Due to an experiment, I need a small heater (around 70 to 100 watts). I intend to use an incandescent bulb so it can act as a heater. What I wonder here is will a 70 watts Incandescent Bulb be equal to a 70 watts heater?
Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light.
So, yes, the incandescent bulb can be used as a heater and, in fact, has been used as a heater. For example, see: Easy-Bake oven.
The original toy used an ordinary incandescent light bulb as a heat source
Whatever bulb is used, basically all the power consumed will go into heating the environment, with the notable exception being any photons that escape through a window or some such thing.
Different styles of bulb have different visible light-heat ratios, but even the visible light emitted will simply bounce around the room a few times and deposit all its useful energy into random thermal motions. You know these photons cease existing, at least in the visible range, because when you turn off a light, the room essentially instantly goes dark.
Incandescent bulbs work better at heating than, e.g., certain fluorescent bulbs for a given amount of visible lighting because they consume more power (and thus emit more direct heat) per unit desired light. However, even if you designed a light bulb that emitted 100% of its photons in the visible range, that power (small though it would be) would all go into heating its environment.