A low concentration formulation for hydrophobic photosensitizers (PS) and method for photodynamic therapy (“PDT”) using the disclosed low concentration formulations provide for more accurate, more efficient and more convenient dosing. The inventive formulation (1) reduces the time for a therapeutically effective level of photosensitizer to accumulate in diseased tissue and (2) reduces the time for achieving a sufficient ratio of photosensitizer in diseased tissue vs. healthy tissue. The inventive formulation reduces the time interval between PS application/administration and irradiation (the drug-light interval or “DLI”) and can provide for a “same day” PDT treatment option. 0.08 mg/ml to 1.3 mg/ml meta Tetra-Hydroxy-Phenyl Chlorin (m-THPC) as the photosensitizer in a mixture of pure propylene glycol and ethanol (3:2 volume ratio) accumulates in diseased tissue and differentiates between diseased tissue and normal tissue sufficiently quickly for ‘one day’ or overnight administration and activation treatment procedures to be possible.