How is Blue Light Different than PDT?

Blue Light therapy and Photodynamic Therapy (PDT) are both effective therapies for the treatment of acne. However, they are often confused with each other. Blue Light therapy and PDT both use a blue LED light as a major part of the treatment process. So what is the difference between blue light therapy and PDT?
blue light therapy utilizes a blue LED light, which is focused directly on the skin for a set amount of time. Blue LED light is proven to be antibacterial and to reduce the acne-causing p. acnes bacteria on the skin. Because blue light frequencies effectively destroy bacteria, many dermatologists report patients treated with narrow-band blue light show significant improvement in acne conditions. blue light treatment is sometimes combined with red light therapy, with decreases inflammation on the skin.
photodynamic therapy pdt is a procedure that uses a photosensitizing drug to apply light therapy selectively to target pre-skin cancer, acne and sun damage. PDT uses blue LED light in a different way. A light-sensitizing medication, called aminolevulinic acid, is applied to the skin and allowed to absorb into the follicles. The blue LED light is then used to activate the medication. This process not only kills the acne-causing bacteria, but it decreases excess sebum (oil) production on the skin. pdt treatment is one of the few acne treatments that can actually decrease the activity of the sebaceous glands (the oil producing glands). Besides blue light, multiple different light sources can be used including red light, intense pulsed light, pulsed dye laser and some others.
Photodynamic Therapy (PDT) is the most recent advance in acne therapy. Apart from acne, PDT can be used to treat many other skin conditions such as sun-damage, pre-cancer and even some types of skin cancer.