Although the first DU prototype used glass, all later models contained quartz prisms which functioned as chromators. They transmitted and separated the light generated by a hydrogen lamp into its absorption spectrum, allowing it to be measured by phototubes. The quartz used by National Technical Laboratories was difficult to obtain during World War II, and Arnold Beckman had to seek a wartime priority listing for the spectrophotometer in order to import optical quality quartz from Brazil.

The first Beckman Instruments DU Spectrophotometer was developed in 1940, when the company was still called National Technical Laboratories. Spurred by employee Howard Cary (who had previously been involved in pH meter development), NTL produced its first DU Spectrophotometer prototype in 1940. The DU was initially developed under a U.S. government contract, but was ultimately used in many important scientific discoveries and developments of the 20th century, including penicillin and synthetic rubber research, petroleum refining, and the creation of explosives.