form
the 4.2K/680 voltage divider, and keep Q1 from conducting in normal
sunlight. My numbers say there should be -.7VDC from the voltage divider,
and the photocell shouldmake that -.3VDC, which should turn Q1 off. Only it
doesn't seem to work that way. Q1 conducts regardless. What am I doing
wrong? I have verified the actual voltages at the base of Q1 (the juncture
of the voltage divider) and coming from the tiny photocell. Only nothing
changes. Could the problem be the miniscule current coming from the tiny
photocell? I somehow thought voltage was voltage, and current didn't
matter...

Attached is my schematic of the current configuration. Haven't bothered to
convert it to LTSpice, as I have no idea how to incorporate a solar cell,
sunlight, or the photocell on the PC board.

Ignorantly yours...

Dave