After three days of fighting: they own the basements and the night. During the day, everything where sunlight falls is ours. It makes them lethargic, stupid, they can’t fight. Their beam weapons go unused, they sit stupefied where they are and wait for us to come finish them.
At night, or underground, they cut through us like a harvester through wheat. If they’d landed during the winter, with shorter days, we might already have lost everything.
We’re booby-trapping underground areas as we fall back, but our most precious weapon in the struggle to retain Earth might just be the sunlamp.