If you switch on a light or other electrical device, you make it start working by operating a switch. She emptied both their mugs and switched on the electric kettle He pointed the light at his feet and tried to switch it on. = turn on
If you describe someone as switched-on, you mean that they are aware of the latest developments in a particular area or activity. I am very impressed with Brian Hanlon, who seems a switched-on sort of guy. quick to notice new ideas and fashions