UV lamps are made using a fluorescent tube without fluorescent coating, quartz or Vycor glass, because normal glass absorbs UVC rays. These lamps emit ultraviolet light with two peaks in the UVC range at 253.7nm and 185nm due to the mercury in the lamp and the visible light. 85% to 90% of the UV radiation generated by these lamps is 253.7 nm, while only 5-10% is 185 nm. These tubes have two to three times the UVC power of a normal fluorescent tube. These low pressure lamps have a typical efficiency of about 30 to 40%, which means that they produce about 30 to 40 watts of total UV energy per 100 watts of energy consumed by the lamp. Due to the other spectral lines of mercury, they also emit visible bluish white light. These "germicidal" lamps are widely used to disinfect surfaces in laboratories and the food industry and to disinfect the water supply.
