I come from a ballet background, where the studios are surrounded with mirrors, so that you can see your alignment. It was quite a difference when I walked into my first yoga class and saw that there where no mirrors.  Most gyms, studios, pilates,martial arts, even cycling classes have mirrors but you will not find mirrors in a proper yoga studio. The reason for this is so that you can internalize your practice and feel your alignmnet.  Not to be distracted by how you look, whether it be good or bad.  It also encourages you to not look at what others are doing and focus on yourself. Yoga seems to be the only practice that I have seen that really encourages this.  Creating judjment upon yourself or others should be avoided regardless but not having mirrors helps to  create a safe environment to practice and focus on the inside of yourself. Also each pose has an eye focus or drishti, where your gaze should be to complete eash pose or asana. Put a mirror in front of you and your gaze will no doubt be your own eyeline or maybe the incredible yogi behind you, hence bringing you out of the pose and losing the whole purpose of practicing yoga. That is why yoga is called a practice for your mind, body, and spirit.  Without mirrors there is less judgment and without the judgmnet then there can be more light.  Light that you create inside of yourself that through repetative practice creates an external glow so that when you do see yourself in a mirror or look at others you are more likely to see the light in yourself and them.  Generating more light into the world one class at a time. - A mind free from all disturbances is Yoga. The Yoga Sutras of Patanjali