The betta won't neccessarily appreciate extra light if you have a light in your room and its not too dark or too bright (as in your fish can see properly), and if you have a heater to keep the water warm. Lamps are just extra effort (in a betta tank & if you don't have plants) IMOIf you just have like a little lamp you could put over the tank the Betta would appreciate some light, but you don't have to get anything extra.