SGX302 (0.25 % hypericin) ointment will be applied to lesions and treated with visible light 24±6 hours later starting at 5 J/cm^2. Drug application/light session will be done twice a week (at least 2 calendar days apart) for 18 weeks.

Placebo ointment will be applied to lesions and treated with visible light 24±6 hours later starting at 5 J/cm^2. Drug application/light session will be done twice a week (at least 2 calendar days apart) for 18 weeks.

SGX302 (0.25 % hypericin) gelt will be applied to lesions and treated with visible light 24±6 hours later starting at 5 J/cm^2. Drug application/light session will be done twice a week (at least 2 calendar days apart) for 18 weeks.

SGX302 is synthetic hypericin formulated as a 0.25% hypericin ointment or gel.

The percentage of patients in each treatment group that achieve a 0 or 1 score (Clear or Almost Clear) evaluation using the 5-point Investigator's Global Assessment (IGA) scale.

The 5-point IGA scale:

• Score 0: Clear - No signs of psoriasis; post-inflammatory hyperpigmentation may be present
• Score 1: Almost Clear - No thickening; normal to pink coloration; no to minimal focal scaling
• Score 2: Mild - Just detectable to mild thickening; pink to light red coloration; predominantly fine scaling
• Score 3: Moderate - Clear distinguishable to moderate thickening; dull to bright red; moderate scaling
• Score 4: Severe - Severe thickening with hard edges; bright to deep red coloration; severe/coarse scaling covering almost all lesions

The percentage of patients in each treatment group that achieve a ≥75% improvement in Psoriasis Area and Severity Index (PASI 75).

PASI is a combined assessment of lesion severity and affected area into a single score. The body is divided into 4 areas for scoring: head, arms, trunk and legs. Each area is scored by itself and scores are combined for a final PASI. For each area, scores of erythema, thickness and scale are scored on a scale of 0 (clear) to 4 (maximum). For each area, percent of skin involved is estimated: 0 = 0%, 1= 0 to ≤10%, 2 = 10 to <30%, 3 = 30 to <50%, 4 = 50 to <70%, 5 = 70 to ≤90%, 6 = 90 to100%. Final PASI = (sum of severity parameters for each area)*(area score weight of section (head: 0.1, arms: 0.2 body: 0.3 legs: 0.4)).