Low humidity

Started 5 northern lights, now under t 5s. Humidity seams to be 20 percent. Is this bad? Should I get a humidifier? Any humidity tips I can use?

Ideally your humidity should stay between 40 and 50%. You can get away with 60% but that's getting close to running the risk of bud rot. You may experience slightly slower growth from low humidity but it won't harm your plants. And you will have to water more frequently with low humidity as well.