Your break even point (cost of electricity saved vs cost of
Omron) comes out to about 4 years using rough estimates:
12 outages per year; 6 hours 27 minutes per outage;
15.5 W LED floodlight; $0.23 KWH average.
You can come to a more accurate number using the specs that
apply to you instead of the averages I used.
That assumes your cost is $10.00. It won't be, using the
Omron. You'll need to buy the proper fittings/rails/enclosures/
wire etc. You'll need to install it in a dry location - ie
indoors - which can add construction costs. If you jury rig
the thing it will likely be unsafe, and definitly be unsafe
as far as the NEC is concerned.
The best solution - if it exists - is to buy a floodlight that
is programmable the way you want it. What you (and I) have is
designed to be programmable via an on/off switch to do exactly
what you describe: a real brief power interruption turns the
light on until either the sun comes up or you turn off the
switch; an extended (several seconds) power interruption
enables the light to respond to motion. You can find the
description of that buried somewhere in the documentation that
applies to your light.
The REAL question is what is it worth to you to do about it?
I understand the attraction of looking for a "gizmo" to modify
what you've got. It can be hard to defeat that attraction.
Cold hard reality can help. Run the numbers for your floodlight
in your location. Think really hard about whether making things
unsafe - or potentially unsafe - is worth it. Think about how
much time and effort you have to put into it. There does come
a point where it is no longer fun.
Ed