The design of the study consists of a total of 4 visits within a two week period. The first visit consists of VL+UVA1 irradiation with different light source on the opposite site of patients' back. A combination of non-invasive measurements (e.g., photography, redness and color changes of the skin using colorimetry and diffuse reflectance spectrometry) will be conducted throughout the 4 visits. Biopsies will be taken at various time points.
