It is a birthday gift that Spencer gave to his sister, Carly (who had been wanting to have a lamp in her room for a long time). Spencer told Gibby to put the lamp and turn on the light in Carly's room, due to overheat, the lamp bulb exploded and burned the entire room (which causes Carly to fall into a deep depression for what happened).
After a couple days, Spencer rebuilt Carly's room (using the $82,000 he got from the diamond-encrusted wrist watch that was incinerated by the fire) and replaced the gummy bear lamp with a gummy bear chandelier.
Gummy Bear ChandelierThe Gummy Bear Chandelier is another piece of artwork made by Spencer that is also made out of multi-colored gummy bears; to replace the burnt lamp (that caused the accidental fire in Carly's room) he made for Carly. It first appeared in the episode, iGot a Hot Room, and it also made some reappearances in several episodes in Season 4 of iCarly.
You can buy a chandelier just like this one along with other items similar to those in Carly's room at http://jellio.com/store.html.