Since the wavelengths of UV-C light are below the visible spectrum, it is unfortunately very difficult for an end-user without NIST calibrated equipment to visually tell the difference between 222nm, 254nm and 265nm lighting. The purple hue often emanating from UV-C lights is typically from imperfections in the bulb glass.  We had actually researched and developed higher purity glass solutions which improved lamp efficiencies but ultimately decided not to commercialize them after customers indicated they preferred the light as an indicator that the fixture was on.