Humidifiers are very beneficial to growing indoors; whether in a grow room or a tent you are able to control factors related to air moisture. Even if you do not have electricity, you can always put up a DIY air humidifier.
Humidity is referred to as relative humidity (RH), indicating compared to the lightest possible humidity, with 100% meaning that water has fully saturated the air. This creates the possibility of rain. Warmer climates are more humid than cold as warmer air can hold more moisture.
A humidifier is an appliance that is electrical and its’ use is to raise the humidity levels in your grow room or tent. It does this by adding moisture to the air, such as evaporating water or through misting- depending on the model that you get. Many are automatic and incorporate a hygrometer (which measures humidity) to control their operation.
Besides the temperature, nutrients, grow lights, and soil- humidity is the other imperative part of your grow room. In fact, if humidity levels get below 30% RH, the growth of your plant will be stunted as photosynthesis has slowed down. You also may have too high of humidity, causing things such as mould.
The best RH range is reliant on many factors such as the stage of growth or age of the plant, as mature plants close to harvest require lower humidity levels than seedlings. Seedlings are looking for about 50-60% RH to start off the grow. The vegetative stage is entirely out of the seedling growth stage and humidity can be reduced a little to about 40-60% RH all throughout this phase. For the flowering step you are looking at even less humidity, somewhere about 40-50% RH. And for the late flowering stage 30-40% RH is optimal as you are really trying to avoid mould at this point.