A 35 watt incandescent “decorative” bulb, dialed down to about 15 watts with a dimmer.
From my experience and from other accounts, it is 100% effective at preventing entry of opossums into a small outdoor pen where there are easy obvious entry points.
The roof is 1/3rd covered by black...
I have regular nightly opossom visits and they kill any chickens they can and also they can enter if there is any possible way. I think killing the opossoms would be useless since there is an "unlimited" supply in the region.
But on the advice of locals I installed a low level "artistic" light...