Abstract: An ultraviolet liquid purification system includes a purification chamber having banks of ultraviolet lamps distributed therein for applying germicidal ultraviolet radiation to the liquid flowing through in said chamber. Ultraviolet photocell detectors are located in said chamber to detect the level of ultraviolet radiation transmitted through the quartz jacket housing the ultraviolet lamps and through the liquid being purified. Indicator means produce an alarm signal when the total ultraviolet radiation transmitted through the liquid drops below a preselected level. In addition, a light conducting fiber is provided for each ultraviolet lamp having its input endface located at the ultraviolet lamp and its output endface at a display panel whereby identification of a particular ultraviolet lamp that has failed may be easily detected. Photocell detector means are provided to detect the light output at the output endface of the light conductor fiber and to produce an alarm signal when said light output fails.