The Beckman DU was not only a revolutionary instrument for its myriad uses and applications, but its optical design was the standard by which all others were judged for many years. Several key features distinguished the Beckman DU from its competitors. The first was the light source itself, a special molecular hydrogen lamp designed by Arnold Beckman and Howard Cary specifically for the DU. The second was the monochromator, composed of a large, Brazilian quartz prism for superior optical purity. Finally, the DU employed a special UV-sensitive phototube designed by Beckman and Cary for the DU and produced by Beckman Instruments.

Though its design appears deceivingly simple by today's standards, the optics of the Beckman DU spawned many imitators and influenced generations of instruments. What makes this instrument even more amazing is that it was the first of its kind; there were no UV-vis instruments before the DU to learn from and improve.

The optics of the DU are presented in the movie below in simplified form.

The Beckman DU was designed from the ground up, including the hydrogen lamp, monochromator, and UV-sensitive phototube, in only 14 months.

Howard Cary, lead designer for the DU and the Beckman G pH meter, later left Beckman instruments to start his own company, Applied Physics Corporation. The Cary 14, one of his designs, is widely regarded as the finest dispersive optical instrument ever made.