For what duration can I use my Edison the Medium?

You can use the Edison the Medium as long as the powercord is plugged in and the on/off button on the bottom of the lamp is on. Check if the Edison is in use, at least on the lowest light level (light lights up 15%). 

The brightness can be regulated by pressing and hold the "+" or the "-" button on the remote control or just use the on/off button on the lamp.