Using the Specific Heat Formula, I found that I need to apply 612J of heat to melt 18g of marshmallow. Marshmallow has a specific heat of 2 J/(g*C), melting point of 98.6°F, and a starting room temperature of 68°F. I found a heat lamp generates up to 150 watts of power via radiation, which means it can melt the marshmallow in 4 seconds (according to Time (s) = energy required (J) / power (W)).
5 seconds seems too good to be true. I am assuming perfect transfer of heat from lamp to marshmallow, but even after considering 50% efficiency, it only takes 8 seconds.
Does this make sense or did I miss something obvious? Thanks!!