Lighting – ornamental security light

Assuming you're talking about motion sensors like this:

Switches like that need power. They can work by trickling current through incandescents if hooked up like a normal single-throw switch (in series with feed going to lights). If the switch has 4 wires (hot, return, switched, and ground) then you can hook them all up and it will power itself using it's own hot + return. In that case, it shouldn't have to trickle power through the light's circuit, and fluorescents should be able to turn off.

I think your strategy of making a cone out of aluminum foil was on the right track, but your choice of material was not. Think about what happens when you put various materials in the microwave. Paper, glass, ceramic: no effect, these will be ineffective. Aluminum foil: unintended consequences, do not use. Then consider what the microwave itself is made out of. You are essentially making the window (which is a person window, the negative image of a sensor window) This suggests the use of a grounded metal mesh or foam. Locally in NYC, the SpyStore sells copper-nickel mesh fabric for unstated purpose. You should also be able to find self-adhesive EMI/RF shielding foam at various industrial suppliers such as McMaster-Carr. You will want to wire either material to ground. I would start by trying to disable the sensor completely by this method (of covering it with grounded metal mesh or foam.) Then open a small aperture in the opposite direction of the corridor. Increase the size of the aperture until the functionality is as you desire. Use white self-adhesive paper label stock cut slightly larger than your masking material to return the sensor to an all white appearance if that is important.