A fluorescent lamp that one would attach to furniture probably only takes 10W. That's less than 100mA at 120V; a telephone wire can handle that. Also, telephone wires once carried as much as 50VDC for ringers, so I'd expect the insulation to be adequate, if only barely. The biggest problem, I think, is that because the insulation is relatively thin, there's a greater risk of mechanical damage to it.