I have a light out back of my house on a detached garage that lights up the
parking area. I would like to run it off of a mechanical timer so it goes on
at 5 p.m. and off at 10 p.m. I would also like to put a photocell on the
light so that if it isn't dark at 5 p.m. the light won't come on. Now, I
would also like to put a motion detector on the light so that after 10 p.m.
when the timer shuts off the light will come back on in case I get home
after 10 or someone trying to get in my garage would set it off.

If I feed the light from two different sources (same circuit) one through
the timer and photocell and one through the motion detector, would I achieve
my goal? Will there be a problem with each source backfeeding through the
other. I can't imagine the mechanical timer will be bothered by the load
side being hot but I'm not so sure about the photocell or the motion
detector. Could I (should I) put diodes in to keep them from backfeeding
each other? I won't be putting more than a 100-watt bulb in the fixture.

Thanks for any help,
Dave