Spectrophotometry is a quantitative measurement technique that determines how much light a sample absorbs or transmits at specific wavelengths. In medical devices, it enables clinical chemistry, immunoassay, and point-of-care analyzers to measure analyte concentrations, following the Beer-Lambert law and referenced standards like IEC 61010-2-101.
What is spectrophotometry?
Spectrophotometry measures the intensity of light before and after it passes through a sample, then compares the two to quantify how much was absorbed. The core principle is the Beer-Lambert law: absorbance is proportional to analyte concentration and optical path length. Instruments range from single-wavelength colorimeters to full UV-Vis (ultraviolet-visible) and infrared spectrophotometers.
In medical devices, spectrophotometry sits at the detection layer of many diagnostic platforms. It converts a chemical or biological event (a color change, an enzymatic reaction, a labeled binding event) into an electrical signal a controller can process. That signal is then mapped to a clinically meaningful result such as glucose, hemoglobin, bilirubin, or cholesterol concentration.
Why spectrophotometry matters in medical device development
The quality of a spectrophotometric measurement directly drives the accuracy of a diagnostic result. A photometer with drift, stray light, or wavelength inaccuracy will read the wrong absorbance, and the analyzer will report the wrong concentration. That has patient-safety consequences: misclassified analytes lead to missed diagnoses or inappropriate treatment decisions.
Regulatory exposure is real. Under EU IVDR 2017/746 and FDA 21 CFR Part 862, an IVD manufacturer must demonstrate analytical performance, including precision, linearity, and limit of detection. Poor optical design shows up in verification failures, post-market complaints, and CAPA workload. An optical bench redesigned after clinical evaluation is one of the most expensive rework events a diagnostics program can face, so getting spectrophotometry right early protects timelines and market access.
How spectrophotometry works
A typical spectrophotometer has five functional blocks:
- Light source (tungsten-halogen, deuterium, LED, or laser diode), selected for the wavelength range required.
- Wavelength selector, either a monochromator (prism or grating) or optical filters, that isolates the target wavelength.
- Sample holder or flow cell (cuvette, microplate well, or microfluidic channel) with a defined optical path length.
- Photodetector (photodiode, photomultiplier tube, or CCD/CMOS array) that converts transmitted light into a current.
- Signal chain and firmware that computes absorbance and applies calibration curves.
The measurement compares light intensity through the sample against a reference (blank), then applies the Beer-Lambert relationship A = ε × c × L, where ε is molar absorptivity, c is concentration, and L is path length.
For MedTech instruments, several standards frame design and verification. IEC 61010-1:2010+A1:2016 sets general electrical and mechanical safety for laboratory measurement equipment, with IEC 61010-2-101:2018 adding particular requirements for IVDs. IEC 61326-2-6 covers EMC. Risk activities follow ISO 14971:2019, and quality management follows ISO 13485:2016 (or FDA QMSR, effective February 2, 2026). Embedded firmware falls under IEC 62304.
Common challenges and best practices
Optical detection looks simple on paper and rarely is in practice. A few failure modes recur across programs.
Wavelength drift and lamp aging skew absorbance over time. Good designs schedule lamp intensity monitoring and offer replaceable, factory-calibrated modules.
Stray light inflates absorbance readings at high concentrations, so shielding, baffles, and filter selection matter more than the datasheet suggests.
Cuvette or flow-cell tolerances change the effective path length, which directly biases results; tightening dimensional control at the manufacturing stage often costs less than a global calibration campaign later.
Temperature is another quiet source of error. Detector dark current, LED output, and enzymatic reaction rates all shift with temperature, so thermal control on the optical bench is worth designing in.
On the software side, ADC resolution, noise floor, and blank-subtraction logic need verification against real reagent lots, not synthetic signals. Teams that build a disciplined reference-standard protocol into design verification, using traceable neutral-density filters and certified reference materials, catch these issues before clinical evaluation begins.
How SJML helps with spectrophotometry
SJML brings optics and photonics engineering together with the disciplines of IVD product development. Our teams have designed and industrialized point-of-care and microfluidics diagnostic platforms where spectrophotometric detection sits at the core of the measurement chain, along with imaging systems that share the same optical engineering base. On the compliance side, our QARA group supports IVD manufacturers with IEC 61010-2-101 evaluation, IEC 61326-2-6 EMC planning, ISO 14971 risk files, and IVDR technical documentation. Manufacturing capability includes ISO Class 7 and 8 cleanrooms, PCBA with AOI and X-ray inspection, and precision optics-adjacent assembly for stable, repeatable instrument builds.
Talk to SJML’s engineering team →
Frequently asked questions
Colorimetry is a subset of spectrophotometry that works only in the visible range and typically at fixed wavelengths using filters. Spectrophotometry covers a broader range (UV, visible, near-infrared) and uses either filters or a monochromator for wavelength selection. Most modern MedTech analyzers are spectrophotometric because they need selectable wavelengths for multi-analyte panels and higher analytical specificity.
For laboratory-based spectrophotometers, IEC 61010-1:2010+A1:2016 governs general safety, and IEC 61010-2-101:2018 covers particular requirements for IVD equipment. EMC follows IEC 61326-2-6. Quality management aligns with ISO 13485:2016, and risk management with ISO 14971:2019. In the EU, IVD instruments fall under IVDR 2017/746; in the US, they follow the QMSR (21 CFR Part 820) and applicable product classifications such as 21 CFR Part 862.
The Beer-Lambert law states that absorbance equals molar absorptivity times concentration times path length. Instrument designers use it to size the optical path, select detector sensitivity, and set the expected absorbance range for target analytes. Deviations from linearity at high concentrations, caused by stray light or detector saturation, are treated as design inputs and drive the working range specified in the instrument’s analytical performance claims.
Not directly. IEC 60601-1 covers medical electrical equipment that has an applied part connected to a patient. A benchtop spectrophotometer used on samples in vitro falls under the IEC 61010 series instead. If a spectrophotometric detection module is built into a device with patient-applied parts, such as some pulse oximeters or transcutaneous monitors, then IEC 60601-1 and the relevant particular standard apply.
Related terms
- Beer-Lambert Law
- In Vitro Diagnostic (IVD) Device
- Design Verification
- Clinical Chemistry Analyzer
- Optical Detection Systems
