C’è del gas all’interno di una lampadina?

Students at their last year in high-school measure the temperature in different points of a lighted incandescent lamp bulb oriented in different directions and always find the highest temperature at the top. When asked why, their answers reveal interesting patterns of reasoning: heat goes up (without further explanation); the bulb contains air; the inert gas in the bulb is stationary and stratified according to temperature; some students only consider convection, others only radiation.