Can solar lights work in the dark?

Yes, the panels charge batteries that will allow it to work in the dark, until the charge runs out.

Yes. They put out light in the dark of night and then they charge up when the Sun comes up.

Solar lights collect solar photon energy during the day through their solar panel. This energy is converted into electricity and stored in the rechargeable (usually Ni-Cad) batteries. A photocell sensor detects whether there is sunlight available or not and acts to switch the lights on based on this. The electricity stored in the battery is regulated by a control board and, at night, the charged batteries provide power for the LED light. Once daylight returns, the panels repeat the process of charge.