A high intensity monochromator was designed which provides maximum versatility and flexibility in providing high intensity output of ultraviolet and visible light. The monochromator incorporates automatic calibration and direct recording of exposure intensity and duration. Output of the high intensity monochromator between 200 and 600 m[mu] is approximately twice the solar radiation at the earth''s surface assuming no atmospheric attenuation. Time required to give a minimal erythemal dose to untanned human skin of the abdomen is from 15 to 25 sec. but times as low as 4 to 6 sec. have been observed at 300 m[mu] using 50 Angstrom (A) bandwidth.