in order to be able in the case of uv high - power omni - directional radiators to direct the generated radiation only in a preferred direction , and to avoid shading by the inner dielectric tube , the outer electrodes are arranged only on a part of the circumference of the outer dielectric tubes . in this way , the object to be irradiated or the substance to be irradiated can thus be arranged directly in the range of emission of the discharges .