1)Filter based UV-vis detector –     Typically set at 254 nm using               the most prominent band in                  Hg spectrum – can also use 313,       365, 334 nm and other lines as well
2)Variable wavelength detectors – use continuum source like (D2 or H2) & a monochromator, select any l, less sensitive
3)PDA - D2 or H2 source, disperse & focus on diode array, get complete spectrum every 1 sec, powerful, expensive, less sensitive, lots of data generated