The aim of this study is to evaluate the efficacy and safety of blue light with a high peak-intensity of 600 mW/cm² at different durations of treatment of mild Psoriasis vulgaris, compared to a topical vitamin D3-analogue (calcipotriol) treatment. In 2016 a monocentric, prospective, randomized, intra-individual study assessed the efficacy and safety of localized blue light treatment versus topical calcipotriol (Daivonex) treatment for mild Psoriasis vulgaris (Pv). 51 patients with mild Pv were randomized into two treatment groups, receiving 600 mW/cm² blue light either for 30 min (group30) or 15 min (group15) on one localised plaque, daily for 12 weeks, at home. This was compared intra-individually with a contralateral plaque treated daily with topical calcipotriol (Daivonex). Psoriasis severity was assessed by the investigator by applying the Local Psoriasis Severity Index (LPSI) and by the patient using a 100 mm visual analogue scale (VAS). Additionally, the Dermatology Life Quality Index (DLQI) was measured at different time points. The LPSI significantly decreased in both irradiated and comparator areas in group15 and in group30 patients. No difference between blue light and topical calcipotriol treatments was detected. Psoriasis severity VAS scale values assessed by the patients were significantly reduced in both groups (15 and 30 min) with a slightly, but insignificantly better outcome in group30. The DLQI was reduced by -1.76 in group15 compared to -3.39 points in group30. No adverse device effects were seen during the study other than a slight hyperpigmentation. Daily treatment for 12 weeks with blue light for 15 and 30 minutes is as efficient and safe as standard treatment for mild Psoriasis vulgaris with calcipotriol.