Description:

Bausch + Lomb’s Spectronic 20 is a rugged single-beam spectrophotometer that lets users pick any wavelength in the visible spectrum (340–950 nm) by simply turning its λ-knob. A fixed 20 nm spectral slit width and phototube detector give reliable absorbance or percent-transmittance readings on the analog meter, while a filter lever swaps between two optimized detector/filter sets for the 340-599 nm and 600-950 nm bands. Built to accept standard ½-inch round test tubes (or cuvettes via an adapter) and offering a 1 V DC analog output for chart recorders, the bench-top unit warms up in minutes and needs almost no maintenance—just lamp changes and occasional calibration.

Economic Advantage:

When it debuted in 1953 the “Spec 20” cost a fraction of existing spectrophotometers, instantly opening quantitative colorimetric analysis to teaching labs, clinics, and small industrial QC lines. Its moderate 20 nm bandpass was “good enough” for most routine assays, and the uncomplicated knob-and-meter interface meant technicians could be trained in minutes—dramatically slashing both capital outlay and labor costs compared with UV/Vis instruments of the day. More than 600 000 units sold, and the design became a de-facto standard that students still learn on today.