The Waters 490 is famous for it's use of a pulsed xenon lamp. The trademark sound coming from a 490 could be heard as a high pitched, but soft "ting-ting-ting". There are some remarkable engineering characteristics behind this detector, but the unique optical design I was told came from a Waters engineer flying in a plane observing the pulsing pattern of the landing lights on a landing strip. The detector was heavy on moving parts, ahead of it's time technically, but for sure it lost the war ultimately to Diode Array technology. If there was ever a scientific instrument that deserves to be studied for unique characteristics, it is the Waters 490 which saw the bulk of it's service life thru the 1980's.   
  
UV/VIS Detector with a programmable multiwavelength with four independently programmable channels. Real-time peak purity confirmation with Ratioplot, Windowplot and maxplot routines.  Powerline programmability of wavelength, attenuation, autozero, polarity, and time constant. Wide wavelength and sensitivity range from 190 to 600 nm, 0.001 to 3 AUFS.