Vaporizers use heat. Humidifiers are devices that increase water content of the air in a room. Vaporizers are humidifiers are humidifiers that do this by heating the water. Cool mist humidifiers give the same result without heating. They work just as well. Avoid vaporizers. If you knock one over in the dark you may burn you feet and your shins.
Size of water. A simple humidifier (h)is composed of a water tank, a fabric or metal wick and a fan that draws room air through the wick to add water (humidity) to the air. The particle size is tiny & not visible. A vaporizer (v) is composed of a water source & a vibrating tuning fork device that creates visible vapor. While a v can also humidify a room, a h cannot produce visible vapor.