Yes, ideally you want your humidity between 40%-60% for the vegetative growth phase, and 30%-40% during the flowering phase. Humidity has an effect on a plants growth rate and overall health. It affects transpiration as well as photosynthesis. Higher humidity levels encourage mold and fungus growth, and low humidity levels make your plants more susceptible to heat stress and burning. For optimum health and growth rate, you really want to get yourself a cheap humidifier so that you can raise the humidity up to the appropriate range.