Since the normal tissue retains little or none of the dye, it is not usually affected. The laser light application is always done in an operating room of the surgery department at the hospital. Occasionally small cancers can be treated as out patients. The fiber is then placed close to, or into the tumor to deliver the proper amount of light. Ordinary light, such as that from light bulbs is diffuse, meaning the light rays are scattered rather than focused.
Laser light is of a single wavelength - all the energy works together and in one direction.
Because laser light can be focused to a fine point and can be controlled so precisely, it is a very useful tool for surgery. There are many different types of lasers. The one we use in Photodynamic Therapy is the argon dye laser. In this case, the argon dye laser is used to produce red light. Some people confuse laser light with radiation, but these are not the same.