Both spectrophotometers and densitometers are colour measurement instruments used in the printing industry, and both are associated with the X-Rite name. The confusion between them is understandable — they are both held against printed surfaces and produce numerical measurements — but they measure different things, serve different purposes, and provide different kinds of quality control value. Knowing which you need, and why, is important for building the right colour management workflow for your production environment.
A densitometer measures the optical density of a printed ink layer — effectively, how much light the ink absorbs. It produces a single number (a density value) for each primary ink colour (cyan, magenta, yellow, and black in four-colour printing). Density is directly related to the amount of ink laid down on the substrate: a higher density reading means more ink, a lower reading means less. Press operators have used densitometers for decades to control ink key settings and ensure consistent ink coverage across a print run. Density control is fast, practical, and effective for managing the mechanical variables of the printing process.
A spectrophotometer, as described in the companion article, measures how a surface reflects light across the full visible spectrum, producing a spectral reflectance curve that can be converted into colour values (L\*a\*b\*), colour difference calculations (ΔE), and a range of other derived measurements. A spectrophotometer can measure everything a densitometer can measure (density values can be derived from spectral data), but it captures far more information — enough to precisely characterise the colour of any surface, compare it against any standard, and detect colour differences that would be invisible to a densitometer.
What Densitometers Do Well
Densitometers are fast, simple, and highly practical for process control tasks in offset printing. A press operator who needs to check whether the cyan ink key is delivering the right ink film thickness does not need spectral data — they need a density reading, and a densitometer provides it instantly. Densitometers are also robust: they have fewer optical components than spectrophotometers, making them more durable in demanding press-side environments.
For printing operations working with process colour (CMYK) to simple tolerances, densitometry provides adequate quality control at lower cost than spectrophotometry. Many press operators who have been in the industry for years are highly skilled density readers, able to use density data to diagnose process problems quickly and accurately. This practical expertise is a real asset in high-volume, process-colour printing environments.
However, densitometers have fundamental limitations. They cannot tell you what a colour looks like — only how much ink is present. Two prints with the same density reading may look completely different in colour if the ink's pigment distribution has changed, if the substrate colour has shifted, or if metamerism is a factor. Densitometers also cannot measure spot colours (Pantone and other single-pigment inks) against a specification in colour terms — they can only tell you the density of the ink layer, not whether the colour is right.
Where Spectrophotometers Are Essential
Spectrophotometers are essential when colour accuracy — not just ink density — is the quality requirement. Brand colour matching, Pantone verification, cross-substrate colour consistency, and Delta E tolerance compliance all require spectrophotometric measurement. No densitometer can tell you whether your Pantone 485 red is within ΔE 2.0 of the standard. Only a spectrophotometer can.
In commercial packaging printing — where brand owners specify colour in Pantone or LAB terms, set Delta E tolerances, and require documented measurement compliance records — spectrophotometry is the standard measurement method. The eXact 2 spectrophotometer combines the speed and durability needed for press-side use with full spectrophotometric capability, making it the industry's preferred single instrument for both density control and colour measurement.
The advantage of a combined spectrophotometer/densitometer instrument like the eXact 2 is that it provides everything a press operator needs from one device: density readings for process control, spectral data for colour verification, and Delta E calculations for compliance reporting. This combination has made dedicated stand-alone densitometers less common in modern commercial printing operations, where brand colour specifications have driven the shift toward comprehensive spectrophotometric measurement.
For industries outside printing — plastics, textiles, coatings, automotive — spectrophotometers are the only relevant instrument type. Densitometry has no application in these fields. The handheld Ci series spectrophotometers and benchtop spectrophotometers address these non-printing applications with geometries and aperture sizes suited to the surface types and sample formats encountered in industrial manufacturing.
Conclusion
Densitometers and spectrophotometers both have roles in colour quality management, but they operate at different levels of measurement depth. A densitometer tells you how much ink is on the paper — a useful process control metric in printing. A spectrophotometer tells you what colour the surface actually is — an essential piece of information for any quality management program built around colour accuracy. For most professional colour management applications today, the spectrophotometer's ability to measure colour in absolute terms, compare against standards, and generate documented compliance data makes it the instrument of choice — and the eXact 2 from X-Rite delivers both density and spectrophotometric capability in a single, production-ready instrument.