The "heating" methods - resistor/bulb/transistor - are frequency independent up to quite high frequencies.

For the "heating" methods (being that bulb, resistor or FET transistor) you can think of the thermal effects as of electric circuit - the source of the heat is like charge (current) source, its thermal inertia (together with the sensing element in case f resistor/transistor) is like a parallel capacitor, and the heat dissipation is like a resistor (of course you will want to have a stable "ground" - the heat dissipation should not change in time). You will easily see, that if you apply a heat/current pulse, it will somehow "spread" out on the capacitor. Integrating it you can obtain a value proportional of the total energy of the pulse. If you want to reduce the "spreading", you need to decrease the time constant of the setup. so you can either decrease the thermal capacity (decrease the total volume of resistor+fixture+temperature measuring element) or decrease the "resistance" = increase the heat dissipation (but it will decrease the sensitivity of the whole setup).

Jan Waclawek