wrote in message
oups.com...
My wife bought a "security light" at Costco, to be installed above the
garage door, below the eve of the roof. It's a basic model, with two
bulbs, probably no more than $50. We did not previously have an exterior
light above the garage door, so
there was no electrical outlet. Inside the garage, there was an
available outlet, about 5 feet away from the door. So, I bought a cheap
extension cord, plugged the pronged end in the outlet.

This is no way to hook up an exterior light, period. Not safe, with rain and
no ground, not in code, and not weatherproof. You need to run a proper
behind-the-wall Romex or conduit to the site, install a junction box, and do
it right, with groundwire weatherproof gasket, and all. Cheap light units
may flicker when the sun sensor cannot decide what light level is outside,
or the level adjustment needs twiddling.. Home Depot sells a 50-70 buck
motion sensor light by Heath or Stanley called the JourneyMan, with lifetime
unconditional guarantee. Thier sun sensor seems pretty robust, as I have had
three units for six years, and seem to work flawlessly, in spite of being
imports. Inexpensive security lights tend to have early failures in my
experience, but both your door reflectivity and the way it is hooked up
without a ground may be inducing flickering.