Do I have to undress for Light Therapy to be effective?

Yes, it might be advantageous to undress for a Red Light Therapy session. While the Near Infrared light penetrates lighter materials, the red light is hindered by clothing. You can easily tell if the light penetrates your clothes as it gives off a red glow. Even if clothing reduces the Red Light Therapy effect, you can always compensate with a longer session to receive sufficient effect. There might be times when some light clothing is warranted, so it is better to
have a session with clothes on than no session at all.