Add motion sensor driven floodlights to existing "regular" outdoor lamp

Question

North American Wiring:

Let's say I have an outdoor lamp that turns on and off via a switch from the inside (something like pic below).

I want to add a motion (long-distance) sensor floodlight to this situation. Such that I still have an outdoor lamp that turns on and off via a switch from the inside, and additionally I have some kind of floodlight that turns on if it detects motion (up to about 70 feet), and only runs dusk-to-dawn.

The wiring for the floodlights will have to come from this existing lamp fixture.

I have never done electrical work. But I know how to turn off the mains and splice wires together.

If you've done something like this, please share how you did it. If you haven't, but have suggestions on fixtures / bulbs etc. please share (they're even making motion-sensitive bulbs these days).

Answer 1

Note: this answer assumes North American wiring. You don't give a location but that photo looks like an American fixture to me.

There are two ways the existing fixture may be wired. The first way is by "switch loop": Here, power enters at the fixture and a separate cable (switch loop) carries hot to the switch and switched hot back to the fixture. If this is what you have, your new wiring is easy: connect your new cable to the back, white and ground cables coming from the breaker panel (the wirenuts shown in the center of the diagram). This provides hot, neutral and ground for your new, unswitched floodlight.

However, you may instead have it wired that power comes to the switch first: This would be a problem because there isn't an always-on hot wire at the fixture. If you connect your floodlight to the fixture wires, it will only operate when the switch is on.

Assuming you don't want to change the existing wiring, the only answer I can see is to leave the switch always on and replace the existing fixture with a smart light that can be controlled through another means.