---
title: "Spectronic 20"
chunk: 2/2
source: "https://en.wikipedia.org/wiki/Spectronic_20"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:42:09.986392+00:00"
instance: "kb-cron"
---

== Use ==
Before testing a sample, the Spectronic 20 is calibrated using a blank solution, which is the pure solvent that is used in the experimental sample.  It is typically water or an organic solvent.  In this calibration, the transmittance is set at 100% using the calibration knob of the instrument (the amplifier control knob in the figure at right). The instrument can also optionally be calibrated with a stock solution of a sample at a concentration known to have an absorbance of 2 or else vendor supplied standards, using the light absorption knob in the diagram shown at right. After calibration, the user places a 1/2 inch test tube or cuvette containing the sample solution to be measured into the sample compartment. Calibration is repeated each time the wavelength is changed. It or a standard reference sample is generally used to periodically check for drift. To measure wavelengths above 650 nm, the bottom of the instrument is opened, and a red filter and a red-sensitive photocell is installed.
The original design of the Spectronic 20 utilized an analog dial for readout of transmission from 100%T to 1%T (top scale), 0A - 2A (lower scale). Using the original instrument requires manual setting of the wavelength and making readings from a moving-needle analog display.

== Replacement ==
The Spectronic 20D (launched in 1985) and later the 20D+ replaced the analog dial with a red digital LED readout, offering greater precision in the readout, if not greater accuracy in the actual reading.  A side-by-side comparison of the features of the 20+ and 20D+ is available in the 2001 operating manual.
The Spectronic 20 was replaced by the Spectronic 200 in the Thermo Scientific spectrophotometer product line in 2011. The Spectronic 200 utilizes an array detector and digital control of the measured wavelength, while retaining the characteristic λ knob of the Spec 20 for setting the wavelength. In addition to replicating the user modes of the Spec 20D+ (which it can emulate on a color LCD screen) the Spec 200 accommodates both test-tubes and square cuvettes without needing to install an adapter. Software modes described in the Spectronic 200's specifications include scanning, four wavelength simultaneous measurement, and quantitative analysis with up to four standards, in contrast to the SPEC 20D+ which offered only single point calibration.

== Product line history ==
Originally introduced by Bausch & Lomb in 1953,  the product line was sold to Milton Roy in 1985. Milton Roy sold its instrument group to Life Sciences International, renamed Spectronic Instruments, Inc. in 1995. Spectronics Instruments was purchased by Thermo Optek in 1997, renamed Spectronic-Unicam in 2001 and Thermo-Spectronic in 2002. In 2003 the product line was moved to Madison, WI and the brand renamed to Thermo Electron.
With the merger of Thermo Electron and Fisher Scientific in 2006 the brand changed to Thermo Scientific, and remained such until the end of the production run. Spectronic 20 instruments found in labs today may bear any of the Bausch and Lomb, Milton Roy, Spectronic, Thermo Electron or Thermo Scientific brand names.

== Popular culture ==
The Spectronic 20 is apparently one of the few lab instruments to remain intact after the destruction of the laboratory in the movie Back to the Future.

== References ==

== External links ==
Spectronic 20, ChemLab Images and instructions (from Dartmouth College)
Manufacturer's SPEC 200 webpage (from current manufacturer)